origin and structure of the earth essay

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Chapter 3: The Origin and Structure of Earth

Learning objectives.

After reading this chapter you should be able to:

• recall the age of the universe, the solar system, and Earth
• explain the processes responsible for the early formation of Earth
• identify the names and composition of the various layers of the Earth
• explain the differences between oceanic and continental crust
• explain the difference between lithosphere and asthenosphere
• define the concept of isostasy
• explain how indirect methods can be used to investigate the interior of Earth

To understand the geological processes occurring in the ocean, it is important to recognize some of the phenomena that led to the formation and structure of the Earth. In this chapter we will start at the very beginning, with a discussion of the Big Bang and the origin of the universe and our solar system . From there, we will investigate the formation of the Earth, and the reasons behind its interior and exterior structure. Finally, we will end the chapter by attempting to answer the question of how we can know what is happening deep within the Earth’s interior.

the theory that the universe started with a giant expansion approximately 13.77 billion years ago (3.1)

a star and the planets surrounding it (3.1)

Introduction to Oceanography Copyright © by Paul Webb is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Earth Structure

The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. Each layer has a unique chemical composition, physical state, and can impact life on Earth's surface. Movement in the mantle caused by variations in heat from the core, cause the plates to shift, which can cause earthquakes and volcanic eruptions. These natural hazards then change our landscape, and in some cases, threaten lives and property. Learn more about how the earth is constructed with these classroom resources.

Earth Science, Geology, Geography, Physical Geography

• Study Guides
• A Summary of Earth's History
• The Earth's Exterior
• Geologic Time
• The Earth Today
• History of Physical Geology
• The Earth's Origin
• The Earth's Structure
• Mineral Properties
• The Rock Cycle
• Chemical Composition
• Minerals and Rocks
• Extrusive Rock Types
• Rock Textures
• Intrusive Rock Types
• Intrusive Structures
• How Different Magmas Form
• Igneous Rocks and Plate Tectonics
• Magmatic Differentiation
• Volcanoes and Lavas
• Clastic Sedimentary Rocks
• Chemical Sedimentary Rocks
• Organic Sedimentary Rocks
• Sedimentary Features
• Sedimentary Environments
• How Sedimentary Rocks Form
• Factors Controlling Metamorphism
• Types of Metamorphism
• Metamorphic Rock Types
• Hydrothermal Rocks
• Metamorphism and Plate Tectonics
• Metamorphism Defined
• Interpreting Structures
• Mapping in the Field
• Unconformities
• Geologic Structures Defined
• Tectonic Forces
• Processes of Mechanical Weathering
• Processes of Chemical Weathering
• Prevention of Mass Wasting
• Introduction to Mass Wasting
• Mass‐Wasting Controls
• Types of Mass Wasting
• Stream Dynamics
• Stream Erosion
• Sediment Load
• Stream Deposition
• Stream Valleys
• Regional Erosion
• Types of Water Flow
• How Glaciers Develop
• Glacier Movement
• Glacial Erosion
• Glacial Landforms
• Glacial Deposits
• Glaciers in the Past
• Introduction to Glaciation
• Types of Glaciers
• North American Glaciation
• Permeability
• The Water Table
• Streams and Springs
• Effects of Groundwater Flow
• Groundwater Pollution
• Geothermal Energy
• Groundwater and Infiltration
• Shoreline Features
• Desert Features
• The Effects of Wind
• Distribution and Causes of Deserts
• Monitoring Earthquakes
• Effects of Earthquakes
• Earthquakes and Plate Tectonics
• Control and Prediction
• How Earthquakes Form
• Seismic Waves
• Isostatic Equilibrium
• Magnetic Fields
• Geophysics Defined
• Seismic Waves: Methods of Detection
• The Structure of the Earth
• Geothermal Gradients
• Continental Margins
• Ocean Floor Sediments
• Active Continental Margins
• Passive Continental Margins
• Investigative Technologies
• Midoceanic Ridges
• Oceanic Crust
• How Plates Move
• Types of Plate Boundaries
• Why Plates Move
• Mantle Plumes
• Early Evidence for Plate Tectonics
• Paleomagnetic Evidence
• Sea Floor Evidence
• Features of Mountain Belts
• Types of Mountains
• How Mountains Form
• How Continents Form
• Introduction to Mountains
• Geologic Correlations
• Absolute Age
• Geologic Time Defined
• Relative Time
• Metallic Deposits
• Energy Resources
• Nonmetallic Resources
• Recycling and Conservation
• Resources and Reserves
• Earth's Moon
• Jupiter and Saturn
• Introduction to the Solar System

The Precambrian. The vast unit of time known as the Precambrian started with the origin of the earth about 4.5 billion years ago and ended 570 million years ago. Largely thought to be a hot, steaming, and forbidding landscape, the primitive crust of the newly condensed planet continued to cool. The crust consisted largely of igneous intrusions and volcanic rocks, and sediments that were eroded from this irregular surface. Geologic remnants from this time are the highly deformed and metamorphosed cratons of the continents. The Precambrian is subdivided, from oldest to youngest, into three eons, the Hadean (4600−3900 million years ago), Archean (3900−2500 million years ago), and Proterozoic (2500−570 million years ago). Little is known about the Hadean because there are so few rocks of that age, and those that do exist are intensely deformed and metamorphosed. The Archean was dominated by crustal building and the development of extensive volcanic belts, arcs, and sedimentary basins that were probably related to plate tectonic activity. Marine rocks including chert contain the fossil remains of microscopic algae and bacteria. The Proterozoic is known for large‐scale rifting of continental crust across the world and the filling of these rifts with huge amounts of sedimentary and volcanic rocks. Extensive iron deposits formed in shallow Proterozoic seas, indicating there was enough free oxygen to precipitate iron oxide minerals (for example, hematite [Fe 2 O 3 ]) from the iron in the water. The increase in the amount of free oxygen is thought to be a result of photosynthetic action by primitive life forms in the sea. The fossil record has preserved layered algal mounds called stromatolites, an abundance of microscopic species, and trails and burrows from wormlike organisms.

The Paleozoic era. The Paleozoic era (570−245 million years ago) was long believed by geologists to mark the beginning of life, because of the sudden abundance of complex organisms with hard parts in the fossil record. These organisms included trilobites and shelled animals called cephalopods (cephalopods were the ancestors of modern squids and octopi). Life was restricted to the sea and included graptolites, brachiopods, bryozoans, and mollusks.

A single southern landmass consisted of what is today South America, Africa, India, Antarctica, and Australia. In the northern hemisphere, land masses that represent North America, Siberia, northern Europe, western Asia, and China had not yet joined the southern landmass. North America was essentially a lowland that was periodically flooded by the ocean, forming extensive deposits of sandstone, limestone, and barrier reefs.

By the end of the Paleozoic, all of the continents had come together to form Pangaea. This formation resulted in extreme seasonal weather conditions and one of the greatest periods of extinction in the earth's history—up to 75 percent of amphibian species and 80 percent of marine species disappeared. This time was also marked by the rapid development of land plants, forests of short trees, armor‐plated fishes, sharks, and bony fishes. The Devonian period, the fourth period in the Paleozoic era, is known as the “Age of the Fishes.” Air‐breathing amphibians began to move from the ocean to land. Large tropical swamps dominated much of the landscape.

The Mesozoic era. The Mesozoic era occurred from about 245 million to 66 million years ago. The fossil record from this era (the “Age of the Dinosaurs”) is dominated by a multitude of dinosaur species. Common sedimentary deposits are red sandstones and mudstones. The low‐lying areas were frequently flooded by shallow marine transgressions. Tropical conditions resulted in extensive swamps that later became coal beds. By the mid‐Mesozoic, Pangaea rifted into northern Laurasia and southern Gondwanaland. Igneous and volcanic activity formed the mountain ranges in western North America.

In the Mesozoic era, new trees such as conifers and ginkgoes appeared. Reptiles laid eggs on land. Dinosaur species included meateaters, herbivores, winged reptiles, and marine reptiles. Mammals were just beginning to emerge during this time. The end of the Mesozoic is marked by more mass extinctions, especially of the dinosaurs. Surviving species included turtles, snakes, crocodiles, and various lizards.

The Cenozoic era. The Cenozoic era , also called the “Age of Recent Life” or “Age of Mammals,” encompasses the last 66 million years of the earth's history. Life forms continued to become more complex. The Cenozoic has the most complete geologic record of any era because it is so recent. The continents were fully separated. Plate tectonic activity created many orogenic and volcanic events in North America, including the western fault‐block mountains and huge lava flows. Eastern North America was tectonically stable, and the Appalachians eroded to lower elevations. Valleys in the western part of the continent were filled with great thicknesses of sediments from the mountain ranges.

The fossil record indicates a diverse array of mammals (including marsupials and placentals), flowering plants, grasses, and microscopic foraminifera. New birds and mammals evolved that were adapted to the new vegetation species. Prehistoric humans also began to emerge. Waves of mass extinctions occurred toward the end of Pleistocene epoch, including those of mammoths, mastodons, sabertoothed cats, ground sloths, and camels. North America underwent multiple glaciations in the last 20,000 years, which helped mold the landscapes we see today.

Previous Absolute Age

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Earth’s Structure and Formation Expository Essay

Question 1: advances in determining the age of the earth and the importance of radioactivity.

There are several technological advances that may be used to determine the age of the earth. First, radioactive decay can act as a valuable process in establishing the age of rocks. Following the discovery of radioactive decay, several other age dating techniques emerged, which enabled scientists to position absolute ages against the geological scale of time.

Radioactivity discovery and the knowledge that the quantities of neutrons in an element may diverge to form isotopes, facilitated in establishing two key tools that are useful in understanding geosphere (Fried, 2000). Radiometric age dating, which is the first tool, becomes founded on the fact that some isotopes have predictable decay rates, on top of being unstable.

Hence, knowledge of the isotope that was present during the formation of the rock and the rate at which the unstable isotope changes can be used to establish the age of the rock depending on the current isotopic composition of the rock. The second tool utilizes stable isotopes, whereby the relative quantity of isotopes in an organic compound or rock may aid in establishing its origin.

There exist other technologies that can be used to study geology, besides, isotopic geology. For instance, laboratory technologies, which include the use of new tools to find out the composition of organic compounds and rocks, can also be used to study geology (Fried, 2000).

There is also, advancement in the ability to determine magnetic features of materials as well as understanding magnetism. In addition, paleomagnetism enables geologists to establish the age of rocks and the latitude of the rock during the cooling process. Paleomagnetism has enabled geologists to trace past positions of continents.

Lastly, advances in laboratory tools of analysis become steered by development in field techniques. The majority of such techniques are remote sensing in nature. Some remote sensing tools include seismology and sonar.

Question 2: What makes the Earth a Habitable Place?

The earth is habitable as it gets positioned at a distance from the sun which allows water to exist in all its forms, including the liquid form. Besides, the earth has an atmosphere and a magnetic field that obstructs detrimental radiation from the sun. Also, the earth has vigorous tectonic processes, which stimulate an exchange between external and internal layers of the planet, in order to reuse biological and geological substances.

However, the earth was not habitable from the start. In the early stages of formation, the earth was not habitable, due to the bombardment by planetesimals, during the Big bang theory. A few seconds after the Big bang neutrons and protons began to form nuclei of elements such as Helium and Hydrogen. In the first hundred thousand years after the bang, no matter of the state, that is common, existed.

Rather, the earth became dominated by radiation. Following radiation, nuclei joined with free electrons, to form atoms and matter grew dominant over energy, gradually. 200 Million years later, galaxies began to form out of condensed gas, and the solar system emerged.

Question 3: Alfred Wegener, Skepticism and Proof of the Continental Drift Hypotheses

Wegener suggested the theory of the continental drift. However, Wegener’s work became viewed with skepticism. Some scientists argued that Wegener’s idea of continents drifting on the earth’s surface was illogical. This was because Wegener did not explain where the energy to drive the movement would originate. Also, a physicist demonstrated that continental drifting over the surface of the earth, would make all continents drift to the equator (Monroe, 2012).

This was a key source of disprove for Wegener’s theory, since not all continents are around the equator, billion of years later. However, the acquisition of new data supported Wegener’s hypothesis. The discovery of regular reversals from magnetization of bordering strips of the ocean floor supported the idea of seafloor spreading (Monroe, 2012).

Wegener supported his theory by use of disciplines including biology, geography and geology. He inquired how coal deposits became sited near the North Pole and how African plains demonstrated glaciations. Besides, Wegener demonstrated areas that fossils of identical prehistoric species became dispersed.

Question 4: Seismic Tomography

Seismic tomography employs seismic waves in order to visualize all the three sides of the mantle (Iyer, 1993). Scientists then form images of individual slices in the interior of the earth, which can be used to explain geology and the composition of the earth’s interior.

Seismic tomography shows magnetic variances from the floor of the ocean, which confirms the occurrence of the sea floor spreading. Also, scientists can see aspects like the Indian ridge systems and the East-pacific rise, as well as volcanoes near the Pacific Rim, which confirm the presence of plate tectonics (Iyer, 1993).

Question 5: The Laws of Thermodynamics

The laws of thermodynamics determine the motions that result in the formation of mountains and oceans. The first law of thermodynamics states that energy can not be destroyed, although, it may be converted from one state to another. The second law proposes that energy tends to disband from areas of high concentration to areas of low concentration. In order to explain the motions that result in the formation of mountains and oceans, we shall focus on the second law.

During the formation of the solar system, a thin stream of Helium and Hydrogen dispersed to space. Thus, heavier elements became formed from lighter ones, including stars and planetary systems. In the process, the planet developed surface features such as oceans and mountains.

Fried, B. (2000). Rocks and minerals . Portland, Me: Weston Walch.

Iyer, H.M. (1993). Seismic tomography: Theory and practice . New York: Chapman & Hall.

Monroe, J. (2012). The changing earth: Exploring geology and evolution . Belmont, CA: Brooks/Cole.

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3.1: Origin of Earth and the Solar System

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According to the Big Bang theory , the universe blinked violently into existence 13.77 billion years ago (Figure \(\PageIndex{1}\)). The Big Bang is often described as an explosion, but imagining it as an enormous fireball isn’t accurate. The Big Bang involved a sudden expansion of matter, energy, and space from a single point. The kind of Hollywood explosion that might come to mind involves expansion of matter and energy within space, but during the big bang, space itself was created.

At the start of the Big Bang, the universe was too hot and dense to be anything but a sizzle of particles smaller than atoms, but as it expanded, it also cooled. Eventually some of the particles collided and stuck together. Those collisions produced hydrogen and helium, the most common elements in the universe, along with a small amount of lithium. Gravity caused clouds of these early elements to coalesce into stars, and it was inside these stars that heavier elements were formed

Our solar system began to form around 5 billion years ago, roughly 8.7 billion years after the Big Bang. A solar system consists of a collection of objects orbiting one or more central stars. All solar systems start out the same way. They begin in a cloud of gas and dust called a nebula . Nebulae are some of the most beautiful objects that have been photographed in space, with vibrant colors from the gases and dust they contain, and brilliant twinkling from the many stars that have formed within them (Figure \(\PageIndex{2}\)). The gas consists largely of hydrogen and helium, and the dust consists of tiny mineral grains, ice crystals, and organic particles.

A solar system begins to form when a small patch within a nebula (small by the standards of the universe, that is) begins to collapse upon itself. Exactly how this starts isn’t clear, although it might be triggered by the violent behavior of nearby stars as they progress through their life cycles. Energy and matter released by these stars might compress the gas and dust in nearby neighborhoods within the nebula. Once it is triggered, the collapse of gas and dust within that patch continues for two reasons. One of those reasons is that gravitational force pulls gas molecules and dust particles together. But early in the process, those particles are very small, so the gravitational force between them isn’t strong. So how do they come together? The answer is that dust first accumulates in loose clumps for the same reason dust bunnies form under your bed: static electricity. As the small patch within a nebula condenses, a star begins to form from material drawn into the center of the patch, and the remaining dust and gas settle into a disk that rotates around the star. The disk is where planets eventually form, so it’s called a protoplanetary disk . In Figure \(\PageIndex{3}\) the image in the upper left shows an artist’s impression of a protoplanetary disk, and the image in the upper right shows an actual protoplanetary disk surrounding the star HL Tauri. Notice the dark rings in the protoplanetary disk. These are gaps where planets are beginning to form. The rings are there because incipient planets are beginning to collect the dust and gas in their orbits. There is an analogy for this in our own solar system, because the dark rings are akin to the gaps in the rings of Saturn (Figure \(\PageIndex{3}\), lower left), where moons can be found (Figure \(\PageIndex{3}\), lower right).

In general, planets can be classified into three categories based on what they are made of (Figure \(\PageIndex{4}\)). Terrestrial planets are those planets like Earth, Mercury, Venus, and Mars that have a core of metal surrounded by rock. Jovian planets (also called gas giants ) are those planets like Jupiter and Saturn that consist predominantly of hydrogen and helium. Ice giants are planets such as Uranus and Neptune that consist largely of water ice, methane (CH 4 ) ice, and ammonia (NH 3 ) ice, and have rocky cores. Often, the ice giant planets Uranus and Neptune are grouped with Jupiter and Saturn as gas giants; however, Uranus and Neptune are very different from Jupiter and Saturn.

These three types of planets are not mixed together randomly within our solar system. Instead they occur in a systematic way, with terrestrial planets closest to the sun, followed by the Jovian planets and then the ice giants. Part of the reason for this arrangement is the frost line (also referred to as the snow line ). The frost line separated the inner part of the protoplanetary disk closer to the sun, where it was too hot to permit anything but silicate minerals and metal to crystallize, from the outer part of the disk farther from the Sun, where it was cool enough to allow ice to form. As a result, the objects that formed in the inner part of the protoplanetary disk consist largely of rock and metal, while the objects that formed in the outer part consist largely of gas and ice. The young sun also blasted the solar system with raging solar winds (winds made up of energetic particles), which helped to drive lighter molecules toward the outer part of the protoplanetary disk.

The objects in our solar system formed by accretion . Early in this process, mineral and rock particles collected in fluffy clumps because of static electricity. As the mass of the clumps increased, gravity became more important, pulling material from farther away and growing these solid masses into larger and larger bodies. Eventually the mass of the objects became large enough that their gravity was strong enough to hang onto gas molecules, because gas molecules are very light.

Our Earth formed though this process of accretion about 4.6 billion years ago. The early Earth was very hot and had a molten, fluid composition, with lost of geological and volcanic activity on the surface. The Earth’s heat came from a variety of processes:

• Heat came from the decay of radioactive elements within the Earth, specifically the decay of 235U, 238U, 40K, and 232Th, which are primarily present in the mantle. The total heat produced that way has been decreasing over time (because these isotopes are getting used up), and is now roughly 25% of what it was when Earth formed. This means that Earth’s interior is slowly becoming cooler.
• Heat came from the thermal energy already contained within the objects that accreted to form the Earth.
• Heat came from collisions. When objects hit Earth, some of the energy from their motion went into deforming Earth, and some of it was transformed into heat. (The very worst collision that Earth experienced was with a planet named Theia, which was approximately the size of Mars. Not long after Earth formed, Theia struck Earth. When Theia slammed into Earth, Theia’s metal core merged with Earth’s core, and debris from the outer silicate layers was cast into space, forming a ring of rubble around Earth. The material within the ring coalesced into a new body in orbit around Earth, giving us our moon. Remarkably, the debris may have coalesced in 10 years or fewer! This scenario for the formation of the moon is called the giant impact hypothesis .)
• As Earth became larger, its gravitational force became stronger. This increased Earth’s ability to draw objects to it, but it also caused the material making Earth to be compressed, rather like Earth giving itself a giant gravitational hug. Compression causes materials to heat up.

Heating had a very important consequence for Earth’s structure. As Earth grew, it collected a mixture of silicate mineral grains as well as iron and nickel. These materials were scattered throughout Earth. That changed when Earth began to heat up: it got so hot that both the silicate minerals and the metals melted. The metal melt was much denser than the silicate mineral melt, so the metal melt sank to Earth’s center to become its core, and the silicate melt rose upward to become Earth’s crust and mantle. In other words, Earth unmixed itself. The separation of silicate minerals and metals into a rocky outer layer and a metallic core, respectively, is called differentiation . Gravity has since pulled Earth into an almost spherical shape with a radius of 6371 km, and a circumference of about 40,000 km. However, it is not a perfect sphere, as the Earth’s rotation causes an equatorial bulge, so that the Earth’s circumference is 21 km (0.3%) wider at the equator than it is pole to pole. Thus it is technically an “oblate spheroid.”

If we were to take an inventory of the elements that make up Earth, we would find that 95% of Earth’s mass comes from only four elements: oxygen, magnesium, silicon, and iron. Most of the remaining 5% comes from aluminum, calcium, nickel, hydrogen, and sulphur. We know that the Big Bang made hydrogen, helium, and lithium, but where did the rest of the elements come from? The answer is that the other elements were made by stars. The heat and pressure within stars cause smaller atoms to smash together and fuse into new, larger atoms. For example, when hydrogen atoms smash together and fuse, helium is formed. Large amounts of energy are released when some atoms fuse and that energy is what causes stars to shine.

It takes larger stars to make elements as heavy as iron and nickel. Our Sun is an average star; after it uses up its hydrogen fuel to make helium, and then some of that helium is fused to make small amounts of beryllium, carbon, nitrogen, oxygen, and fluorine, it will be at the end of its life. It will stop making atoms and will cool down and bloat until its middle reaches the orbit of Mars. In contrast, large stars end their lives in spectacular fashion, exploding as supernovae and casting off newly formed atoms —including the elements heavier than iron — into space. It took many generations of stars creating heavier elements and casting them into space before heavier elements were abundant enough to form planets like Earth.

*”Physical Geology” by Steven Earle used under a CC-BY 4.0 international license. Download this book for free at http://open.bccampus.ca

Science and Creationism: A View from the National Academy of Sciences, Second Edition (1999)

Chapter: the origin of the universe, earth, and life, the origin of the universe, earth, and life.

The term "evolution" usually refers to the biological evolution of living things. But the processes by which planets, stars, galaxies, and the universe form and change over time are also types of "evolution." In all of these cases there is change over time, although the processes involved are quite different.

In the late 1920s the American astronomer Edwin Hubble made a very interesting and important discovery. Hubble made observations that he interpreted as showing that distant stars and galaxies are receding from Earth in every direction. Moreover, the velocities of recession increase in proportion with distance, a discovery that has been confirmed by numerous and repeated measurements since Hubble's time. The implication of these findings is that the universe is expanding.

Hubble's hypothesis of an expanding universe leads to certain deductions. One is that the universe was more condensed at a previous time. From this deduction came the suggestion that all the currently observed matter and energy in the universe were initially condensed in a very small and infinitely hot mass. A huge explosion, known as the Big Bang, then sent matter and energy expanding in all directions.

This Big Bang hypothesis led to more testable deductions. One such deduction was that the temperature in deep space today should be several degrees above absolute zero. Observations showed this deduction to be correct. In fact, the Cosmic Microwave Background Explorer (COBE) satellite launched in 1991 confirmed that the background radiation field has exactly the spectrum predicted by a Big Bang origin for the universe.

As the universe expanded, according to current scientific understanding, matter collected into clouds that began to condense and rotate, forming the forerunners of galaxies. Within galaxies, including our own Milky Way galaxy, changes in pressure caused gas and dust to form distinct clouds. In some of these clouds, where there was sufficient mass and the right forces, gravitational attraction caused the cloud to collapse. If the mass of material in the cloud was sufficiently compressed, nuclear reactions began and a star was born.

Some proportion of stars, including our sun, formed in the middle of a flattened spinning disk of material. In the case of our sun, the gas and dust within this disk collided and aggregated into small grains, and the grains formed into larger bodies called planetesimals ("very small planets"), some of which reached diameters of several hundred kilometers. In successive stages these planetesimals coalesced into the nine planets and their numerous satellites. The rocky planets, including Earth, were near the sun, and the gaseous planets were in more distant orbits.

The ages of the universe, our galaxy, the solar system, and Earth can be estimated using modem scientific methods. The age of the universe can be derived from the observed relationship between the velocities of and the distances separating the galaxies. The velocities of distant galaxies can be measured very accurately, but the measurement of distances is more uncertain. Over the past few decades, measurements of the Hubble expansion have led to estimated ages for the universe of between 7 billion and 20 billion years, with the most recent and best measurements within the range of 10 billion to 15 billion years.

A disk of dust and gas, appearing as a dark band in this Hubble Space Telescope photograph, bisects a glowing nebula around a very young star in the constellation Taurus. Similar disks can be seen around other nearby stars and are thought to provide the raw material for planets.

The age of the Milky Way galaxy has been calculated in two ways. One involves studying the observed stages of evolution of different-sized stars in globular clusters. Globular clusters occur in a faint halo surrounding the center of the Galaxy, with each cluster containing from a hundred thousand to a million stars. The very low amounts of elements heavier than hydrogen and helium in these stars indicate that they must have formed early in the history of the Galaxy, before large amounts of heavy elements were created inside the initial generations of stars and later distributed into the interstellar medium through supernova explosions (the Big Bang itself created primarily hydrogen and helium atoms). Estimates of the ages of the stars in globular clusters fall within the range of 11 billion to 16 billion years.

A second method for estimating the age of our galaxy is based on the present abundances of several long-lived radioactive elements in the solar system. Their abundances are set by their rates of production and distribution through exploding

supernovas. According to these calculations, the age of our galaxy is between 9 billion and 16 billion years. Thus, both ways of estimating the age of the Milky Way galaxy agree with each other, and they also are consistent with the independently derived estimate for the age of the universe.

Radioactive elements occurring naturally in rocks and minerals also provide a means of estimating the age of the solar system and Earth. Several of these elements decay with half lives between 700 million and more than 100 billion years (the half life of an element is the time it takes for half of the element to decay radioactively into another element). Using these time-keepers, it is calculated that meteorites, which are fragments of asteroids, formed between 4.53 billion and 4.58 billion years ago (asteroids are small "planetoids" that revolve around the sun and are remnants of the solar nebula that gave rise to the sun and planets). The same radioactive time-keepers applied to the three oldest lunar samples returned to Earth by the Apollo astronauts yield ages between 4.4 billion and 4.5 billion years, providing minimum estimates for the time since the formation of the moon.

The oldest known rocks on Earth occur in northwestern Canada (3.96 billion years), but well-studied rocks nearly as old are also found in other parts of the world. In Western Australia, zircon crystals encased within younger rocks have ages as old as 4.3 billion years, making these tiny crystals the oldest materials so far found on Earth.

The best estimates of Earth's age are obtained by calculating the time required for development of the observed lead isotopes in Earth's oldest lead ores. These estimates yield 4.54 billion years as the age of Earth and of meteorites, and hence of the solar system.

The origins of life cannot be dated as precisely, but there is evidence that bacteria-like organisms lived on Earth 3.5 billion years ago, and they may have existed even earlier, when the first solid crust formed, almost 4 billion years ago. These early organisms must have been simpler than the organisms living today. Furthermore, before the earliest organisms there must have been structures that one would not call "alive" but that are now components of living things. Today, all living organisms store and transmit hereditary information using two kinds of molecules: DNA and RNA. Each of these molecules is in turn composed of four kinds of subunits known as nucleotides. The sequences of nucleotides in particular lengths of DNA or RNA, known as genes, direct the construction of molecules known as proteins, which in turn catalyze biochemical reactions, provide structural components for organisms, and perform many of the other functions on which life depends. Proteins consist of chains of subunits known as amino acids. The sequence of nucleotides in DNA and RNA therefore determines the sequence of amino acids in proteins; this is a central mechanism in all of biology.

Experiments conducted under conditions intended to resemble those present on primitive Earth have resulted in the production of some of the chemical components of proteins, DNA, and RNA. Some of these molecules also have been detected in meteorites from outer space and in interstellar space by astronomers using radio-telescopes. Scientists have concluded that the "building blocks of life" could have been available early in Earth's history.

An important new research avenue has opened with the discovery that certain molecules made of RNA, called ribozymes, can act as catalysts in modem cells. It previously had been thought that only proteins could serve as the catalysts required to carry out specific biochemical functions. Thus, in the early prebiotic world, RNA molecules could have been "autocatalytic"—that is, they could have replicated themselves well before there were any protein catalysts (called enzymes).

Laboratory experiments demonstrate that replicating autocatalytic RNA molecules undergo spontaneous changes and that the variants of RNA molecules with the greatest autocatalytic activity come to prevail in their environments. Some scientists favor the hypothesis that there was an early "RNA world," and they are testing models that lead from RNA to the synthesis of simple DNA and protein molecules. These assemblages of molecules eventually could have become packaged within membranes, thus making up "protocells"—early versions of very simple cells.

For those who are studying the origin of life, the question is no longer whether life could have originated by chemical processes involving nonbiological components. The question instead has become which of many pathways might have been followed to produce the first cells.

Will we ever be able to identify the path of chemical evolution that succeeded in initiating life on Earth? Scientists are designing experiments and speculating about how early Earth could have provided a hospitable site for the segregation of

molecules in units that might have been the first living systems. The recent speculation includes the possibility that the first living cells might have arisen on Mars, seeding Earth via the many meteorites that are known to travel from Mars to our planet.

Of course, even if a living cell were to be made in the laboratory, it would not prove that nature followed the same pathway billions of years ago. But it is the job of science to provide plausible natural explanations for natural phenomena. The study of the origin of life is a very active research area in which important progress is being made, although the consensus among scientists is that none of the current hypotheses has thus far been confirmed. The history of science shows that seemingly intractable problems like this one may become amenable to solution later, as a result of advances in theory, instrumentation, or the discovery of new facts.

Creationist Views of the Origin of the Universe, Earth, and Life

Many religious persons, including many scientists, hold that God created the universe and the various processes driving physical and biological evolution and that these processes then resulted in the creation of galaxies, our solar system, and life on Earth. This belief, which sometimes is termed "theistic evolution," is not in disagreement with scientific explanations of evolution. Indeed, it reflects the remarkable and inspiring character of the physical universe revealed by cosmology, paleontology, molecular biology, and many other scientific disciplines.

The advocates of "creation science" hold a variety of viewpoints. Some claim that Earth and the universe are relatively young, perhaps only 6,000 to 10,000 years old. These individuals often believe that the present physical form of Earth can be explained by "catastrophism," including a worldwide flood, and that all living things (including humans) were created miraculously, essentially in the forms we now find them.

Other advocates of creation science are willing to accept that Earth, the planets, and the stars may have existed for millions of years. But they argue that the various types of organisms, and especially humans, could only have come about with supernatural intervention, because they show "intelligent design."

In this booklet, both these "Young Earth" and "Old Earth" views are referred to as "creationism" or "special creation."

There are no valid scientific data or calculations to substantiate the belief that Earth was created just a few thousand years ago. This document has summarized the vast amount of evidence for the great age of the universe, our galaxy, the solar system, and Earth from astronomy, astrophysics, nuclear physics, geology, geochemistry, and geophysics. Independent scientific methods consistently give an age for Earth and the solar system of about 5 billion years, and an age for our galaxy and the universe that is two to three times greater. These conclusions make the origin of the universe as a whole intelligible, lend coherence to many different branches of science, and form the core conclusions of a remarkable body of knowledge about the origins and behavior of the physical world.

Nor is there any evidence that the entire geological record, with its orderly succession of fossils, is the product of a single universal flood that occurred a few thousand years ago, lasted a little longer than a year, and covered the highest mountains to a depth of several meters. On the contrary, intertidal and terrestrial deposits demonstrate that at no recorded time in the past has the entire planet been under water. Moreover, a universal flood of sufficient magnitude to form the sedimentary rocks seen today, which together are many kilometers thick, would require a volume of water far greater than has ever existed on and in Earth, at least since the formation of the first known solid crust about 4 billion years ago. The belief that Earth's sediments, with their fossils, were deposited in an orderly sequence in a year's time defies all geological observations and physical principles concerning sedimentation rates and possible quantities of suspended solid matter.

Geologists have constructed a detailed history of sediment deposition that links particular bodies of rock in the crust of Earth to particular environments and processes. If petroleum geologists could find more oil and gas by interpreting the record of sedimentary rocks as having resulted from a single flood, they would certainly favor the idea of such a flood, but they do not. Instead, these practical workers agree with academic geologists about the nature of depositional environments and geological time. Petroleum geologists have been pioneers in the recognition of fossil deposits that were formed over millions of years in such environments as meandering rivers, deltas, sandy barrier beaches, and coral reefs.

The example of petroleum geology demonstrates one of the great strengths of science. By using knowledge of the natural world to predict the consequences of our actions, science makes it possible to solve problems and create opportunities using technology. The detailed knowledge required to sustain our civilization could only have been derived through scientific investigation.

The arguments of creationists are not driven by evidence that can be observed in the natural world. Special creation or supernatural intervention is not subjectable to meaningful tests, which require predicting plausible results and then checking these results through observation and experimentation. Indeed, claims of "special creation" reverse the scientific process. The explanation is seen as unalterable, and evidence is sought only to support a particular conclusion by whatever means possible.

While the mechanisms of evolution are still under investigation, scientists universally accept that the cosmos, our planet, and life evolved and continue to evolve. Yet the teaching of evolution to schoolchildren is still contentious.

In Science and Creationism , The National Academy of Sciences states unequivocally that creationism has no place in any science curriculum at any level.

Briefly and clearly, this booklet explores the nature of science, reviews the evidence for the origin of the universe and earth, and explains the current scientific understanding of biological evolution. This edition includes new insights from astronomy and molecular biology.

Attractive in presentation and authoritative in content, Science and Creationism will be useful to anyone concerned about America's scientific literacy: education policymakers, school boards and administrators, curriculum designers, librarians, teachers, parents, and students.

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17 Origin of the Universe and Our Solar System

Learning Objectives

By the end of this chapter, students should be able to:

• Explain the formation of the universe and how we observe it.
• Understand the origin of our solar system .
• Describe how the objects in our solar system are identified, explored, and characterized.
• Describe the types of small bodies in our solar system, their locations, and how they formed.
• Describe the characteristics of the giant planets , terrestrial planets , and small bodies in the solar system.
• Explain what influences the temperature of a planet’s surface.
• Explain why there is geological activity on some planets and not on others.
• Describe different methods for dating planets and the age of the solar system.
• Describe how the characteristics of extrasolar systems help us to model our own solar system.

The universe began 13.77 billion years ago when energy, matter, and space expanded from a single point. Evidence for the big bang is the cosmic “afterglow” from when the universe was still very dense, and red-shifted light from distant galaxies, which tell us the universe is still expanding.

The big bang produced hydrogen, helium, and lithium, but heavier elements come from nuclear fusion reactions in stars. Large stars make elements such as silicon, iron, and magnesium, which are important in forming terrestrial planets. Large stars explode as supernovae and scatter the elements into space.

Planetary systems begin with the collapse of a cloud of gas and dust. Material drawn to the center forms a star, and the remainder forms a disk around the star. Material within the disk clumps together to form planets. In our solar system , rocky planets are closer to the Sun, and ice and gas giants are farther away. This is because temperatures near the Sun were too high for ice to form, but silicate minerals and metals could solidify.

Early Earth was heated by radioactive decay, collisions with bodies from space, and gravitational compression. Heating melted Earth, causing molten metal to sink to Earth’s center and form a core, and silicate melt to float to the surface and form the mantle and crust. A collision with a planet the size of Mars knocked debris into orbit around Earth, and the debris coalesced into the moon. Earth’s atmosphere is the result of volcanic degassing, contributions by comets and meteorites, and photosynthesis.

The search for exoplanets has identified 12 planets that are similar in size to Earth and within the habitable zone of their stars. These are thought to be rocky worlds like Earth, but the compositions of these planets are not known for certain.

17.1 The Big Bang

According to the big bang theory , the universe blinked violently into existence 13.77 billion years ago. The big bang is often described as an explosion, but imagining it as an enormous fireball isn’t accurate. The big bang involved a sudden expansion of matter, energy, and space from a single point. The kind of Hollywood explosion that might come to mind involves expansion of matter and energy within space, but during the big bang, space itself was created.

At the start of the big bang, the universe was too hot and dense to be anything but a sizzle of particles smaller than atoms, but as it expanded, it also cooled. Eventually some of the particles collided and stuck together. Those collisions produced hydrogen and helium, the most common elements in the universe, along with a small amount of lithium.

You may wonder how a universe can be created out of nothing, or how we can know that the big bang happened at all. Creating a universe out of nothing is mostly beyond the scope of this chapter, but there is a way to think about it. The particles that make up the universe have opposites that cancel each other out, similar to the way that we can add the numbers 1 and −1 to get zero (also known as “nothing”). As far as the math goes, having zero is exactly the same as having a 1 and a −1. It is also exactly the same as having a 2 and a −2, a 3 and a −3, two −1s and a 2, and so on. In other words,  nothing is really the potential for something if you divide it into its opposite parts. As for how we can know that the big bang happened at all, there are very good reasons to accept that it is indeed how our universe came to be.

17.1.1 Looking Back to the Early Stages of the Big Bang

The notion of seeing the past is often used metaphorically when we talk about ancient events, but in this case it is meant literally. In our everyday experience, when we watch an event take place, we perceive that we are watching it as it unfolds in real time. In fact, this isn’t true. To see the event, light from that event must travel to our eyes. Light travels very rapidly, but it does not travel instantly. If we were watching a digital clock 1 m away from us change from 11:59 a.m. to 12:00 p.m., we would actually see it turn to 12:00 p.m. three billionths of a second after it happened. This isn’t enough of a delay to cause us to be late for an appointment, but the universe is a very big place, and the “digital clock” in question is often much, much farther away. In fact, the universe is so big that it is convenient to describe distances in terms of light years , or the distance light travels in one year. What this means is that light from distant objects takes so long to get to us that we see those objects as they were at some considerable time in the past. For example, the star Proxima Centauri is 4.24 light years from the sun. If you viewed Proxima Centauri from Earth on January 1, 2015, you would actually see it as it appeared in early October 2010.

We now have tools that are powerful enough to look deep into space and see the arrival of light from early in the universe’s history. Astronomers can detect light from approximately 375,000 years after the big bang is thought to have occurred. Physicists tell us that if the big bang happened, then particles within the universe would still be very close together at this time. They would be so close that light wouldn’t be able to travel far without bumping into another particle and getting scattered in another direction. The effect would be to fill the sky with glowing fog, the “afterglow” from the formation of the universe.

In fact, this is exactly what we see when we look at light from 375,000 years after the big bang. The fog is referred to as the cosmic microwave background (or CMB), and it has been carefully mapped throughout the sky. The map displays the cosmic microwave background as temperature variations, but these variations translate to differences in the density of matter in the early universe. The red patches are the highest density regions and the blue patches are the lowest density. Higher density regions represent the eventual beginnings of stars and planets. The map has been likened to a baby picture of the universe.

17.1.2 The Big Bang is Still Happening, and We Can See the Universe Expanding

The expansion that started with the big bang never stopped. It continues today, and we can see it happening by observing galaxies that large clusters of billions of stars, called galaxies, are moving away from us. (The exception is the Andromeda galaxy with which we are on a collision course.) The astronomer Edwin Hubble came to this conclusion when he observed that the light from other galaxies was red-shifted. The red shift is a consequence of the Doppler effect. This refers to how we see waves when the object that is creating the waves is moving toward us or away from us.

Before we get to the Doppler effect as it pertains to the red shift, let’s see how it works on something more tangible. The swimming duckling is generating waves as it moves through the water. It is generating waves that move forward as well as back, but notice that the ripples ahead of the duckling are closer to each other than the ripples behind the duckling. The distance from one ripple to the next is called the wavelength . The wavelength is shorter in the direction that the duckling is moving, and longer as the duckling moves away.

When waves are in air as sound waves rather than in water as ripples, the different wavelengths manifest as sounds with different pitches—the short wavelengths have a higher pitch, and the long wavelengths have a lower pitch. This is why the pitch of a car’s engine changes as the car races past you.

If you are using an offline version of this text, access the quiz for section 17.1 via the QR code.

17.2 Overview of Our Planetary System [1]

The solar system consists of the Sun and many smaller objects: the planets, their moons and rings, and such “debris” as asteroids , comets , and dust. Decades of observation and spacecraft exploration have revealed that most of these objects formed together with the Sun about 4.5 billion years ago. They represent clumps of material that condensed from an enormous cloud of gas and dust. The central part of this cloud became the Sun, and a small fraction of the material in the outer parts eventually formed the other objects.

During the past 50 years, we have learned more about the solar system than anyone imagined before the space age. In addition to gathering information with powerful new telescopes, we have sent spacecraft directly to many members of the planetary system . (Planetary astronomy is the only branch of our science in which we can, at least vicariously, travel to the objects we want to study.) With evocative names such as  Voyager ,  Pioneer ,  Curiosity , and  Pathfinder , our robot explorers have flown past, orbited, or landed on every planet, returning images and data that have dazzled both astronomers and the public. In the process, we have also investigated two dwarf planets , hundreds of fascinating moons, four ring systems, a dozen asteroids, and several comets (smaller members of our solar system that we will discuss later).

Our probes have penetrated the atmosphere of Jupiter and landed on the surfaces of Venus, Mars, our  Moon , Saturn’s moon Titan, the asteroids Eros, Itokawa, Ryugu, and Bennu, and the Comet Churyumov-Gerasimenko (usually referred to as 67P). Humans have set foot on the Moon and returned samples of its surface soil for laboratory analysis. We have flown a helicopter drone on Mars. We have even discovered other places in our solar system that might be able to support some kind of life.

17.2.1 An Inventory

The Sun, a star that is brighter than about 80% of the stars in the Galaxy, is by far the most massive member of the solar system. It is an enormous ball about 1.4 million kilometers in diameter, with surface layers of incandescent gas and an interior temperature of millions of degrees. The Sun will be discussed in later chapters as our first, and best-studied, example of a star.

Table 17.1: Mass of members of the solar system. Note that the Sun is by far the most massive member of the solar system.

Most of the material of the planets in the solar system is actually concentrated in the largest one, Jupiter , which is more massive than all the rest of the planets combined. Astronomers were able to determine the masses of the planets centuries ago using Kepler’s laws of planetary motion and Newton’s law of gravity to measure the planets’ gravitational effects on one another or on moons that orbit them. Today, we make even more precise measurements of their masses by tracking their gravitational effects on the motion of spacecraft that pass near them.

Beside Earth, five other planets were known to the ancients—Mercury, Venus, Mars, Jupiter, and Saturn—and two were discovered after the invention of the telescope: Uranus and Neptune. The eight planets all revolve in the same direction around the Sun. They orbit in approximately the same plane, like cars traveling on concentric tracks on a giant, flat racecourse. Each planet stays in its own “traffic lane,” following a nearly circular orbit about the Sun and obeying the “traffic” laws discovered by Galileo, Kepler, and Newton. Besides these planets, we have also been discovering smaller worlds beyond Neptune that are called trans-Neptunian object s or TNOs. The first to be found, in 1930, was  Pluto , but others have been discovered during the twenty-first century. One of them,  Eris , is about the same size as Pluto and has at least one moon (Pluto has five known moons). The largest TNOs are also classed as dwarf planets ,  as is the largest asteroid,  Ceres . To date, more than 2600 of these TNOs have been discovered, and one, called Arrokoth, was explored by the New Horizons spacecraft.

Each of the planets and dwarf planets also rotates (spins) about an axis running through it, and in most cases the direction of rotation is the same as the direction of revolution about the Sun. The exceptions are  Venus , which rotates backward very slowly (that is, in a retrograde direction), and Uranus and  Pluto , which also have strange rotations, each spinning about an axis tipped nearly on its side. We do not yet know the spin orientations of Eris, Haumea, and Makemake.

The four planets closest to the Sun (Mercury through Mars) are called the inner or  terrestrial planets . Often, the  Moon is also discussed as a part of this group, bringing the total of terrestrial objects to five (we generally call Earth’s satellite “the Moon,” with a capital M, and the other satellites “moons,” with lowercase m’s). The terrestrial planets are relatively small worlds, composed primarily of rock and metal. All of them have solid surfaces that bear the records of their geological history in the forms of craters , mountains , and volcanoes .

The next four planets (Jupiter through Neptune) are much larger and are composed primarily of lighter ices, liquids, and gases. We call these four the Jovian planets (after “Jove,” another name for Jupiter in mythology) or giant planets —a name they richly deserve. About 1,300 Earths could fit inside Jupiter, for example. These planets do not have solid surfaces on which future explorers might land. They are more like vast, spherical oceans with much smaller, dense cores.

Near the outer edge of the system lies  Pluto , which was the first of the distant icy worlds to be discovered beyond Neptune (Pluto was visited by a spacecraft, the NASA New Horizons mission, in 2015).

Table 17.2: The planets.

The outermost part of the solar system is known as the Kuiper belt , which is a scattering of rocky and icy bodies. Beyond that is the Oort cloud , a zone filled with small and dispersed ice traces. These two locations are where most comets form and continue to orbit, and objects found here have relatively irregular orbits compared to the rest of the solar system. Pluto, formerly the ninth planet, is located in this region of space. The XXVIth General Assembly of the International Astronomical Union (IAU) stripped Pluto of planetary status in 2006 because scientists discovered an object more massive than Pluto, which they named Eris. The IAU decided against including Eris as a planet, and therefore, excluded Pluto as well.

The IAU narrowed the definition of a planet to three criteria: 1) it must orbit a star (in our cosmic neighborhood, the Sun), 2) it must be big enough to have enough gravity to force it into a spherical shape, and 3) it must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun. Pluto passed the first two parts of the definition, but not the third. Pluto and Eris are currently classified as dwarf planets.

17.2.2 Smaller Members of the Solar System

Most of the planets are accompanied by one or more moons ; only Mercury and Venus move through space alone. There are more than 210 known moons orbiting planets and dwarf planets, and undoubtedly many other small ones remain undiscovered. The largest of the moons are as big as small planets and just as interesting. In addition to our Moon, they include the four largest moons of Jupiter (called the Galilean moons, after their discoverer) and the largest moons of Saturn and Neptune (confusingly named Titan and Triton).

Each of the giant planets also has rings made up of countless small bodies ranging in size from mountains to mere grains of dust, all in orbit about the equator of the planet. The bright rings of Saturn are, by far, the easiest to see. They are among the most beautiful sights in the solar system.   But, all four ring systems are interesting to scientists because of their complicated forms, influenced by the pull of the moons that also orbit these giant planets.

The solar system has many other less-conspicuous members. Another group is the  asteroids , rocky bodies that orbit the Sun like miniature planets, mostly in the space between Mars and Jupiter (although some do cross the orbits of planets like Earth). Most asteroids are remnants of the initial population of the solar system that existed before the planets themselves formed. Some of the smallest moons of the planets, such as the moons of Mars, are very likely captured asteroids.

Another class of small bodies is composed mostly of ice, made of frozen gases such as water, carbon dioxide, and carbon monoxide; these objects are called  comets . Comets also are remnants from the formation of the solar system, but they were formed and continue (with rare exceptions) to orbit the Sun in distant, cooler regions—stored in a sort of cosmic deep freeze. This is also the realm of the larger icy worlds, called dwarf planets.

Finally, there are countless grains of broken rock, which we call cosmic dust, scattered throughout the solar system. When these particles enter Earth’s atmosphere (as millions do each day), they burn up, producing a brief flash of light in the night sky known as a meteor  (meteors are often referred to as shooting stars). Occasionally, some larger chunk of rocky or metallic material survives its passage through the atmosphere and lands on Earth. Any piece that strikes the ground is known as a  meteorite . You can see meteorites on display in many natural history museums and can sometimes even purchase pieces of them from gem and mineral dealers.

17.2.3 A Scale Model of the Solar System

Astronomy often deals with dimensions and distances that far exceed our ordinary experience. What does 1.4 billion kilometers—the distance from the Sun to Saturn—really mean to anyone? It can be helpful to visualize such large systems in terms of a scale model.

In our imaginations, let us build a scale model of the solar system, adopting a scale factor of 1 billion (10 9 )—that is, reducing the actual solar system by dividing every dimension by a factor of 10 9 . Earth, then, has a diameter of 1.3 centimeters, about the size of a grape. The Moon is a pea orbiting this at a distance of 40 centimeters, or a little more than a foot away. The Earth-Moon system fits into a standard backpack.

In this model, the Sun is nearly 1.5 meters in diameter, about the average height of an adult, and our Earth is at a distance of 150 meters—about one city block—from the Sun. Jupiter is five blocks away from the Sun, and its diameter is 15 centimeters, about the size of a very large grapefruit. Saturn is 10 blocks from the Sun; Uranus, 20 blocks; and Neptune, 30 blocks. Pluto, with a distance that varies quite a bit during its 249-year orbit, is currently just beyond 30 blocks and getting farther with time. Most of the moons of the outer solar system are the sizes of various kinds of seeds orbiting the grapefruit, oranges, and lemons that represent the outer planets.

In our scale model, a human is reduced to the dimensions of a single atom, and cars and spacecraft to the size of molecules. Sending the Voyager spacecraft to Neptune involves navigating a single molecule from the Earth–grape toward a lemon 5 kilometers away with an accuracy equivalent to the width of a thread in a spider’s web.

If that model represents the solar system, where would the nearest stars be? If we keep the same scale, the closest stars would be tens of thousands of kilometers away. If you built this scale model in the city where you live, you would have to place the representations of these stars on the other side of Earth or beyond.

By the way, model solar systems like the one we just presented have been built in cities throughout the world. In Sweden, for example, Stockholm’s huge Globe Arena has become a model for the Sun, and Pluto is represented by a 12-centimeter sculpture in the small town of Delsbo, 300 kilometers away. Another model solar system is in Washington on the Mall between the White House and Congress (perhaps proving they are worlds apart?).

If you are using an offline version of this text, access the quiz for section 17.2 via the QR code.

17.3 Composition and Structure of Planets [2]

The fact that there are two distinct kinds of planets—the rocky terrestrial planets and the gas-rich Jovian planets—leads us to believe that they formed under different conditions. Certainly their compositions are dominated by different elements . Let us look at each type in more detail.

17.3.1 The Giant Planets

The two largest planets,  Jupiter  and  Saturn , have nearly the same chemical makeup as the Sun; they are composed primarily of the two elements hydrogen and helium, with 75% of their mass being hydrogen and 25% helium. On Earth, both hydrogen and helium are gases, so Jupiter and Saturn are sometimes called gas planets. But, this name is misleading. Jupiter and Saturn are so large that the gas is compressed in their interior until the hydrogen becomes a liquid. Because the bulk of both planets consists of compressed, liquefied hydrogen, we should really call them liquid planets.

Under the force of gravity, the heavier elements sink toward the inner parts of a liquid or gaseous planet. Both Jupiter and Saturn, therefore, have cores composed of heavier rock, metal, and ice, but we cannot see these regions directly. In fact, when we look down from above, all we see is the atmosphere with its swirling clouds. We must infer the existence of the denser core inside these planets from studies of each planet’s gravity.

Uranus  and  Neptune are much smaller than Jupiter and Saturn, but each also has a core of rock, metal, and ice. Uranus and Neptune were less efficient at attracting hydrogen and helium gas, so they have much smaller atmospheres in proportion to their cores.

Chemically, each giant planet is dominated by hydrogen and its many compounds. Nearly all the oxygen present is combined chemically with hydrogen to form water (H 2 O). Chemists call such a hydrogen-dominated composition  reduced . Throughout the outer solar system, we find abundant water (mostly in the form of ice) and reducing chemistry.

17.3.2 The Terrestrial Planets

The terrestrial planets are quite different from the giants. In addition to being much smaller, they are composed primarily of rocks and metals. These, in turn, are made of elements that are less common in the universe as a whole. The most abundant rocks, called silicates , are made of silicon and oxygen, and the most common metal is iron. We can tell from their densities that  Mercury  has the greatest proportion of metals (which are denser) and the Moon has the lowest.  Earth ,  Venus , and  Mars  all have roughly similar bulk compositions: about one third of their mass consists of iron-nickel or iron-sulfur combinations; two thirds is made of silicates. Because these planets are largely composed of oxygen compounds (such as the silicate minerals of their crusts), their chemistry is said to be  oxidized .

When we look at the internal structure of each of the terrestrial planets, we find that the densest metals are in a central core, with the lighter silicates near the surface. If these planets were liquid, like the giant planets, we could understand this effect as the result the sinking of heavier elements due to the pull of gravity. This leads us to conclude that, although the terrestrial planets are solid today, at one time they must have been hot enough to melt.

Differentiation  is the process by which gravity helps separate a planet’s interior into layers of different compositions and densities. The heavier metals sink to form a core, while the lightest minerals float to the surface to form a crust. Later, when the planet cools, this layered structure is preserved. In order for a rocky planet to differentiate, it must be heated to the melting point of rocks, which is typically more than 1300 K.

17.3.3 Moons, Asteroids, and Comets

Chemically and structurally, Earth’s Moon is like the terrestrial planets, but most moons are in the outer solar system, and they have compositions similar to the cores of the giant planets around which they orbit. The three largest moons—Ganymede and Callisto in the Jovian system, and  Titan in the Saturnian system—are composed half of frozen water, and half of rocks and metals. Most of these moons differentiated during formation, and today they have cores of rock and metal, with upper layers and crusts of very cold and—thus very hard—ice.

Most of the asteroids and comets , as well as the smallest moons , were probably never heated to the melting point. However, some of the largest asteroids, such as  Vesta , appear to be differentiated; others are fragments from differentiated bodies. Many of the smaller objects seem to be fragments or rubble piles that are the result of collisions. Because most asteroids and comets retain their original composition, they represent relatively unmodified material dating back to the time of the formation of the solar system. In a sense, they act as chemical fossils, helping us to learn about a time long ago whose traces have been erased on larger worlds.

17.3.4 Temperatures: Going to Extremes

Generally speaking, the farther a planet or moon is from the Sun, the cooler its surface. The planets are heated by the radiant energy of the Sun, which gets weaker with the square of the distance. You know how rapidly the heating effect of a fireplace or an outdoor radiant heater diminishes as you walk away from it; the same effect applies to the Sun.  Mercury , the closest planet to the Sun, has a blistering surface temperature that ranges from 280–430 °C on its sunlit side, whereas the surface temperature on  Pluto is only about –220 °C, colder than liquid air.

Mathematically, the temperatures decrease approximately in proportion to the square root of the distance from the Sun. Pluto is about 30 AU at its closest to the Sun (or 100 times the distance of Mercury) and about 49 AU at its farthest from the Sun. Thus, Pluto’s temperature is less than that of Mercury by the square root of 100, or a factor of 10: from 500 K to 50 K.

In addition to its distance from the Sun, the surface temperature of a planet can be influenced strongly by its atmosphere . Without our atmospheric insulation (the greenhouse effect, which keeps the heat in), the oceans of Earth would be permanently frozen. Conversely, if Mars once had a larger atmosphere in the past, it could have supported a more temperate climate than it has today. Venus is an even more extreme example, where its thick atmosphere of carbon dioxide acts as insulation, reducing the escape of heat built up at the surface, resulting in temperatures greater than those on Mercury. Today, Earth is the only planet where surface temperatures generally lie between the freezing and boiling points of water. As far as we know, Earth is the only planet to support life.

17.3.5 Dating Planetary Surfaces [3]

How do we know the age of the surfaces we see on planets and moons? If a world has a surface (as opposed to being mostly gas and liquid), astronomers have developed some techniques for estimating how long ago that surface solidified. Note that the age of these surfaces is not necessarily the age of the planet as a whole. On geologically active objects (including Earth), vast outpourings of molten rock or the erosive effects of water and ice, which we call planet weathering , have erased evidence of earlier epochs and present us with only a relatively young surface for investigation.

One way to estimate the age of a surface is by counting the number of impact  craters . This technique works because the rate at which impacts have occurred in the solar system has been roughly constant for several billion years. Thus, in the absence of forces to eliminate craters, the number of craters is simply proportional to the length of time the surface has been exposed. This technique has been applied successfully to many solid planets and moons .

Bear in mind that crater counts can tell us only the time since the surface experienced a major change that could modify or erase preexisting craters. Estimating ages from crater counts is a little like walking along a sidewalk in a snowstorm after the snow has been falling steadily for a day or more. You may notice that in front of one house the snow is deep, while next door the sidewalk may be almost clear. Do you conclude that less snow has fallen in front of Ms. Jones’ house than Mr. Smith’s? More likely, you conclude that Jones has recently swept the walk clean and Smith has not. Similarly, the numbers of craters indicate how long it has been since a planetary surface was last “swept clean” by ongoing lava flows or by molten materials ejected when a large impact happened nearby.

Still, astronomers can use the numbers of craters on different parts of the same world to provide important clues about how regions on that world evolved. On a given planet or moon, the more heavily cratered terrain will generally be older (that is, more time will have elapsed there since something swept the region clean).

17.3.6 Radioactive Rocks

Another way to trace the history of a solid world is to measure the age of individual rocks. After samples were brought back from the Moon  by Apollo astronauts, the techniques that had been developed to date rocks on Earth were applied to rock samples from the Moon to establish a geological chronology for the Moon. Furthermore, a few samples of material from the Moon, Mars, and the large asteroid  Vesta have fallen to Earth as meteorites and can be examined directly.

Scientists measure the age of rocks using the properties of natural  radioactivity . Around the beginning of the twentieth century, physicists began to understand that some atomic nuclei are not stable but can split apart (decay) spontaneously into smaller nuclei. The process of radioactive decay involves the emission of particles such as electrons , or of radiation in the form of gamma rays .

For any one radioactive nucleus, it is not possible to predict when the decay process will happen. Such decay is random in nature, like the throw of dice: as gamblers have found all too often, it is impossible to say just when the dice will come up 7 or 11. But, for a very large number of dice tosses, we can calculate the odds that 7 or 11 will come up. Similarly, if we have a very large number of radioactive atoms of one type (say, uranium), there is a specific time period, called its  half-life , during which the chances are fifty-fifty that decay will occur for any of the nuclei.

A particular nucleus may last a shorter or longer time than its half-life, but in a large sample, almost exactly half of the nuclei will have decayed after a time equal to one half-life. Half of the remaining nuclei will have decayed after two half-lives pass, leaving only one half of a half—or one quarter—of the original sample.

If you had 1 gram of pure radioactive nuclei with a half-life of 100 years, then after 100 years you would have 1/2 gram; after 200 years, 1/4 gram; after 300 years, only 1/8 gram; and so forth. However, the material does not disappear. Instead, the radioactive atoms are replaced with their decay products. Sometimes the radioactive atoms are called  parents  and the decay products are called  daughter elements.

In this way, radioactive elements with half-lives we have determined can provide accurate nuclear clocks. By comparing how much of a radioactive parent element is left in a rock to how much of its daughter products have accumulated, we can learn how long the decay process has been going on and hence how long ago the rock formed. The following table summarizes the decay reactions used most often to date lunar and terrestrial rocks.

Table 17.3: Radioactive decay reaction used to date rocks. The number after each element is its atomic weight, equal to the number of protons plus neutrons in its nucleus. This specifies the isotope of the element, different isotopes of the same element differ in the number of neutrons.

When astronauts first flew to the Moon, one of their most important tasks was to bring back lunar rocks for radioactive age-dating. Until then, astronomers and geologists had no reliable way to measure the age of the lunar surface. Counting craters had let us calculate relative ages (for example, the heavily cratered lunar highlands were older than the dark lava plains), but scientists could not measure the actual age in years. Some thought that the ages were as young as those of Earth’s surface, which has been resurfaced by many geological events. For the Moon’s surface to be so young would imply active geology on our satellite. Only in 1969, when the first Apollo samples were dated, did we learn that the Moon is an ancient, geologically dead world. Using such dating techniques, we have been able to determine the ages of both Earth and the Moon: each was formed about 4.5 billion years ago (although, as we shall see, Earth probably formed earlier than the Moon).

We should also note that the decay of radioactive nuclei generally releases energy in the form of heat. Although the energy from a single nucleus is not very large (in human terms), the enormous numbers of radioactive nuclei in a planet or moon (especially early in its existence) can be a significant source of internal energy for that world. Geologists estimate that about half of Earth’s current internal heat budget comes from the decay of radioactive isotopes in its interior.

If you are using an offline version of this text, access the quiz for section 17.3 via the QR code.

17.4 Origin of the Solar System [4]

Much of astronomy is motivated by a desire to understand the origin of things: to find at least partial answers to age-old questions of where the universe , the Sun, Earth, and we ourselves came from. Each planet and moon is a fascinating place that may stimulate our imagination as we try to picture what it would be like to visit. Taken together, the members of the solar system preserve patterns that can tell us about the formation of the entire system. As we begin our exploration of the planets, we want to introduce our modern picture of how the solar system formed.

The recent discovery of thousands of planets in orbit around other stars has shown astronomers that many exoplanetary systems can be quite different from our own solar system. For example, it is common for these systems to include planets intermediate in size between our terrestrial and giant planets. These are often called  superearths . Some exoplanet systems even have giant planets close to the star, reversing the order we see in our system.

17.4.1 Looking for Patterns

One way to approach our question of origin is to look for regularities among the planets. We found, for example, that all the planets lie in nearly the same plane and revolve in the same direction around the Sun. The Sun also spins in the same direction about its own axis. Astronomers interpret this pattern as evidence that the Sun and planets formed together from a spinning cloud of gas and dust that we call the  solar nebula .

The composition of the planets gives another clue about origins. Spectroscopic analysis allows us to determine which elements are present in the Sun and the planets. The Sun has the same hydrogen-dominated composition as Jupiter and Saturn, and therefore appears to have been formed from the same reservoir of material. In comparison, the terrestrial planets and our Moon are relatively deficient in the light gases and the various ices that form from the common elements oxygen, carbon, and nitrogen. Instead, on Earth and its neighbors, we see mostly the rarer heavy elements such as iron and silicon. This pattern suggests that the processes that led to planet formation in the inner solar system must somehow have excluded much of the lighter materials that are common elsewhere. These lighter materials must have escaped, leaving a residue of heavy stuff.

The reason for this is not hard to guess, bearing in mind the heat of the Sun. The inner planets and most of the asteroids are made of rock and metal, which can survive heat, but they contain very little ice or gas, which evaporate when temperatures are high (to see what we mean, just compare how long a rock and an ice cube survive when they are placed in the sunlight). In the outer solar system, where it has always been cooler, the planets and their moons, as well as icy dwarf planets and comets , are composed mostly of ice and gas.

17.4.2 The Evidence from Far Away

A second approach to understanding the origins of the solar system is to look outward for evidence that other systems of planets are forming elsewhere. We cannot look back in time to the formation of our own system, but many stars in space are much younger than the Sun. In these systems, the processes of planet formation might still be accessible to direct observation. We observe that there are many other “ solar nebulas ” or  circumstellar disks —flattened, spinning clouds of gas and dust surrounding young stars. These disks resemble our own solar system’s initial stages of formation billions of years ago.

17.4.3 Building Planets

Circumstellar disks are a common occurrence around very young stars, suggesting that disks and stars form together. Astronomers can use theoretical calculations to see how solid bodies might form from the gas and dust in these disks as they cool. These models show that material begins to coalesce first by forming smaller objects, precursors of the planets, which we call  planetesimals .

Today’s fast computers can simulate the way millions of planetesimals, probably no larger than 100 kilometers in diameter, might gather together under their mutual gravity to form the planets we see today. We are beginning to understand that this process was a violent one, with planetesimals crashing into each other and sometimes even disrupting the growing planets themselves. As a consequence of those violent impacts (and the heat from radioactive elements in them), all the planets were heated until they were liquid and gas, and therefore differentiated, which helps explain their present internal structures.

The process of impacts and collisions in the early solar system was complex and, apparently, often random. The solar nebula model can explain many of the regularities we find in the solar system, but the random collisions of massive collections of planetesimals could be the reason for some exceptions to the “rules” of solar system behavior. For example, why do the planets Uranus and Pluto spin on their sides? Why does Venus spin slowly and in the opposite direction from the other planets? Why does the composition of the Moon resemble Earth in many ways and yet exhibit substantial differences? The answers to such questions probably lie in enormous collisions that took place in the solar system long before life on Earth began.

Today, some 4.5 billion years after its origin, the solar system is—thank goodness—a much less violent place. However, some planetesimals have continued to interact and collide, and their fragments move about the solar system as roving “transients” that can make trouble for the established members of the Sun’s family, such as our own Earth.

If you are using an offline version of this text, access the quiz for section 17.4 via the QR code.

Our solar system currently consists of the Sun, eight planets, five dwarf planets, nearly 200 known moons , and a host of smaller objects. The planets can be divided into two groups: the inner terrestrial planets and the outer giant planets. Smaller members of the solar system include asteroids (including the dwarf planet Ceres), which are rocky and metallic objects found mostly between Mars and Jupiter; comets , which are made mostly of frozen gases and generally orbit far from the Sun; and countless smaller grains of cosmic dust. When a meteor survives its passage through our atmosphere and falls to Earth, we call it a meteorite .

The ages of the surfaces of objects in the solar system can be estimated by counting craters: on a given world, a more heavily cratered region will generally be older than one that is less cratered. We can also use samples of rocks with radioactive elements in them to obtain the time since the layer in which the rock formed last solidified. The half-life of a radioactive element is the time it takes for half the sample to decay; we determine how many half-lives have passed by how much of a sample remains the radioactive element and how much has become the decay product. In this way, we have estimated the age of the Moon and Earth to be roughly 4.5 billion years.

Regularities among the planets have led astronomers to hypothesize that the Sun and the planets formed together in a giant, spinning cloud of gas and dust called the solar nebula . Astronomical observations show tantalizingly similar circumstellar disks around other stars. Within the solar nebula, material first coalesced into planetesimals ; many of these gathered together to make the planets and moons. The remainder can still be seen as comets and asteroids. Probably all planetary systems have formed in similar ways, but many exoplanet systems have evolved along quite different paths.

If you are using an offline version of this text, access the quiz for chapter 17 via the QR code.

Text References

Parts of this chapter are from OpenStax’s Astronomy (chapter 7) . 2016. CC BY 4.0 .

Chapter 17 Origin of Earth and the Solar System ( CC BY 4.0)  by Karla Panchuk was added from Earle, Steven (2019) Physical Geology, 2nd edition. BC Campus https://opentextbc.ca/physicalgeology2ed/chapter/22-1-starting-with-a-big-bang

Figure References

Figure 17.1: The big bang. NASA/WMAP Science Team. 2006. Public domain. https://en.wikipedia.org/wiki/File:CMB_Timeline300_no_WMAP.jpg

Figure 17.2: Cosmic microwave background (CMB) map of the sky, a baby picture of the universe. NASA / WMAP Science Team. 2012. Public domain. https://commons.wikimedia.org/wiki/File:Ilc_9yr_moll4096.png

Figure 17.3: Doppler effect. Charly Whisky. 2007. CC BY-SA 3.0 . https://commons.wikimedia.org/wiki/File%3ADopplerfrequenz.gif

Figure 17.4: Red shift in light from the supercluster BAS11 compared to the sun’s light. Kindred Grey. 2022. CC BY 4.0 . Includes Duck by parkjisun from Noun Project ( Noun Project license ).

Figure 17.5: Astronauts on the Moon. NASA Johnson Space Center; Restored by Bammesk. 1971. Public domain. https://en.wikipedia.org/wiki/File:AS15-88-11866_-_Apollo_15_flag,_rover,_LM,_Irwin_-_restoration1.jpg

Figure 17.6: Orbits of the planets. Arabik4892. 2022. CC BY-SA 4.0 . https://commons.wikimedia.org/wiki/File:Planet_Orbits.jpg

Figure 17.7: Surface of Mercury. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington. 2009. Public domain. https://commons.wikimedia.org/wiki/File:Mercury_Double-Ring_Impact_Basin.png

Figure 17.8: The four giant planets. Solar System Exploration, NASA. 2008. Public domain. https://commons.wikimedia.org/wiki/File:Gas_planet_size_comparisons.jpg

Figure 17.9: This intriguing image from the New Horizons spacecraft, taken when it flew by the dwarf planet Pluto in July 2015, shows some of its complex surface features. NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute. 2015. Public domain. https://en.wikipedia.org/wiki/File:Pluto-01_Stern_03_Pluto_Color_TXT.jpg

Figure 17.10: Saturn and its A, B, and C rings in visible and (inset) infrared light. NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic (ISS), NASA/JPL-Caltech/University of Arizona/CNRS/LPG-Nantes (VIMS). 2019. Public domain. https://commons.wikimedia.org/wiki/File:PIA23170-Saturn-Rings-IR-Map-20190613.jpg

Figure 17.11: Asteroid Eros. NASA/JPL/JHUAPL. 2000. Public domain. https://commons.wikimedia.org/wiki/File:Eros_-_PIA02923_(color).jpg

Figure 17.12: Comet Churyumov-Gerasimenko (67P). ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA. 2014. CC BY-SA 4.0 . https://commons.wikimedia.org/wiki/File:Comet_67P_True_color.jpg

Figure 17.13: Jupiter with its moon Europa on the left. NASA, ESA, STScI, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley) and the OPAL team. 2020. Public domain. https://commons.wikimedia.org/wiki/File:Jupiter_and_Europa_2020.tiff

Figure 17.14: Jupiter’s moon Ganymede. NOAA. 2009. Public domain. https://commons.wikimedia.org/wiki/File:Moon_Ganymede_by_NOAA.jpg

Figure 17.15: Our cratered Moon. NASA/Goddard/Arizona State University. 2011. Public domain. https://www.nasa.gov/mission_pages/LRO/news/lro-farside.html

Figure 17.16: Radioactive decay. Andrew Fraknoi, David Morrison, and Sidney Wolff. 2015. CC BY 4.0 . https://en.wikipedia.org/wiki/File:OSC_Astro_07_03_Decay_(1).jpg

Figure 17.17: NASA artist’s conception of various planet formation processes, including exocomets and other planetesimals, around Beta Pictoris, a very young type A V star. NASA/FUSE/Lynette Cook. 2007. Public domain. https://commons.wikimedia.org/wiki/File:NASA-ExocometsAroundBetaPictoris-ArtistView.jpg

Figure 17.18: Atlas of Planetary Nurseries. NASA/ESA and L. Ricci (ESO). 2009. CC BY 4.0 . https://esahubble.org/copyright/

• Source: OpenStax Astronomy (CC BY). Access for free at https://openstax.org/books/astronomy-2e/pages/7-1-overview-of-our-planetary-system ↵
• Source: OpenStax Astronomy (CC BY). Access for free at https://openstax.org/books/astronomy/pages/7-2-composition-and-structure-of-planets ↵
• Source: OpenStax Astronomy (CC BY). Access for free at https://openstax.org/books/astronomy/pages/7-3-dating-planetary-surfaces ↵
• Source: OpenStax Astronomy (CC BY). Access for free at https://openstax.org/books/astronomy/pages/7-4-origin-of-the-solar-system ↵

All of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.

The generic term for a group of planets and other bodies circling a star is planetary system. Our planetary system is the only one officially called “solar system,” because our Sun is sometimes called Sol.

A large astronomical body that is neither a star nor a stellar remnant.

The measure of the vibrational (kinetic) energy of a substance.

Originating or existing outside the solar system.

The theory that the Universe started with a expansive explosion. Shortly after, elements were created (mostly hydrogen) and galaxies started to form.

A process inside stars where smaller atoms combine and form larger atoms.

The generic term for a group of planets and other bodies circling a star.

The process of atoms breaking down randomly and spontaneously.

Any planet beyond our solar system.

A group of all atoms with a specific number of protons, having specific, universal, and unique properties.

The distance that light can travel through space in a year. One light year is 9.4607 × 10^12 km.

Radiation left over from the an early stage in the development of the universe at the time when protons and neutrons were recombining to form atoms.

A gravitationally-bound system of stars and interstellar matter.

The increase in wavelength of light resulting from the fact that the source of the light is moving away from the observer.

The distance between any two repeating portions of a wave (e.g., two successive wave crests).

to move in a circular or curving course or orbit. Not to be confused with rotate, when something spins on an axis

An object that orbits a planet or something else that is not a star. Besides planets, moons can circle dwarf planets, large asteroids, and other bodies.

A small rocky body orbiting the sun.

a celestial object consisting of a nucleus of ice and dust and, when near the Sun, a “tail” of gas and dust particles pointing away from the Sun

A small planetary-mass object that is in direct orbit of the Sun – something smaller than any of the eight classical planets, but still a world in its own right.

The layers of gases surrounding a planet or other celestial body.

To move in a circular or curving course or orbit. Not to be confused with rotate, when something spins on an axis.

To spin on an axis. Not to be confused with revolve, when something moves in a circular or curving course or orbit.

A bowl-shaped depression, or hollowed-out area, produced by the impact of a meteorite, volcanic activity, or an explosion.

A landform that rises above its surrounding area.

Place where lava is erupted at the surface.

A circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun.

A spherical layer of icy objects surrounding our Sun; likely occupies space at a distance between about 2,000 and 100,000 astronomical units (AU) from the Sun.

The gases that are part of the Earth, which are mainly nitrogen and oxygen.

A small body of matter from outer space that enters the Earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.

A stoney and/or metallic object from our solar system which was never incorporated into a planet and has fallen onto Earth. Meteorite is used for the rock on Earth, meteoroid for the object in space, and meteor as the object travels in Earth's atmosphere.

The branch of science which deals with celestial objects, space, and the physical universe as a whole.

A straight line passing from side to side through the center of a body or figure, especially a circle or sphere.

Reduction involves a half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons.

Mineral group in which the silica tetrahedra, SiO4-4, is the building block.

A solid material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity.

Oxidation is the loss of electrons or an increase in the oxidation state of a chemical or atoms within it.

In planetary science, differentiation is the process of separating out the different components within a planetary body as a consequence of their physical or chemical behavior (e.g. density and chemical affinities).

An AU (or astronomical unit) is the average distance from Earth to the Sun.

The kelvin, symbol K, is the SI base unit of temperature. Absolute zero is 0 K, the equivalent of −273.15°C.

Breaking down rocks into small pieces by chemical or mechanical means.

A stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids.

A penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically shorter than those of X-rays.

A radioactive atom that can and will decay.

The atom that is made after a radioactive decay.

Of or pertaining to an exoplanet, a planet outside the solar system.

Rotating, flattened disk of gas and dust from which the solar system originated.

Turn from liquid into vapor.

A body that could or did come together with many others under gravitation to form a planet.

The calculated amount of time that half of the mass of an original (parent) radioactive isotope breaks down into a new (daughter) isotope.

Introduction to Earth Science Copyright © 2023 by Laura Neser is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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October 1, 1952

The Origin of the Earth

The emergence of the theory that the solar system coagulated from a vast cloud of dust has led to a new inquiry into the chemical history of our planet

By Harold C. Urey

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Origin and Structure of the Earth

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DR. JEFFREY'S book on the earth will be very welcome to the many who are interested in the larger dynamical aspects of our planet, in its present and past states. The book may be divided roughly into three nearly equal parts, dealing respectively with the origin and past history of the earth (considered as a basis for conclusions about its present condition), the theory of isostasy and of the surface features, and, finally, various miscellaneous subjects-seismology, the figures of the earth and moon, tidal friction, and the variation of latitude. Despite the generality of the title given to the book, many branches of geophysics are not touched on at all-terrestrial magnetism and electricity, general tidal theory, and meteorology. This was almost inevitable in a book of comparatively small size, particularly since its aim is not to be merely descriptive, but rather to give in some detail the mathematical reasons for the hypotheses adopted.

The Earth: its Origin, History, and Physical Constitution.

By Dr. Harold Jeffreys. Pp. x + 278. (Cambridge: at the University Press, 1924.) 16 s . net.

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The Earth: Origin, Evolution and Structure | Essay | Geography

Here is an essay on the ‘Earth’ for class 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on the ‘Earth’ especially written for school and college students.

Essay on the Earth

Essay Contents:

• Essay on Position of the Earth

Essay # 1. Origin of the Earth:

The earth is believed to be formed from a small part of the sun and most of the theories concerned with the origin of the earth emphasize that the planet originated as a hot gaseous mass which upon cooling, turned first into liquid and then solid. An early theory was put forth by Kant, which is popularly known as the gaseous hypothesis.

A more popular theory was advanced by Laplace which is called the nebular hypothesis. This theory considers earth being formed through the solidifi­cation of the mass of a ring thrown away by a cooling and rotating nebula (sun) and this ring was one of the nine such rings which formed various planets.

A more plausible theory put forth by Jeans and Jeffreys assumes origin of the earth on the basis of the presence of two nebulae. This theory is called the tidal hypothesis and it belongs to the group of the binary star theories. According to this theory, a large nebula wandering in the space came very close to another smaller nebula which is sun and its gravitational pull caused a huge tidal upsurge of matter on the surface of the smaller nebula.

As the larger nebula moved away from the smaller one in its journey, the matter rising as a tidal wave from the surface of the smaller nebula was pulled towards it and was drawn to a distance from which it could not come back to the parent body. However, it could not follow the large nebula also and as the larger nebula went away the rising tongue of matter was detached from the smaller nebula.

On cooling, this matter condensed to form the planets, including the earth, and the planets thus formed started revolving around the sun. This hypothesis is consid­ered to be highly probable and close to reality. The cigar-shaped arrangement of the planets going away from the sun, with the smallest planets located closest and farthest from the sun and the larger ones occupy­ing intermediate positions, strengthens this view.

The above theory considers that the earth origi­nated as a hot mass and cooled slowly to develop a solid crust and the inner part of the earth from which the heat loss has been slow is still liquid. Some of the other theories also assume that the earth originated as a mass of solid matter and it is the decay of the radioactive elements in its interior and the pressure of the overlying strata due to which the interior of the earth is in liquid state.

In whatever state the earth might have come into existence, the aggregation of the mass has led to a differentiation of the matter forming it on the basis of the density. The denser mat­ter forms the central part of the earth and the surface rocks are made up of the lighter materials.

The rocks forming the surface layer of the earth which are rich in lighter minerals such as aluminium are called sial (silica and aluminium) while the denser rocks forming the inner layers of the earth are called sima (silica and magnesium) and nife (nickel and iron).

This dif­ferentiation of various elements of the earth has been responsible for the layered structure of the earth. The formation of the solid crust of the earth took place sometimes 4.6 billion years ago and it is taken as the beginning of the history of the earth as such.

Modern Theories:

The most popular theory of our universe’s origin centres on a cosmic cataclysm unmatched in history—the big bang. This theory was born out of observation that other galaxies are moving away from our own at great speed, in all directions, as if they all had been propelled by an ancient explosive force.

Before the big bang, scientists believe, that the entire vastness of the universe, including all of its matter and radiations, was compressed into a hot, dense mass just a few millimetres across. This nearly incomprehensible state is theorized to have existed for just a fraction of the first second of time.

Big bang proponents suggest that some 10-20 billion years ago, a massive blast allowed all the universe’s known matter and energy—even space and time themselves—to spring from some ancient and unknown type of energy.

The theory maintains that, in the instant—a trillion-trillionth of a second—after the big bang, the universe expanded with incomprehensible speed from its pebble-size origin to astronomical scope. Expansion has apparently continued, but much more slowly, over the ensuing billions of years.

Scientists can’t be sure exactly how the universe evolved after the big bang. Many believe that as time passed and matter cooled, more diverse kinds of atoms began to form, and they eventually condensed into the stars and galaxies of our existing universe.

Big Bang Theory:

The Big Bang theory considers the following stages in the development of the universe:

(i) In the beginning, all matter forming the universe existed at one place in the form of a ‘tiny ball’ (singular atom) with an unimaginably small volume, infinite tempera­ture and infinite density.

(ii) At the ‘Big Bang’, the tiny ball exploded violently. This led to a huge expansion. It is now generally accepted that the event of big bang took place 13.7 billion years ago. The expansion is continued even today.

As it grew, some energy was converted into matter. There was particularly rapid expansion within fractions of a second after the bang. Thereafter, the expansion has slowed down. Within first three minutes of the Big Bang event, the first atom began to form.

(iii) Within 300,000 years from the Big Bang, temperature dropped to 4,500 K (Kelvin) and gave rise to atomic matter. The universe became transparent.

Origin of the Theory:

A Belgian priest named Georges Lemaitre first suggested the big bang theory in the 1920s when he theorized that the universe began from a single primordial atom. The idea subsequently received major boosts by Edwin Hubble’s observations that galaxies are speeding away from us in all directions, and from the discovery of cosmic microwave radia­tion by Arno Penzias and Robert Wilson.

The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the big bang. The radiation akin to that is used to transmit TV signals via antennas. But it is the oldest known radiation and may hold many secrets about the universe’s earliest moments.

The big bang theory leaves several major ques­tions unanswered. One is the original cause of the big bang itself. Several answers have been proposed to address this fundamental question, but none has been proven—and even adequately testing them has proved to be a formidable challenge.

Essay # 2. Evolution of the Earth:

The earth has a layered structure. From the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform. The atmospheric matter has the least density. From the surface to deeper depths, the earth’s interior has different zones and each of these contains materials with different characteristics.

Evolution of Atmosphere and Hydrosphere :

The present composition of earth’s atmosphere is chiefly contributed by nitrogen and oxygen. There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of primordial atmos­phere. In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere. Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.

The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds. This happened not only in case of the earth, but also in all the terrestrial planets, which were sup­posed to have lost their primordial atmosphere through the impact of solar winds. During the cooling of the earth, gases and water vapour were released from the interior solid earth.

This started the evolution of the present atmosphere. The early atmosphere largely con­tained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen. The process through which the gases were outpoured from the inte­rior is called degassing. Continuous volcanic eruptions contributed water vapour and gases to the atmosphere.

As the earth cooled, the water vapour released started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains. The rainwater falling onto the surface got collected in the depressions to give rise to oceans.

The earth’s oceans were formed within 500 million years from the formation of the earth. This tells us that the oceans are as old as 4,000 million years. Sometime around 3,800 million years ago, life began to evolve. However, around 2,500-3,000 million years ago, the process of photosynthesis got evolved. Life was confined to the oceans for a long time.

Oceans began to have the contribution of oxygen through the process of photosynthesis. Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood the atmosphere.

Essay # 3. Size and Shape of the Earth:

Earth, with an average distance of 92,955,820 miles (149,597,890 km) from the sun, is the third planet and one of the most unique planets in the solar system. It was formed around 4.5-4.6 billion years ago and is the only planet known to sustain life. This is because factors like its atmospheric composition and physical properties such as the presence of water, over 70.8% of the planet allows life to thrive.

Earth is also unique however, because it is the largest of the terrestrial planets (one that is com­posed of a thin layer of rocks as opposed to those that are mostly made up of gases like Jupiter or Saturn) based on its mass, density, and diameter. Earth is also the fifth largest planet in the entire solar system.

Earth’s circumference and diameter differ because its shape is classified as an oblate spheroid or ellip­soid, instead of a true sphere. This means that instead of being of equal circumference in all areas, the poles are squished, resulting in a bulge at the equator, and thus a larger circumference and diameter there.

The equatorial bulge at Earth’s equator is measured at 26.5 miles (42.72 km) and is caused by the planet’s rotation and gravity. Gravity itself causes planets and other celestial bodies to contract and form a sphere. This is because it pulls all the mass of an object as close to the centre of gravity (the Earth’s core in this case) as possible.

Because Earth rotates, this sphere is distorted by the centrifugal force. This is the force that causes objects to move outward away from the centre of gravity. Therefore, as the Earth rotates, centrifugal force is greatest at the equator so it causes a slight outward bulge there, giving that region a larger circumference and diameter.

Essay # 4. Structure of Earth:

i. It is almost round in shape and has a diameter of 1.27 x 10 4 km.

ii. Its real shape is a sphere flattened at the poles and buldged in the plane normal to the poles.

iii. The earth’s inner core is a solid mass made of iron and nickel and the next outer core is melted state of iron and nickel. The outermost portion is made of rocks.

iv. The existence of blue green algae indicates beginning of photosynthesis at least 3 x 10 9 years ago. As a result of photosynthesis, the level of O 2 and O 3 is increased in the atmosphere which block the ultra violet (UV) solar radiation coming from the ‘sun’. Half the earth is lit by the sunlight at a time. It reflects one-third of the sunlight that falls on it, is known as earth’s albedo.

v. The length of days and nights keep changing because the earth is spinning about its axis which is inclined at an angle of 23.5°.

Essay # 5. Motions of the Earth:

The earth has two types of motions, namely rotation and revolution:

i. Rotation:

The Earth rotates on its axis, from west to east like a top. This motion is called Rotation of the Earth.

ii. Revolution:

While rotating on its axis, the earth also goes around the sun in an elliptical path and completes one round in 365 days and 6 hours. The elliptical path traced by the earth is called its orbit. This motion of the earth is called revolution.

Essay # 6. Latitudinal and Longitudinal Measurements of the Earth:

A key geographical question throughout the human experience has been, ‘Where am I?’ In classical Greece and China, attempts were made to create logi­cal grid systems of the world to answer this question. The ancient Greek geographer Ptolemy created a grid system and listed the coordinates for places throughout the known world in his book Geography. But it wasn’t until the middle ages that the latitude and longitude system was developed and implemented. This system is written in degrees, using the symbol.

i. Latitude:

Latitude is the angular distance of any point on Earth measured north or south of the equator in degrees, minutes and seconds.

The equator is a line going around Earth and is halfway between the North and South Poles, it is given a latitude of 0°. Values increasing north of the equa­tor and are considered positive and values decrease towards south of the equator and are sometimes con­sidered negative or have south attached to them.

For example, if a latitude of 30°N was given, this would mean that it was north of the equator. The latitude -30° or 30°S is a location south of the equator. On a map, these are the lines running horizontally from east-west.

Latitude lines are also sometimes called parallels because they are parallel and equidistant from each other. Each degree of latitude is about 69 miles (111 km) apart. The degree measure of latitude is the name of the angle from the equator.

While the parallel names the actual line along which degree points are measured. For example, 45 °N latitude is the angle of latitude between the equator and the 45th parallel (it is also halfway between the equator and the North Pole). The 45th parallel is the line along which all latitudinal values are 45°. The line is also parallel to the 46th and 44th parallels.

Like the equator, parallels are also considered circles of latitude or lines that circle the entire Earth. Since the equator divides the Earth into two equal halves and its centre coincides with that of the Earth, it is the only line of latitude that is a great circle while all other parallels are small circles.

Importance of Latitude:

Besides making it easier for one to locate different places on Earth, latitude is important to geography because it helps navigation and researchers understand the various patterns seen on Earth. High latitudes for example, have very different climates than low latitudes. In the Arctic it is much colder and drier than in the tropics. This is a direct result of the unequal distribution of solar insolation between the equator and the rest of the Earth.

Increasingly, latitude also results in extreme seasonal differences in climate because sunlight and sun angle vary at different times of the year depending on latitude. This affects temperature and the types of flora and fauna that can live in an area. Tropical rainforests for example, are the most biodiverse places in the world, while harsh conditions in the Arctic and Antarctic make it difficult for many species to survive.

Development of Latitudinal Measurements:

Since ancient times, people have tried to come up with reliable systems with which to measure their loca­tion on Earth. For centuries, both Greek and Chinese scientists attempted several different methods but a reliable one did not develop until the ancient Greek geographer, astronomer and mathematician, Ptolemy, created a grid system for the Earth. To do this, he divided a circle into 360°. Each degree comprised 60 minutes (60′) and each minute comprised 60 seconds (60″). He then applied this method to Earth’s surface and located places with degrees, minutes and seconds and published the coordinates in his book Geography.

Although this was the best attempt at defining the location of places on Earth at the time, the precise length of a degree of latitude was unresolved for around 17 centuries. In the middle ages, the system was finally fully developed and implemented with a degree being 69 miles (111 km) and with coordinates being written in degrees with the symbol Minutes and seconds are written with ‘, and “, respectively.

Important Lines of Latitude:

When studying latitude, there are three significant lines to remember. The first of these is the equator. The equator, located at 0°, is the longest line of latitude on Earth at 24,901.55 miles (40,075.16 km). It is significant because it is the exact centre of the Earth and it divides the Earth into the Northern and Southern Hemispheres. It also receives the direct sunlight on the two equinoxes.

At 23.5°N is the Tropic of Cancer. It runs through Mexico, Egypt, Saudi Arabia, India and Southern China. The Tropic of Capricorn is at 23.5°S and it runs through Chile, Southern Brazil, South Africa and Australia. These two parallels are significant because they receive direct sun on the two solstices. In addition, the area between the two lines is the area known as the tropics. This region does not experience seasons and the climate is normally warm and wet.

Finally, the Arctic Circle and Antarctic Circle are also important lines of latitude. They are at 66°32’N and 66°32’S. The climate of these locations is harsh and Antarctica is the largest desert in the world. These are also places that experience 24-hours sunlight and 24-hour darkness in the world.

Measuring Latitude:

Today, latitude is still measured in degrees, min­utes and seconds. A degree of latitude is still around 69 miles (111 km) while a minute is approximately 1.15 miles (1.85 km). A second of latitude is just over 100 feet (30 m). Paris, France for example, has a coordinate of 48°51’24″N. The 48° indicates that it lies near the 48th parallel while the minutes and seconds indicate just how close it is to that line. The N shows that it is north of the equator.

In addition to degrees, minutes and seconds, latitude can also be measured using decimal degrees. Paris’ location in this format looks like, 48.856°. Both formats are correct, although degrees, minutes and seconds is the most common format for latitude. Both however can be converted into the other and allow people to locate places on Earth within inches.

One nautical mile, a mile type used by sailors and navigators in the shipping and aviation indus­tries, represents one minute of latitude. Parallels of latitude are approximately 60 nautical (nm) apart.

Finally, areas described as having low latitude are those with lower coordinates or are closer to the equator while those with high latitudes have high coordinates and are far. For example, the Arctic Circle, which has a high latitude is at 66°32’N.

ii. Longitude:

Longitude is the angular distance of any point on Earth measured east or west of a point on Earth’s surface.

Unlike latitude there is no easy point of reference such as the equator to be designated as zero degrees in the longitude system. To avoid confusion, the world’s nations have agreed that the Prime Meridian, which passes through the Royal Observatory in Greenwich, England, will serve as that reference point and be designated as zero degrees.

Because of this designation, longitude is measured in degrees west or east of the Prime Meridian. For example, 30°E, the line passing through eastern Africa, is an angular distance of 30° east of the Prime Meridian. 30°W, which is in the middle of the Atlantic Ocean, is an angular distance of 30° west of the Prime Meridian.

There are 180 degrees east of the Prime Meridian and coordinates are sometimes given without the designation of ‘E’ or east. When this is used, a posi­tive value represents coordinates east of the Prime Meridian.

There are also 180 degrees west of the Prime Meridian and when ‘W’ or west is omitted in a coordinate a negative value such as -30° represents coordinates west of the Prime Meridian. The 180° line is neither east nor west and approximates the International Date Line.

On a map, lines of longitude are the vertical lines running from the North Pole to the South Pole and are perpendicular to the lines of latitude. Every line of longitude also crosses the equator. Because longitude lines are not parallel, they are known as meridians. Like parallels, meridians name the specific line and indicate the distance east or west of a 0° line. Meridians converge at the poles and are farthest apart at the equator [about 69 miles (111 km) apart].

Development and History of Longitude:

For centuries, mariners and explorers worked to determine their longitude in an effort to make navigation easier. Latitude was determined easily by observing the inclination of the sun or the position of known stars in the sky and calculating the angular distance from the horizon to them. Longitude could not be determined in this way because Earth’s rota­tion constantly changes the position of stars and the sun.

The first person to offer a method for measuring longitude was the explorer Amerigo Vespucci. In the late 1400s, he started measuring and comparing the positions of the moon and Mars with their predicted positions over several nights at the same time. In his measurements, Vespucci calculated the angle between his location, the moon and Mars.

By doing this, Vespucci got a rough estimate of longitude. This method did not become widely used, however because it relied on a specific astronomical event. Observers also needed to know the specific time and measure the moon and Mars’ positions on a stable viewing platform—both of which were difficult to do at sea.

In the early 1600s, a new idea to measure lon­gitude was developed when Galileo determined that it could be measured with two clocks. He said that any point on Earth took 24 hours to travel the full 360° rotation of Earth. He found that if you divide 360° by 24 hours, you find that a point on Earth travels 15° of longitude every hour.

Therefore, with an accurate clock at sea, a comparison of two clocks would determine longitude. One clock would be at the home port and the other on the ship. The clock on the ship would need to be reset to local noon each day. The time difference would then indicate the longitudinal difference travelled as one hour represented a 15° change in longitude.

Shortly thereafter, there were several attempts to make a clock that could accurately tell time on the unstable deck of a ship. In 1728, clockmaker John Harrison began working on the problem and in 1760, he produced the first marine chronometer called Number 4. In 1761, the chronometer was tested and determined to be accurate, officially making it possible to measure longitude on land and at sea.

Measuring Longitude:

Today, longitude is more accurately measured with atomic clocks and satellites. The Earth is still divided equally into 360° of longitude with 180° being east of the Prime Meridian and 180° west. Longitudinal coordinates are divided into degrees, minutes and seconds with 60 minutes making up a degree and 60 seconds comprising a minute.

For example, Beijing, China’s longitude is 116°23’30″E. The 116° indicates that it lies near the 116th meridian while the minutes and seconds indicate just how close it is to that line. The ‘E’ indicates that it is that distance east of the Prime Meridian. Although less common, longitude can also be written in decimal degrees.

In addition to the Prime Meridian, which is the 0° mark in today’s longitudinal system, the International Date Line is also an important marker. It is the 180° merid­ian on the opposite side of the Earth and is where the eastern and western hemispheres meet.

It also marks the place where each day officially begins. At the International Date Line, the west side of the line is always one day ahead of the east side, no matter what time of the day it is when the line is crossed. This is because the Earth rotates east on its axis.

Standard Time:

Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time, rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel.

The concept became established in the late 19th century. The time so set has come to be defined in terms of offsets from Universal time. Where daylight saving time is used as the term standard time typically refers to the time without the offset for daylight saving time.

The adoption of Standard Time, because of the inseparable correspondence between time and longitude, solidified the concepts of dividing the globe half into an eastern and western hemisphere, with one Prime Meridian (as well as its opposite International Date Line) replacing the various Prime Meridians that were in use.

International Date Line:

The International Date Line sits on the 180° line of longitude in the middle of the Pacific Ocean, and is the imaginary line that separates two consecutive calendar days. It is not a perfectly straight line and has been moved slightly over the years to accom­modate needs (or requests) of varied countries in the Pacific Ocean.

Note how it bends to include all of Kiribati, Samoa, Tonga and Tokelau in the Eastern Hemisphere. Immediately to the left of the Interna­tional Date Line the date is always one day ahead of the date (or day) immediately to the right of the International Date Line in the Western Hemisphere.

By Jesse Zanger

Updated on: April 6, 2024 / 11:47 AM EDT / CBS New York

NEW YORK - New York City and its surrounding area were hit by a significant earthquake and multiple aftershocks Friday.

A 3.8 magnitude aftershock hit 37 miles west of New York City near Gladstone, New Jersey, around 6 p.m. Friday. It struck 9.7 kilometers deep and was felt as far away as Long Island, where there were reports of houses shaking.

It was initially reported to be 4.0 magnitude, but was later confirmed to be 3.8. Seismologists said aftershocks could  continue for a week . 

New York Gov. Kathy Hochul said there were no immediate reports of significant damage after that aftershock, which came on the heels of Friday morning's 4.8 magnitude earthquake - one of the largest quakes to hit the region in a century. 

The quake hit at approximately 10:23 a.m., startling everyone. It struck 4.7 kilometers below the surface and  was centered in Readington Township, N.J. , about 40 miles west of New York City, according to the U.S. Geological Survey. 

Walls rattled and shelves shook throughout the area. Videos captured  various views of the moment the earthquake hit . 

The impact was felt throughout the Tri-State Area, as well as in  Philadelphia  and as far away as  Baltimore . The USGS said the impact was felt all the way from Maine to Washington, D.C.

There were multiple aftershocks after the earthquake hit. Before Friday evening's 3.8, there were several earlier in the day. An hour after the initial impact, a 2.0 aftershock struck west of Bedminster, N.J. At around 12:30 p.m., there was a 1.8 magnitude aftershock, another 2.0 aftershock at 1:14 p.m., and another 2.0 aftershock shortly before 3 p.m. 

"Aftershocks of these sizes are normal and are not expected to cause further damage," Hochul wrote on X. 

"One of the largest earthquakes on the East Coast in the last century" 

"We're taking this extremely seriously and here's why. There's always the possibility of aftershocks. We have not felt a magnitude of this earthquake since about 2011 ," Hochul said. "This is one of the largest earthquakes on the East Coast to occur in the last century." 

Hochul said she has started a damage assessment across the state , and spoke with New Jersey Gov. Phil Murphy, since the quake's epicenter was located in the Garden State. 

"It's been an unsettling day, to say the least," Hochul said. 

Murphy, who was at a conference out of state when the quake hit, touted the response locally . 

"The reaction was swift and very impressive by the likes of the Port Authority, our State Police opening up its emergency operations center, local and county officials," Murphy said. 

He said the top infrastructure concern is the Hudson River tunnels, though so far there were no reports of major damage. 

"The rail tunnels were built in, finished in 1911, which is why we're building two new ones," Murphy said. 

NYC Mayor Adams: "New Yorkers should go about their normal day"

New York City officials said there have been no reports of major impacts across the city. 

New York City Mayor Eric Adams said though there's always a concern about aftershocks , "New Yorkers should go about their normal day. First responders are working to make sure the city's safe." 

In the event of an aftershock, Adams said people should "drop to the floor, cover your head and neck, and take cover under a solid piece of furniture next to an interior wall, or in a doorway." 

Adams also said he's been in touch with the White House. 

"Earthquakes don't happen every day in New York, so this can be extremely traumatic - the number of texts, calls and inquiries that people sent out not only to our administration, but to family members. Check in on them. We know how this can impact you," Adams said. 

"We activated our protocols for this earthquake. We immediately started coordinating with all city, state, federal and our utility partners. Public notifications were sent out both by Notify NYC and our wireless emergency alert system," New York City Emergency Management Commissioner Zachary Iscol said. 

"We are putting on additional construction and engineering professionals from this point on over the weekend, so if reports do come in, we will be ready to respond," Department of Buildings Commissioner James Oddo said. 

City officials say if people sees cracks in their home or business as a result of the earthquake , they should call 311. 

New York City public schools were told to continue operations and hold dismissal as normal.

"Parents do not need to pick up their child early as a result of today's earthquake. Additionally, all after-school programs will continue as planned," New York City Schools Chancellor David Banks said. " All of our students across the school system are safe . All of our staff are safe. We have no reports of any structural damage to any of our school facilities, while many schools in fact felt some tremors from the earthquake." 

Adams said he was at a Youth Gun Summit at Gracie Mansion and did not feel the quake himself. 

"I would encourage all New Yorkers to use this as a wakeup call to make sure that they are prepared for future seismic activity. Know what to do - know not to evacuate outside your building. Know if you are outside to stay away from power lines or things that can collapse. Make sure you have emergency supplies on hand. Make sure you have a plan for your family," Iscol said. 

Traffic, transit and airport impacts of the quake

The quake caused temporary ground stops at John F. Kennedy and Newark Liberty airports. There were delays as well at LaGuardia as crews checked for damage to the airports and runways

The MTA said it is inspecting all New York City-area bridges and tunnels . Officials also said subway tunnels were checked. 

"Initial inspections show there was not damage to any MTA infrastructure, but we will continue to monitor the situation closely," the MTA posted on X. 

Amtrak and MTA service remained on their full schedule, Hochul said. 

New Yorkers, area residents shaken up by unusual earthquake

The experience was more than enough to rattle some New Yorkers . 

"I was laying in my bed, and my whole apartment building started shaking. I started freaking out," one New York City resident told CBS New York's Elijah Westbrook. 

"My class was scared. So my friends, they went next to me and gave me a hug," 6-year-old Trinity Morales told CBS New York's Jennifer Bisram. 

"I was sound asleep. I got home late last night, had a little bit of water in the basement, so I was up until like 4:30. I was sound asleep at 10:23. This thing rattled me up," CBS New York's Lonnie Quinn said. "I initially thought it was wind, because my windows were rattling and shaking. Looked outside, the trees were not blowing. I thought, what is that?" 

Cracks in walls were visible in an apartment in Berkeley Heights, N.J. 

The Empire State Building had bit of fun after the quake . 

"I AM FINE," the building posted on X. 

More history of earthquakes in New York

It's not the first time the East Coast and New York City have been hit with a quake. A 5.0 quake was measured in New York City in 1884. 

By way of comparison, a 4.0 earthquake is the equivalent of 33,000 pounds of explosive going off at any one time. A 5.0 earthquake is the equivalent of a million pounds of explosives. The record for New Jersey is a 5.3.   

There's a major fault line in New Jersey called the Ramapo Fault, which stems from the Appalachian mountains, and there are at least five smaller fault lines under Manhattan island. 

The quake comes just a few months after the USGS warned nearly 75% of the United States could face damaging quakes in the next 100 years . 

In 2011, a 5.8 quake struck in Virginia and rattled the entire East Coast .   

Jesse Zanger is the managing editor of CBSNewYork.com.

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Why Taiwan Was So Prepared for a Powerful Earthquake

Decades of learning from disasters, tightening building codes and increasing public awareness may have helped its people better weather strong quakes.

Search-and-rescue teams recover a body from a leaning building in Hualien, Taiwan. Thanks to improvements in building codes after past earthquakes, many structures withstood Wednesday’s quake. Credit...

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By Chris Buckley ,  Meaghan Tobin and Siyi Zhao

Photographs by Lam Yik Fei

Chris Buckley reported from the city of Hualien, Meaghan Tobin from Taipei, in Taiwan.

• April 4, 2024

When the largest earthquake in Taiwan in half a century struck off its east coast, the buildings in the closest city, Hualien, swayed and rocked. As more than 300 aftershocks rocked the island over the next 24 hours to Thursday morning, the buildings shook again and again.

But for the most part, they stood.

Even the two buildings that suffered the most damage remained largely intact, allowing residents to climb to safety out the windows of upper stories. One of them, the rounded, red brick Uranus Building, which leaned precariously after its first floors collapsed, was mostly drawing curious onlookers.

The building is a reminder of how much Taiwan has prepared for disasters like the magnitude-7.4 earthquake that jolted the island on Wednesday. Perhaps because of improvements in building codes, greater public awareness and highly trained search-and-rescue operations — and, likely, a dose of good luck — the casualty figures were relatively low. By Thursday, 10 people had died and more than 1,000 others were injured. Several dozen were missing.

“Similar level earthquakes in other societies have killed far more people,” said Daniel Aldrich , a director of the Global Resilience Institute at Northeastern University. Of Taiwan, he added: “And most of these deaths, it seems, have come from rock slides and boulders, rather than building collapses.”

Across the island, rail traffic had resumed by Thursday, including trains to Hualien. Workers who had been stuck in a rock quarry were lifted out by helicopter. Roads were slowly being repaired. Hundreds of people were stranded at a hotel near a national park because of a blocked road, but they were visited by rescuers and medics.

On Thursday in Hualien city, the area around the Uranus Building was sealed off, while construction workers tried to prevent the leaning structure from toppling completely. First they placed three-legged concrete blocks that resembled giant Lego pieces in front of the building, and then they piled dirt and rocks on top of those blocks with excavators.

“We came to see for ourselves how serious it was, why it has tilted,” said Chang Mei-chu, 66, a retiree who rode a scooter with her husband Lai Yung-chi, 72, to the building on Thursday. Mr. Lai said he was a retired builder who used to install power and water pipes in buildings, and so he knew about building standards. The couple’s apartment, near Hualien’s train station, had not been badly damaged, he said.

“I wasn’t worried about our building, because I know they paid attention to earthquake resistance when building it. I watched them pour the cement to make sure,” Mr. Lai said. “There have been improvements. After each earthquake, they raise the standards some more.”

It was possible to walk for city blocks without seeing clear signs of the powerful earthquake. Many buildings remained intact, some of them old and weather-worn; others modern, multistory concrete-and-glass structures. Shops were open, selling coffee, ice cream and betel nuts. Next to the Uranus Building, a popular night market with food stalls offering fried seafood, dumplings and sweets was up and running by Thursday evening.

Earthquakes are unavoidable in Taiwan, which sits on multiple active faults. Decades of work learning from other disasters, implementing strict building codes and increasing public awareness have gone into helping its people weather frequent strong quakes.

Not far from the Uranus Building, for example, officials had inspected a building with cracked pillars and concluded that it was dangerous to stay in. Residents were given 15 minutes to dash inside and retrieve as many belongings as they could. Some ran out with computers, while others threw bags of clothes out of windows onto the street, which was also still littered with broken glass and cement fragments from the quake.

One of its residents, Chen Ching-ming, a preacher at a church next door, said he thought the building might be torn down. He was able to salvage a TV and some bedding, which now sat on the sidewalk, and was preparing to go back in for more. “I’ll lose a lot of valuable things — a fridge, a microwave, a washing machine,” he said. “All gone.”

Requirements for earthquake resistance have been built into Taiwan’s building codes since 1974. In the decades since, the writers of Taiwan’s building code also applied lessons learned from other major earthquakes around the world, including in Mexico and Los Angeles, to strengthen Taiwan’s code.

After more than 2,400 people were killed and at least 10,000 others injured during the Chi-Chi quake of 1999, thousands of buildings built before the quake were reviewed and reinforced. After another strong quake in 2018 in Hualien, the government ordered a new round of building inspections. Since then, multiple updates to the building code have been released.

“We have retrofitted more than 10,000 school buildings in the last 20 years,” said Chung-Che Chou, the director general of the National Center for Research on Earthquake Engineering in Taipei.

The government had also helped reinforce private apartment buildings over the past six years by adding new steel braces and increasing column and beam sizes, Dr. Chou said. Not far from the buildings that partially collapsed in Hualien, some of the older buildings that had been retrofitted in this way survived Wednesday’s quake, he said.

The result of all this is that even Taiwan’s tallest skyscrapers can withstand regular seismic jolts. The capital city’s most iconic building, Taipei 101, once the tallest building in the world, was engineered to stand through typhoon winds and frequent quakes. Still, some experts say that more needs to be done to either strengthen or demolish structures that don’t meet standards, and such calls have grown louder in the wake of the latest earthquake.

Taiwan has another major reason to protect its infrastructure: It is home to the majority of production for the Taiwan Semiconductor Manufacturing Company, the world’s largest maker of advanced computer chips. The supply chain for electronics from smartphones to cars to fighter jets rests on the output of TSMC’s factories, which make these chips in facilities that cost billions of dollars to build.

The 1999 quake also prompted TSMC to take extra steps to insulate its factories from earthquake damage. The company made major structural adjustments and adopted new technologies like early warning systems. When another large quake struck the southern city of Kaohsiung in February 2016, TSMC’s two nearby factories survived without structural damage.

Taiwan has made strides in its response to disasters, experts say. In the first 24 hours after the quake, rescuers freed hundreds of people who were trapped in cars in between rockfalls on the highway and stranded on mountain ledges in rock quarries.

“After years of hard work on capacity building, the overall performance of the island has improved significantly,” said Bruce Wong, an emergency management consultant in Hong Kong. Taiwan’s rescue teams have come to specialize in complex efforts, he said, and it has also been able to tap the skills of trained volunteers.

Taiwan’s resilience also stems from a strong civil society that is involved in public preparedness for disasters.

Ou Chi-hu, a member of a group of Taiwanese military veterans, was helping distribute water and other supplies at a school that was serving as a shelter for displaced residents in Hualien. He said that people had learned from the 1999 earthquake how to be more prepared.

“They know to shelter in a corner of the room or somewhere else safer,” he said. Many residents also keep a bag of essentials next to their beds, and own fire extinguishers, he added.

Around him, a dozen or so other charities and groups were offering residents food, money, counseling and childcare. The Tzu Chi Foundation, a large Taiwanese Buddhist charity, provided tents for families to use inside the school hall so they could have more privacy. Huang Yu-chi, a disaster relief manager with the foundation, said nonprofits had learned from earlier disasters.

“Now we’re more systematic and have a better idea of disaster prevention,” Mr. Huang said.

Mike Ives contributed reporting from Seoul.

Chris Buckley , the chief China correspondent for The Times, reports on China and Taiwan from Taipei, focused on politics, social change and security and military issues. More about Chris Buckley

Meaghan Tobin is a technology correspondent for The Times based in Taipei, covering business and tech stories in Asia with a focus on China. More about Meaghan Tobin

Siyi Zhao is a reporter and researcher who covers news in mainland China for The Times in Seoul. More about Siyi Zhao

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