essay about the unique characteristics and properties of the earth

5 Unique Characteristics of Earth

Earth has many characteristics that make it unique among all the other planets in the Solar system. For starters, ours is the only planet that can support life (as far as we know). But what is it that makes the planet have these special conditions that none of the other planets have?

Earth is not particularly big, it doesn’t have materials that other planets don’t, and its formation process was very similar to the rest. So it must be something else.

In this article, we’ll take a look at some of the unique characteristics of Earth and what they have meant for the development of life and the ecosystem that we have on our planet.

All of the comparisons are going to be made against the other planets in the Solar system. We don’t have enough information about exoplanets in other star systems to make definitive statements. Astronomers believe there are many planets that have similar characteristics to Earth in the universe but we don’t have enough data about them yet to compare them.

Earth Characteristics

1) earth has liquid water on its surface.

Earth is the only planet in the Solar system that is located in the habitable zone.

The habitable zone (also called the goldilocks zone ) is the area around a star where a planet could support liquid water. The distance varies from star to star and depends on its size and type.

The Sun’s habitable zone is somewhere between 0.9 and 1.2 Astronomical Units (134 million kilometers to 179 million kilometers). Earth is the only planet that is fully located within this range. Mars is right on the edge of it and that’s part of the reason why some scientists believe the red planet could have had water oceans in the past.

Some Moons and planets in the Solar system are theorized to have liquid water. Such is the case of Neptune, Uranus, Triton, Titan, Europa, and others. But in those cases, the water would be contained within temperature pockets beneath the surface or in a mantle close to their core.

Approximately 71% of Earth’s surface is covered in water. All of that makes up about 96% of all the water on the planet. The rest is divided between air vapor, ice caps, glaciers, and moisture in the soil.

2) Earth is the only planet with continents

Continents are large, continuous masses of land that sit on top of plate tectonics and “float” on the planet’s mantle. As plate tectonics move and geological activity happen in the form of volcanoes, for example, contents drift and re-adjust. That’s how we went from a single one to the seven that we know today.

But Earth is the only planet in the Solar system that has continents. And that is because it is also the only one of the inner (rocky) planets to have plate tectonics. Without them, the geological activity that is necessary to form these huge land masses just doesn’t happen.

Instead, the surface of the other rocky planets (Mercury, Venus, and Mars) is more uniform even though they do have some mountains and other features that resulted from geological activity in the past. In the case of Venus, it might even have active volcanoes today but we don’t know for sure.

As for the rest of the planets (Jupiter, Saturn, Uranus, and Neptune), since they are made out of gas and don’t have a surface, it is not possible for them to have continents.

While on Earth continents are divided by oceans, it is debated whether oceans of liquid water are necessary for continents to form.

3) Earth is the only planet with just one Moon

The following table lists the number of moons (satellites) each planet in the Solar system has.

As you can see, planets in the Solar system have either zero satellites or more than one, with Earth being the only exception.

This is because of a combination of factors.

First, the planets that are closer to their stars can’t capture moons because the gravitational pull is too strong and takes them out of their orbits.

Gas giants like Jupiter and Saturn tend to capture many moons because of their large mass. In fact, we are still discovering new moons for these planets. It is possible they have more that have yet to be found. Most of these moons are quite small, but there are some like Ganymede in Jupiter that is even bigger than ours.

So, the reasons why our planet has only one moon are a combination of its mass, distance from the Sun, etc.

But this might have not always been the case. Some scientists believe Earth might have had two moons in the past and they could have collided to form the single one that we know today.

4) Earth’s atmosphere is very different from the other planets’

The atmosphere is an outer layer of gas that planets have that is located between the planet and space. On Earth and other rocky planets, the atmosphere sits on top of the surface and it is what contains the air we breathe.

One of the characteristics that make Earth so unique when compared to the other planets is the composition of its atmosphere. Most planet’s atmosphere is mostly made up of hydrogen or carbon dioxide. But Earth is the only planet with an atmosphere that is primarily made up of nitrogen.

This is the reason why we wouldn’t be able to breathe on Mars .

The following table shows the percentage of the elements contained in each of the planet’s atmospheres.

As you can see, Earth’s atmospheric composition is very different from the rest.

At this point, you might be wondering why is it that if we need oxygen to breathe, most of the air we breathe is actually nitrogen? Well, it turns out nitrogen is an inert gas. This means it does not take part in any biochemical reactions in our bodies. We do not consume it like oxygen, and we do not produce it like carbon dioxide. We simply breathe it in and breathe it out.

This difference in composition between Earth’s atmosphere and the other planets is one of the greatest challenges that we’ll face when we try to live on other planets. For example, to survive on Mars , we’ll have to figure out a reliable way to extract oxygen.

5) Earth’s temperature is stable

Planets change significantly throughout their lifespan. There was a time when Earth’s surface was as hot as 3,680°F (2026°C) when the Moon was being formed out of an impact with another object, possibly a planet.

But while other planets have seen extreme changes in their temperatures, Earth’s has remained more or less stable for most of its lifespan. It is believed that both Venus and Mars had the necessary temperature conditions to support liquid water on their surfaces too, but the changes they went through turned them into what we know today. For Venus, it was an extreme greenhouse effect that raised its temperature, while on Mars, it was probably due to a thin, leaky atmosphere.

Earth, on the other hand, has had a relatively stable temperature for the last 4 billion years. Coincidentally, that’s around the same time when life began. Scientists believe the first microorganisms started to live on the planet approximately 3.7 billion years ago.

This stability in temperature is thanks to a natural cycle that acts similar to a thermostat and “adjusts” the planet’s temperature. I’m going to heavily oversimplify it, but it works kind of like this:

• Volcanoes spew CO2 (carbon dioxide) into the atmosphere.
• The CO2 raises the temperature of the planet, causing water to evaporate
• This created clouds, which in turn, results in acid rain (because of the CO2)
• This acidic rain dissolves minerals from the rocks
• Minerals wash into rivers and oceans and eventually precipitate to form new rocks that contain carbon
• Plate tectonics and geological activity move these rocks into the mantle
• CO2 is “baked” out of these rocks due to the heat
• CO2 is expelled again when volcanoes erupt

As you can see, this cycle is slightly self-adjusting. The more CO2 there is in the atmosphere, the more water is evaporated, which leads to more rain, and so on.

However, the cycle is not infinite. There is a tipping point at which there can be too much CO2 and that’s what caused the greenhouse effect that turned Venus into the inhabitable big ball of heat that it is today. And this is why scientists worry so much about excess CO2 in the atmosphere.

• Earth’s unique characteristics are what has allowed it to support life
• These characteristics include its stable temperature, a dense nitrogen-based atmosphere, and its position in the Solar system, among others.
• Drastic changes to these variables could affect the ability of the planet to support liquid water, and therefore, its ability to sustain life.

Elena is a Canadian journalist and researcher. She has been looking at the sky for years and hopes to introduce more people to the wonderful hobby that is astronomy.

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• What Makes Earth A Unique Planet In The Solar System?

In the solar system, the Earth is the third planet from the sun, and it is the only planet known to have life. According to different sources of evidence like radiometric dating, the Earth is believed to be more than 4.5 billion years old. Out of the four terrestrial planets , the Earth is the largest and densest planet. The lithosphere is made up of numerous tectonic plates that keep moving over millions of years. Water in the oceans cover about 71% of the total surface of the Earth, and the remaining 29% is covered by the continents and islands, which have rivers and lakes. The ability of the Earth to harbor life makes the Earth a unique planet in the solar system, and this stems from the fact that water in liquid form exists on the planet. Similarly, the existence of gaseous oxygen in the atmosphere of the Earth also supports life.

Evolution Of Life On Earth

It is believed that about 4 billion years ago, a chemical reaction was triggered which led to the first self-replicating molecules. Later, about half a billion years ago, the last common ancestor of all the present life forms arose. Photosynthesis evolved to allow the energy of the sun to be harvested, and the resulting oxygen accumulated in the atmosphere. The interaction between the oxygen and ultraviolet radiation from the sun led to the formation of the ozone layer, which is a protective layer in the atmosphere. The most important step was when the smaller cells were incorporated within larger cells leading to the development of larger and complex cells of eukaryotes. Multicellular organisms were formed when colonies of cells became more specialized. 

Tectonic Plates

According to some planetary geologists, the Martian surfaces have certain features that could indicate the planet may have had some active volcanoes in the past, particularly during its early phases when it was formed. Other than this possibility, which remains to be confirmed, no other planet in the solar system other than the Earth has tectonic plates. In this regard, the Earth is unique among the planets in the solar system due to the tectonic plates which are constantly moving because they are being driven by the convective loops of hot rock in the core. The lithosphere on our planet is divided into different tectonic plates, which move relative to each other at one of the three types of boundaries. At a convergent boundary, the plates shift towards each other, at divergent boundaries the plates move in the opposite direction away from each other, and at the transform boundary, the plates shift laterally past each other. A lot of activity occurs along these tectonic plate boundaries and they are associated with the formation of oceanic trenches , mountains, volcanic activity, and earthquakes. Currently, there are seven main tectonic plates, and they include the Pacific, South American, African, Indo-Australian, Antarctic, North American, and Eurasian. Other smaller plates include Scotia Plate located in South Atlantic Ocean, Nazca Plate which is found in the west coast of South America, the Caribbean Plate, and the Arabian Plate.

Origin Of Oxygen On Earth

The Earth is the only planet in our solar system that has oxygen in gaseous form. In its formative years, the Earth had an oxygen-free atmosphere, and it took several millions of years before oxygen was sufficient to keep organisms alive on our planet. Initially, the Earth's atmosphere was made up of nitrogen, methane, and carbon dioxide. The rays from the sun were able to split carbon dioxide to free some oxygen and other molecules. During this early period, the oxygen created would disappear as soon as it was formed because of the ability of oxygen to form bonds quickly with other molecules. For instance, it would bond with hydrogen from volcanoes to form hydrogen peroxide among other compounds. About 3 billion years ago, the Earth's atmosphere had about 0.03% of the current oxygen levels in the atmosphere. At this time, some microbes had evolved and were able to carry out photosynthesis and generate oxygen.

The Earth's Biosphere

Different life forms on Earth inhabit different ecosystems and all ecosystems form the biosphere. The biosphere on Earth is divided into different biomes, and it is believed to have evolved over billions of years. On land, biomes are typically separated by humidity, height above sea level, and latitudes. Broadly similar animals and plants inhabit the same biome. A biosphere can be referred to as a zone of life on the planet Earth, and it is almost self-regulating.

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Planet Earth, explained

Our home planet provides us with life and protects us from space.

Earth, our home planet, is a world unlike any other. The third planet from the sun, Earth is the only place in the known universe confirmed to host life.

With a radius of 3,959 miles, Earth is the fifth largest planet in our solar system, and it's the only one known for sure to have liquid water on its surface. Earth is also unique in terms of monikers. Every other solar system planet was named for a Greek or Roman deity, but for at least a thousand years, some cultures have described our world using the Germanic word “earth,” which means simply “the ground.”

Our dance around the sun

Earth orbits the sun once every 365.25 days. Since our calendar years have only 365 days, we add an extra leap day every four years to account for the difference.

Though we can't feel it, Earth zooms through its orbit at an average velocity of 18.5 miles a second. During this circuit, our planet is an average of 93 million miles away from the sun, a distance that takes light about eight minutes to traverse. Astronomers define this distance as one astronomical unit (AU), a measure that serves as a handy cosmic yardstick.

Earth rotates on its axis every 23.9 hours, defining day and night for surface dwellers. This axis of rotation is tilted 23.4 degrees away from the plane of Earth's orbit around the sun, giving us seasons. Whichever hemisphere is tilted closer to the sun experiences summer, while the hemisphere tilted away gets winter. In the spring and fall, each hemisphere receives similar amounts of light. On two specific dates each year—called the equinoxes—both hemispheres get illuminated equally.

Many layers, many features

About 4.5 billion years ago, gravity coaxed Earth to form from the gaseous, dusty disk that surrounded our young sun. Over time, Earth's interior—which is made mostly of silicate rocks and metals—differentiated into four layers.

At the planet's heart lies the inner core, a solid sphere of iron and nickel that's 759 miles wide and as hot as 9,800 degrees Fahrenheit. The inner core is surrounded by the outer core, a 1,400-mile-thick band of iron and nickel fluids. Beyond the outer core lies the mantle, a 1,800-mile-thick layer of viscous molten rock on which Earth's outermost layer, the crust, rests. On land, the continental crust is an average of 19 miles thick, but the oceanic crust that forms the seafloor is thinner—about three miles thick—and denser.

Like Venus and Mars, Earth has mountains, valleys, and volcanoes. But unlike its rocky siblings, almost 70 percent of Earth's surface is covered in oceans of liquid water that average 2.5 miles deep. These bodies of water contain 97 percent of Earth's volcanoes and the mid-ocean ridge , a massive mountain range more than 40,000 miles long.

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Earth's crust and upper mantle are divided into massive plates that grind against each other in slow motion. As these plates collide, tear apart, or slide past each other, they give rise to our very active geology. Earthquakes rumble as these plates snag and slip past each other. Many volcanoes form as seafloor crust smashes into and slides beneath continental crust. When plates of continental crust collide, mountain ranges such as the Himalaya are pushed toward the skies.

Protective fields and gases

Earth's atmosphere is 78 percent nitrogen, 21 percent oxygen, and one percent other gases such as carbon dioxide, water vapor, and argon. Much like a greenhouse, this blanket of gases absorbs and retains heat. On average, Earth's surface temperature is about 57 degrees Fahrenheit; without our atmosphere, it'd be zero degrees . In the last two centuries, humans have added enough greenhouse gases to the atmosphere to raise Earth's average temperature by 1.8 degrees Fahrenheit . This extra heat has altered Earth's weather patterns in many ways .

The atmosphere not only nourishes life on Earth, but it also protects it: It's thick enough that many meteorites burn up before impact from friction, and its gases—such as ozone—block DNA-damaging ultraviolet light from reaching the surface. But for all that our atmosphere does, it's surprisingly thin. Ninety percent of Earth's atmosphere lies within just 10 miles of the planet's surface .

The silhouette of a woman is seen on a Norwegian island beneath the Northern Lights ( aurora borealis ).

We also enjoy protection from Earth's magnetic field, generated by our planet's rotation and its iron-nickel core. This teardrop-shaped field shields Earth from high-energy particles launched at us from the sun and elsewhere in the cosmos. But due to the field's structure, some particles get funneled to Earth's Poles and collide with our atmosphere, yielding aurorae, the natural fireworks show known by some as the northern lights.

Spaceship Earth

Earth is the planet we have the best opportunity to understand in detail—helping us see how other rocky planets behave, even those orbiting distant stars. As a result, scientists are increasingly monitoring Earth from space. NASA alone has dozens of missions dedicated to solving our planet's mysteries.

At the same time, telescopes are gazing outward to find other Earths. Thanks to instruments such as NASA's Kepler Space Telescope, astronomers have found more than 3,800 planets orbiting other stars, some of which are about the size of Earth , and a handful of which orbit in the zones around their stars that are just the right temperature to be potentially habitable. Other missions, such as the Transiting Exoplanet Survey Satellite, are poised to find even more.

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ENCYCLOPEDIC ENTRY

Earth is the planet we live on, the third of eight planets in our solar system and the only known place in the universe to support life.

Earth Science, Astronomy, Geology, Geography, Physical Geography

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Learning materials.

• The active outer shell of Earth is dominated by tectonic plates, whose interactions result in volcanic eruptions, earthquakes, and geysers. Click to visit MapMaker Interactive's layer on Earth's tectonic plates.

Earth is the planet we live on, one of eight planets in our solar system and the only known place in the universe to support life.

Earth is the third planet from the sun , after Mercury and Venus, and before Mars. It is about 150 million kilometers (about 93 million miles) from the sun. This distance, called an astronomical unit (AU), is a standard unit of measurement in astronomy . Earth is one AU from the sun. The planet Jupiter is about 5.2 AU from the sun—about 778 million kilometers (483.5 million miles).

Earth is the largest and most massive of the rocky inner planets , although it is dwarfed by the gas giants beyond the Asteroid Belt . Its diameter is about 12,700 kilometers (7,900 miles), and its mass is about 5.97×1024 kilograms (6.58×1021 tons). In contrast, Jupiter, the largest planet in the solar system, has a diameter of 143,000 kilometers (88,850 miles), and its mass is about 1,898×1024 kilograms (2093×1021 tons).

Earth is an oblate spheroid . This means it is spherical in shape, but not perfectly round. It has a slightly greater radius at the Equator , the imaginary line running horizontally around the middle of the planet. In addition to bulging in the middle, Earth’s poles are slightly flattened. The geoid describes the model shape of Earth, and is used to calculate precise surface locations.

Earth has one natural satellite , the moon . Earth is the only planet in the solar system to have one moon. Venus and Mercury do not have any moons, for example, while Jupiter and Saturn each have more than a dozen.

Planet Earth  

Earth’s interior is a complex structure of superheated rocks. Most geologists recognize three major layers: the dense core , the bulky mantle , and the brittle crust . No one has ever ventured below Earth’s crust.

Earth’s core is mostly made of iron and nickel . It consists of a solid center surrounded by an outer layer of liquid . The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles).

A mantle of heavy rock (mostly silicates ) surrounds the core. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84 percent of Earth’s total volume . Parts of the mantle are molten , meaning they are composed of partly melted rock. The mantle’s molten rock is constantly in motion. It is forced to the surface during volcanic eruptions and at mid-ocean ridges .

Earth’s crust is the planet’s thinnest layer, accounting for just one percent of Earth’s mass. There are two kinds of crust: thin, dense oceanic crust and thick, less-dense continental crust . Oceanic crust extends about five to 10 kilometers (three to six miles) beneath the ocean floor. Continental crust is about 35 to 70 kilometers (22 to 44 miles) thick.

Exterior: Tectonic Activity

The crust is covered by a series of constantly moving tectonic plates . New crust is created along mid-ocean ridges and rift valleys , where plates pull apart from each other in a process called rifting . Plates slide above and below each other in a process called subduction . They crash against each other in a process called faulting .

Tectonic activity such as subduction and faulting has shaped the crust into a variety of landscapes . Earth’s highest point is Mount Everest, Nepal, which soars 8,850 kilometers (29,035 feet) in the Himalaya Mountains in Asia. Mount Everest continues to grow every year, as subduction drives the Indo-Australian tectonic plate below the Eurasian tectonic plate. Subduction also creates Earth’s deepest point, the Mariana Trench, about 11 kilometers (6.9 miles) below the surface of the Pacific Ocean. The heavy Pacific plate is being subducted beneath the small Mariana plate.

Plate tectonics are also responsible for landforms such as geysers , earthquakes , and volcanoes . Tectonic activity around the Pacific plate, for instance, creates the Ring of Fire . This tectonically active area includes volcanoes such as Mount Fuji, Japan, and earthquake-prone fault zones such as the west coast of the United States.

Revolution and Rotation

Earth is a rocky body constantly moving around the sun in a path called an orbit . Earth and the moon follow a slightly oval-shaped orbit around the sun every year.

Each journey around the sun, a trip of about 940 million kilometers (584 million miles), is called a revolution. A year on Earth is the time it takes to complete one revolution, about 365.25 days. Earth orbits the sun at a speedy rate of about 30 kilometers per second (18.5 miles per second).

At the same time that it revolves around the sun, Earth rotates on its own axis . Rotation is when an object, such as a planet, turns around an invisible line running down its center. Earth’s axis is vertical, running from the North Pole to the South Pole. Earth makes one complete rotation about every 24 hours. Earth rotates unevenly, spinning faster at the Equator than at the poles. At the Equator, Earth rotates at about 1,670 kilometers per hour (1,040 miles per hour), while at 45° north, for example, (the approximate latitude of Green Bay, Wisconsin, United States) Earth rotates at 1,180 kilometers per hour (733 miles per hour).

Earth’s rotation causes the periods of light and darkness we call day and night. The part of Earth facing the sun is in daylight; the part facing away from the sun is in darkness. If Earth did not rotate, one-half of Earth would always be too hot to support life, and the other half would be frozen. Earth rotates from west to east, so the sun appears to rise in the east and set in the west. 

In addition to Earth’s revolution and rotation periods, we experience light and darkness due to Earth’s axis not being straight up-and-down. Earth’s axis of rotation is tilted 23.5°. This tilt influences temperature changes and other weather patterns from season to season. 

The Spheres

Earth’s physical environment is often described in terms of spheres: the magnetosphere , the atmosphere , the hydrosphere , and the lithosphere . Parts of these spheres make up the biosphere , the area of Earth where life exists.

Magnetosphere

Earth’s magnetosphere describes the pocket of space surrounding our planet where charged particles are controlled by Earth’s magnetic field .

The charged particles that int eract with Earth’s magnetosphere are called the solar wind . The pressure of the solar wind compresses the magnetosphere on the “dayside” of Earth to about 10 Earth radii. The long tail of the magnetosphere on the “nightside” of Earth stretches to hundreds of Earth radii. The most well-known aspect of the magnetosphere are the charged particles that sometimes interact over its poles—the auroras , or Northern and Southern Lights.

Earth’s atmosphere is a blanket of gases enveloping Earth and retained by our planet’s gravity . Atmospheric gases include nitrogen, water vapor , oxygen , and carbon dioxide .

The atmosphere is responsible for temperature and other weather patterns on Earth. It blocks most of the sun’s ultraviolet radiation (UV), conducts solar radiation and precipitation through constantly moving air masses , and keeps our planet’s average surface temperature to about 15° Celsius (59° Fahrenheit).

The atmosphere has a layered structure. From the ground toward the sky, the layers are the troposphere , stratosphere , mesosphere , thermosphere , and exosphere . Up to 75 percent of the total mass of the atmosphere is in the troposphere, where most weather occurs. The boundaries between the layers are not clearly defined, and change depending on latitude and season.

Hydrosphere

The hydrosphere is composed of all the water on Earth. Nearly three-fourths of Earth is covered in water, most of it in the ocean. Less than three percent of the hydrosphere is made up of freshwater . Most freshwater is frozen in ice sheets and glaciers in Antarctica, the North American island of Greenland, and the Arctic. Freshwater can also be found underground, in chambers called aquifers , as well as rivers , lakes , and springs .

Water also circulates around the world as vapor. Water vapor can condense into clouds and fall back to Earth as precipitation.

The hydrosphere helps regulate Earth’s temperature and climate . The ocean absorbs heat from the sun and interacts with the atmosphere to move it around Earth in air currents .

Lithosphere

The lithosphere is Earth’s solid shell. The crust and the upper portion of the mantle form the lithosphere. It extends from Earth’s surface to between 50 and 280 kilometers (31 to 174 miles) below it. The difference in thickness accounts for both thin oceanic and thicker continental crust.

The rocks and minerals in Earth’s lithosphere are made of many elements . Rocks with oxygen and silicon , the most abundant elements in the lithosphere, are called silicates. Quartz is the most common silicate in the lithosphere—and the most common type of rock on Earth.

Cycles on Earth

Almost all materials on Earth are constantly being recycled . The three most common cycles are the water cycle , the carbon cycle , and the rock cycle .

Water Cycle

The water cycle involves three main phases, related to the three states of water: solid, liquid, and gas. Ice , or solid water, is most common near the poles and at high altitudes . Ice sheets and glaciers hold the most solid water.

Ice sheets and glaciers melt, transforming into liquid water. The most abundant liquid water on the planet is in the ocean, although lakes, rivers, and underground aquifers also hold liquid water. Life on Earth is dependent on a supply of liquid water. Most organisms, in fact, are made up mostly of liquid water, called body water . The human body is about 50 percent to 60 percent body water. In addition to survival and hygiene , people use liquid water for energy and transportation .

The third phase of the water cycle occurs as liquid water evaporates. Evaporation is the process of a liquid turning into a gas, or vapor. Water vapor is invisible and makes up part of the atmosphere. As water vapor condenses, or turns back into liquid, pockets of vapor become visible as clouds and fog . Eventually, clouds and fog become saturated , or full of liquid water. This liquid water falls to Earth as precipitation. It can then enter a body of water, such as an ocean or lake, or freeze and become part of a glacier or ice sheet. The water cycle starts again.

Carbon Cycle

The carbon cycle involves the exchange of the element carbon through Earth’s atmosphere, hydrosphere, and lithosphere. Carbon, essential for all life on Earth, enters the biosphere many ways. Carbon is one of the gases that make up the atmosphere. It is also ejected during the eruption of volcanoes and ocean vents .

All living or once-living materials contain carbon. These materials are organic . Plants and other autotrophs depend on carbon dioxide to create nutrients in a process called photosynthesis . These nutrients contain carbon. Animals and other organisms that consume autotrophs obtain carbon. Fossil fuels , the remains of ancient plants and animals, contain very high amounts of carbon.

As organisms die and decompose , they release carbon into the ocean, soil , or atmosphere. Plants and other autotrophs use this carbon for photosynthesis, starting the carbon cycle again.

The rock cycle is a process that explains the relationship between the three main types of rocks: igneous, sedimentary, and metamorphic. Unlike water in the water cycle and or carbon in the carbon cycle, not all rocks are recycled in different forms. There are some rocks that have been in their present form since soon after Earth cooled. These stable rock formations are called cratons .

Igneous rocks are formed as lava hardens. Lava is molten rock ejected by volcanoes during eruptions. Granite and basalt are common types of igneous rocks. Igneous rocks can be broken apart by the forces of erosion and weathering . Winds or ocean currents may then transport these tiny rocks ( sand and dust ) to a different location.

Sedimentary rocks are created from millions of tiny particles slowly building up over time. Igneous rocks can become sedimentary by collecting with other rocks into layers. Sedimentary rocks include sandstone and limestone .

Metamorphic rocks are formed when rocks are subjected to intense heat and pressure. The rocks change (undergo metamorphosis ) to become a new type of rock. Marble , for example, is a metamorphic rock created from rock that was once limestone, a sedimentary rock.

Earth’s Evolution

Earth and the rest of the solar system formed about 4.6 billion years ago from a huge, spinning cloud of gas and dust.

Over a period of about 10 million years, the dense center of the cloud grew very hot. This massive center became the sun. The rest of the particles and objects continued to revolve around the sun, colliding with each other in clumps. Eventually, these clumps compressed into planets, asteroids , and moons. This process generated a lot of heat. 

Eventually, Earth began to cool and its materials began to separate. Lighter materials floated upward and formed a thin crust. Heavier materials sank toward Earth’s center. Eventually, three main layers formed: the core, the mantle, and the crust.

As Earth’s internal structure developed, gases released from the interior mixed together, forming a thick, steamy atmosphere around the planet. Water vapor condensed, and was augmented by water from asteroids and comets that continued to crash to Earth. Rain began to fall and liquid water slowly filled basins in Earth’s crust, forming a primitive ocean that covered most of the planet. Today, ocean waters continue to cover nearly three-quarters of our planet.

The end of Earth will come with the end of the sun. In a few billion years, the sun will no longer be able to sustain the nuclear reactions that keep its mass and luminosity consistent . First, the sun will lose more than a quarter of its mass, which will loosen its gravitational hold on Earth. Earth’s orbit will widen to about 1.7 AU. But the sun will also gain volume, expanding to about 250 times its current size. The sun in this red giant phase will drag Earth into its own fiery atmosphere, destroying the planet.

Eras on Earth

Paleontologists , geologists, and other scientists divide Earth’s history into time periods. The largest time period is the supereon , and only applies to one unit of time, the Precambrian . Eons , eras, and periods are smaller units of geologic time.

Most of Earth’s history took place in the Pre cambrian , which began when Earth was cooling and ended about 542 million years ago. Life began in the Precambrian, in the forms of bacteria and other single-celled organisms. Fossils from the Precambrian are rare and difficult to study. The Precambrian supereon is usually broken into three eons: the Hadean , the Archaean , and the Proterozoic .

We are currently living in the Phanerozoic eon.

The first major era of the Phanerozoic is called the Paleozoic, and the Cambrian is the first period of the Paleozoic era . “The Cambrian Explosion of Life ” was the rapid appearance of almost all forms of life. Paleontologists and geologists have studied fossils of archaea , bacteria, algae , fungi , plants, and animals that lived during the Cambrian period. The Cambrian was followed by the Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

The Mesozoic era began about 251 million years ago. This was the era when dinosaurs flourished . The Mezozoic has three periods: the Triassic, the Jurassic, and the Cretaceous.

We currently live in the Cenozoic era, which began about 65 million years ago. The Cenozoic is generally marked by three periods: the Paleogene, the Neogene, and the Quaternary . We live in the Quaternary period, which began about 2.5 million years ago. All ancestors of Homo sapiens (modern humans) evolved during the Quaternary.

Earth by the Numbers

Surface Gravity: 1 (one kilogram on Earth)

Orbital Period: 365.256 days

Satellites: 1 (the Moon)

Atmosphere: nitrogen (78%), oxygen (21%), argon, carbon dioxide, neon

Average Temperature: 15° Celsius (77 Kelvin, 59° Fahrenheit)

Ingredients for Life Scientists have gathered enough information about other planets in our solar system to know that none can support life as we know it. Life is not possible without a stable atmosphere containing the right chemical ingredients for living organisms: hydrogen, oxygen, nitrogen, and carbon. These ingredients must be balanced—not too thick or too thin. Life also depends on the presence of water. Jupiter, Saturn, Uranus, and Neptune all have atmospheres made mostly of hydrogen and helium. These planets are called gas giants, because they are mostly made of gas and do not have a solid outer crust. Mercury and Mars have some of the right ingredients, but their atmospheres are far too thin to support life. The atmosphere of Venus is too thick—the planet's surface temperature is more than 460 degrees Celsius (860 degrees Fahrenheit). Jupiter's moon Europa has a thin atmosphere rich with oxygen. It is likely covered by a huge ocean of liquid water. Some astrobiologists think that if life exists elsewhere in the solar system, it will be near vents at the bottom of Europa's ocean.

Earth to Earth Earth is the only planet in the solar system not named for a Greek or Roman deity. "Earth" originally meant the soil and land of our planet. (This is still what it means when the word is lowercase.) Eventually, Earth came to mean the planet itself.

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Related Resources

Planet Earth: Everything you need to know

Earth is the only planet known to support life. Learn about what Earth is made of and where it came from.

• Earth's orbit
• Earth's formation

Earth FAQs answered by an expert

• Earth's core
• Earth's magnetosphere

Earth's atmosphere

• Earth's composition

Earth's moon

Earth observation, life on earth.

Earth, our home, is the third planet from the sun . While scientists continue to hunt for clues of life beyond Earth, our home planet remains the only place in the universe where we've ever identified living organisms. 

Earth is the fifth-largest planet in the solar system. It's smaller than the four gas giants — Jupiter , Saturn , Uranus and Neptune — but larger than the three other rocky planets, Mercury , Mars and Venus .

Earth has a diameter of roughly 8,000 miles (13,000 kilometers) and is mostly round because gravity generally pulls matter into a ball. But the spin of our home planet causes it to be squashed at its poles and swollen at the equator, making the true shape of the Earth an "oblate spheroid."

Related: How big is Earth?

Our planet is unique for many reasons, but its available water and oxygen are two defining features. Water covers roughly 71% of Earth's surface, with most of that water located in our planet's oceans. About a fifth of Earth's atmosphere consists of oxygen, produced by plants. 

Related: 15 places on Earth that look exoplanetary

Planet Earth's orbit around the sun

While Earth orbits the sun, the planet is simultaneously spinning around an imaginary line called an axis that runs through the core, from the North Pole to the South Pole. It takes Earth 23.934 hours to complete a rotation on its axis and 365.26 days to complete an orbit around the sun — our days and years on Earth are defined by these gyrations.

Earth's axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through the planet's orbit around the sun. This means the Northern and Southern Hemispheres will sometimes point toward or away from the sun depending on the time of year, and this changes the amount of light the hemispheres receive, resulting in the changing seasons .

Earth happens to orbit the sun within the so-called " Goldilocks zone ," where temperatures are just right to maintain liquid water on our planet's surface. Earth's orbit is not a perfect circle, but rather a slightly oval-shaped ellipse, similar to the orbits of all the other planets in our solar system. Our planet is a bit closer to the sun in early January and farther away in July, although this proximity has a much smaller effect on the temperatures we experience on the planet's surface than does the tilt of Earth's axis. 

Statistics about Earth's orbit, according to NASA :

• Average distance from the sun : 92,956,050 miles (149,598,262 km)
• Perihelion (closest approach to the sun): 91,402,640 miles (147,098,291 km)
• Aphelion (farthest distance from the sun): 94,509,460 miles (152,098,233 km)
• Length of solar day (single rotation on its axis): 23.934 hours
• Length of year (single revolution around the sun): 365.26 days
• Equatorial inclination to orbit: 23.4393 degrees

How did Earth form?

Scientists think Earth was formed at roughly the same time as the sun and other planets some 4.6 billion years ago when the solar system coalesced from a giant, rotating cloud of gas and dust known as the solar nebula . As the nebula collapsed under the force of its own gravity, it spun faster and flattened into a disk. Most of the material in that disk was then pulled toward the center to form the sun.

Other particles within the disk collided and stuck together to form ever-larger bodies, including Earth. Scientists think Earth started off as a waterless mass of rock .

"It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish," Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, previously told Space.com . 

However, analyses of minerals trapped within ancient microscopic crystals suggest that there was liquid water already present on Earth during its first 500 million years, Marchi said.

Radioactive materials in the rock and increasing pressure deep within the Earth generated enough heat to melt the planet's interior, causing some chemicals to rise to the surface and form water, while others became the gases of the atmosphere. Recent evidence suggests that Earth's crust and oceans may have formed within about 200 million years after the planet took shape.

Related: 10 Earth impact craters you must see

We asked Jack Wright an ESA Internal Research Fellow a few commonly asked questions about our planet, Earth.  

Jack Wright, is an Internal Research Fellow with the European Space Agency (ESA).  

What sets Earth apart from other planets in the solar system?

From what we know so far, Earth is the only planet that hosts life and the only one in the Solar System with liquid water on the surface. Earth is also the only planet in the solar system with active plate tectonics, where the surface of the planet is divided into rigid plates that collide and move apart, causing earthquakes , mountain building, and volcanism. Sites of volcanism along Earth's submarine plate boundaries are considered to be potential environments where life could have first emerged. 

What makes our planet uniquely suitable to host life?

Earth is the right distance from the sun, such that liquid water has been stable in significant volumes over much of the planet's lifetime. It has the right chemical ingredients for life (e.g. water and carbon), and chemical cycling (such as between the planet's interior and oceans by volcanism and other geological activity) provides chemical pathways for life to extract energy to survive. 

Additional factors that have allowed the evolution of complex life are an oxygenated atmosphere, and protection from solar radiation by its magnetic field.

Which planet is closest to Earth in terms of distance?

New findings show that considering the average distance, Mercury is the nearest planet to Earth; considering the smallest possible distance, instead, Venus is closest. 

Is Mercury the most similar to ours in the solar system?

No. Mercury has no atmosphere and it has an old surface covered in impact craters, so it is very unlike Earth. One similarity is that Mercury and Earth both have internally generated magnetic fields. Venus and Earth are very similar in size. There is emerging evidence for active volcanism on Venus, however, its atmosphere is up to 100 times denser than Earth's and is mostly carbon dioxide with sulfuric acid clouds. The surface of Saturn's moon Titan physically resembles Earth's, with mountains, rivers, lakes, and seas. The difference is that Titan's mountains are made from water ice, which is as strong as rock under its surface temperature (-180°C), and the rivers and seas are full of hydrocarbons.

How many planets in the Milky Way could have conditions like Earth?

Scientists estimated that 1 in 5 stars like our sun has one Earth-like planet orbiting around them, which may support life. Considering that there are more than 200 billion stars in our Milky Way, there might be an estimated 40 billion planets that might support life in our galaxy. 

Why is it vital to preserve our planet?

Earth observation from space provides objective coverage across both space and time. The same space-based sensor gathers data from sites across the world, including places too remote or otherwise inaccessible for ground-based data acquisition.

And because Earth observation satellites remain in place for long periods of time, they can highlight environmental changes occurring gradually. Looking back through archived satellite data shows us the steady clearing of the world's rainforests, an apparent annual rise in sea level approaching 2 mm a year, and the increase of atmospheric pollution.

In the long term, this monitoring of the Earth's environment will enable a reliable assessment of the global impact of human activity and the likely future extent of climate change.

The scientific evidence of global climate change is irrefutable. The consequences of a warming climate are far-reaching  —  affecting freshwater resources, global food production, and sea level and triggering an increase in extreme weather events. In order to tackle climate change, scientists and decision-makers need reliable data to understand how our planet is changing.

For more than three decades, Earth-observing satellites have been providing the facts needed to address the challenges of our changing world.

Earth is the only naturally habitable planet for complex (e.g. human) life in the solar system. The consequences of a warming climate are far-reaching and are already threatening some people's ways of life and damaging wider biodiversity. If Earth becomes uninhabitable we have nowhere else to go. Colonizing the Moon and Mars is no substitute for preserving Earth. The Moon and Mars cannot sustain Earth's population of humans and other organisms.

Earth's internal structure

Earth's core is about 4,400 miles (7,100 km) wide, slightly larger than half the Earth's diameter and about the same size as Mars. The outermost 1,400 miles (2,250 km) of the core are liquid, while the inner core is solid. That solid core is about four-fifths as big as Earth's moon, at some 1,600 miles (2,600 km) in diameter. The core is responsible for the planet's magnetic field , which helps to deflect harmful charged particles shot from the sun. 

Above the core is Earth's mantle, which is about 1,800 miles (2,900 km) thick. The mantle is not completely stiff but can flow slowly. Earth's crust floats on the mantle much as a piece of wood floats on water. The slow motion of rock in the mantle shuffles continents around and causes earthquakes, volcanoes and the formation of mountain ranges.

Related: Earth's layers: Exploring our planet inside and out

Above the mantle, Earth has two kinds of crust. The dry land of the continents consists mostly of granite and other light silicate minerals, while the ocean floors are made up mostly of a dark, dense volcanic rock called basalt. Continental crust averages some 25 miles (40 km) thick, although it can be thinner or thicker in some areas. Oceanic crust is usually only about 5 miles (8 km) thick. Water fills in low areas of the basalt crust to form the world's oceans.

Earth gets warmer toward its core. At the bottom of the continental crust, temperatures reach about 1,800 degrees Fahrenheit (1,000 degrees Celsius), increasing about 3 degrees F per mile (1 degree C per km) below the crust. Geologists think the temperature of Earth's outer core is about 6,700 to 7,800 degrees F (3,700 to 4,300 degrees C) and that the inner core may reach 12,600 degrees F (7,000 degrees C) — hotter than the surface of the sun.

Earth's magnetic field

Earth's magnetic field is generated by currents flowing in Earth's outer core. The magnetic poles are always on the move, with the magnetic North Pole accelerating its northward motion to 24 miles (40 km) annually since tracking began in the 1830s. It will likely exit North America and reach Siberia in a matter of decades.

Earth's magnetic field is changing in other ways, too. Globally, the magnetic field has weakened 10 percent since the 19th century, according to NASA . 

But these changes are mild compared to what Earth's magnetic field has done in the past. A few times in every million years or so, the field completely flips, with the North and the South poles swapping places. The magnetic field can take anywhere from 100 to 3,000 years to complete the flip, Space.com previously reported .

The strength of Earth's magnetic field decreased by about 90 percent when a field reversal occurred in ancient past, according to Andrew Roberts, a professor at the Australian National University. The drop makes the planet more vulnerable to solar storms and radiation, which could significantly damage satellites as well as communication and electrical infrastructure.

"Hopefully, such an event is a long way in the future and we can develop future technologies to avoid huge damage," Roberts said in a statement .

When charged particles from the sun get trapped in Earth's magnetic field, they smash into air molecules above the magnetic poles, causing them to glow. This phenomenon is known as the auroras , the northern and southern lights.

Earth's atmosphere is roughly 78 percent nitrogen and 21 percent oxygen, with trace amounts of water, argon, carbon dioxide and other gases. No other planet in the solar system has an atmosphere loaded with free oxygen, which is vital to one of the other unique features of Earth: life.

Air surrounds Earth and becomes thinner farther from the surface. Roughly 100 miles (160 km) above Earth, the air is so thin that satellites can zip through the atmosphere with little resistance. Still, traces of atmosphere can be found as high as 370 miles (600 km) above the planet's surface.

The lowest layer of the atmosphere is known as the troposphere, which is constantly in motion and why we have weather. Sunlight heats the planet's surface, causing warm air to rise into the troposphere. This air expands and cools as air pressure decreases, and because this cool air is denser than its surroundings, it then sinks and gets warmed by the Earth again.

Above the troposphere, some 30 miles (48 km) above the Earth's surface, is the stratosphere. The still air of the stratosphere contains the ozone layer, which was created when ultraviolet light caused trios of oxygen atoms to bind together into ozone molecules. Ozone prevents most of the sun's harmful ultraviolet radiation from reaching Earth's surface, where it can damage and mutate life.

Water vapor, carbon dioxide and other gases in the atmosphere trap heat from the sun, warming Earth. Without this so-called " greenhouse effect ," Earth would probably be too cold for life to exist, although a runaway greenhouse effect led to the hellish conditions of Venus' current surface.

Earth-orbiting satellites have shown that the upper atmosphere actually expands during the day and contracts at night due to heating and cooling.

Earth's chemical composition

Oxygen is the most abundant element in rocks in Earth's crust, composing roughly 47 percent of the weight of all rock. The second most abundant element is silicon , at 27 percent, followed by aluminum , at 8 percent; iron , at 5%; calcium , at 4%; and sodium , potassium and magnesium , at about 2% each.

Earth's core consists mostly of iron and nickel and potentially smaller amounts of lighter elements, such as sulfur and oxygen. The mantle is made of iron and magnesium-rich silicate rocks (the combination of silicon and oxygen is known as silica, and minerals that contain silica are known as silicate minerals).

Earth's moon is 2,159 miles (3,474 km) wide, about one fourth of Earth's diameter. Our planet has one moon, while Mercury and Venus have none and all the other planets in our solar system have two or more.

The leading explanation for how Earth's moon formed is that a giant impact knocked the raw ingredients for the moon off the primitive, molten Earth and into orbit. Scientists have suggested that the object that hit the planet had roughly 10% the mass of Earth — about the size of Mars.

Astronauts and scientists have learned a lot about our planet by leaving it. From 240 miles (408 kilometers) away, aboard the International Space Station (ISS), astronauts are able to observe the thin, fragile atmosphere of Earth. 

Meanwhile, satellites orbiting Earth can track the planet's responses to changes —caused naturally and by humans– on a greater scale. Satellites have been launched to detect changes in the hole in the ozone layer, monitor cloud coverage and weather patterns and manage humans' use of Earth's resources. 

Earth is the only planet in the universe known to possess life. The planet boasts several million described species, living in habitats ranging from the bottom of the deepest ocean to a few miles up into the atmosphere. Researchers think far more species remain that have yet to be described to science.

Researchers suspect that other candidates for hosting life in our solar system — such as Saturn's moon Titan or Jupiter's moon Europa — could house primitive living creatures. Scientists have yet to precisely nail down exactly how our primitive ancestors first showed up on Earth, although most believe that a chemical soup on the planet gave rise to the building blocks of living organisms. (The precise set of circumstances necessary to create life from a lifeless planet are pretty unlikely, according to previous Space.com report , so it seems we got very lucky.)

Read more from Live Science: How did life arise on Earth?

Another theory suggests that life first evolved on the nearby planet Mars, which could once have been habitable, then traveled to Earth on meteorites hurled from the Red Planet by impacts from other space rocks.

"It's lucky that we ended up here, nevertheless, as certainly Earth has been the better of the two planets for sustaining life," biochemist Steven Benner, of the Westheimer Institute for Science and Technology in Florida, told Space.com . "If our hypothetical Martian ancestors had remained on Mars, there might not have been a story to tell."

Additional resources

• Read more about our planet in " A Brief History of Earth: Four Billion Years in Eight Chapters " (Custom House, 2021) by Andrew H. Knoll.
• Check out NASA 's page all about planet Earth.
• Consider a different perspective from Discover Magazine about what makes Earth unique: its minerals.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

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Charles Q. Choi is a contributing writer for Space.com and Live Science. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica. Visit him at http://www.sciwriter.us

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15 Earth Characteristics

The Earth is filled with a rich diversity of life. What makes the Earth such a habitable oasis for life? The planets Venus, Earth, and Mars all started out with atmospheres, and yet they evolved into vastly different worlds today. Certain features unique to the Earth, such as plate tectonics, have enabled it to be a dynamic world with oceans and a climate hospitable for life. By identifying the characteristics that make Earth hospitable, we can gain insight into what properties to look for on exoplanets that may point to the possibility of life.

Learning Objectives

By the end of this chapter, you will be able to:

• Discuss the Earth’s density and surface gravity and how it compares to the other planets in our solar system
• Explain the differentiation of Earth and its main interior layers
• Discuss how heat is generated inside a planet and how it is lost to cooling.
• Discuss the importance of plate tectonics for Earth’s habitability
• Explain how Earth’s magnetosphere protects life on Earth

The size of a world and distance it orbits its host star can take us very far in assessing whether the world could host life. We say more in the chapter on Habitable Zones about how the distance of the Earth from the Sun keeps the Earth at the right temperature for liquid water — and makes Venus too hot today for liquid water — and we will focus here on the bulk properties of the Earth.

Bulk Properties of the Earth

Side Note: The experiments of the ancient Greeks show how much can be determined with basic high-school mathematics.  Before you decide that something is unknowable, pause and think about how you could make a reasonable estimate, even within a factor of 10 (an “order of magnitude”). This habit of making estimates will make you a powerful problem-solver in science, business, and life.

In the early 18th century (and with the benefit of insights from Isaac Newton about the laws of gravity) Henry Cavendish “weighed the Earth” in his lab by cleverly measuring the acceleration of gravity on Earth. Gravity is a property of mass and Cavendish calculated a bulk density for the Earth of 5.48 g/cm 3 , very close to the currently known value of 5.515 g/cm 3 .

The density of a planet can easily be calculated if the radius and mass are known, quantities that can be measured even for planets orbiting other stars. The density of a planet gives immense insight into that world. All terrestrial planets in our solar system have higher densities than the jovian gas giants. The average density of the terrestrial planets is 5.0 g/cm 3 , while the average density for the jovian gas giants is 1.2 g/cm 3 . Exoplanets with densities that fall in between these values are commonly found and point toward intermediate types of planets that are not found in our solar system. For example, the “mini-Neptune” K2-18 b has an estimated density of 2.6 g/cm 3 .

Worked Example: Calculating the density of a planet

Looking up the mass and radius of the Earth, and using the density equation we find:

This tells us that an average cubic meter of the Earth contains 5500 kg, or 5.5 metric tons of matter.  A cubic meter is about the size of a washing machine. If 5.5 tons seems heavier than you would have guessed, it is because the core density of Earth is greater than the dirt and rocks on the surface of our planet.

7.9 — the Earth is almost 8 times more dense than Saturn

The fact that smaller worlds lose their internal heat (or cool off) more quickly than larger worlds is a fundamental reason why the Earth is hospitable to life. The Earth still has heat inside that can power geological activities such as plate tectonics that stabilize our atmosphere.

Earth’s Interior

How do we know about the interior structure of Earth, since we live on the surface? We can only drill a few kilometers before the temperature and pressure become too high to continue. The deepest manmade hole on Earth is the aptly named the Kola Superdeep Borehole, which reaches down to 12.3 km (7.6 miles).

Almost everything else we know about the interior of the Earth comes from seismic waves. Seismic waves carry the energy from events like earthquakes or volcanic eruptions. Seismic waves compress the elastic interior of the Earth like sound waves compress the air. The speed of seismic waves depends on the depth and density of medium. The fastest moving P-waves compress material in the direction that they travel. They are the first to arrive at seismic stations and travel through the core of the Earth. Sheering S-waves are slower and do not propagate through liquid material; they are blocked by the liquid core of the Earth. Slower still, R-waves ripple along the surface of the Earth. They arrive last at the seismic stations but have the potential to do the most damage.

Seismic waves reveal the bulk density structure of the Earth, as depicted in Figure 2 below. The core is about half the radius of the Earth and is comprised of an inner core that is about the size of the moon, surrounded by a molten iron core. The liquid core is also an important factor in the Earth’s habitability, as it enables the Earth to have a protective magnetosphere surrounding it. The thick rocky mantle wraps around the core and extends for the other half of the Earth radius. The outer shell is a thin crust of low density rock called the lithosphere.

All terrestrial planets in our solar system appear to have a similar layered structure inside, with a dense metal core at the center surrounded by the mantle and crust. This layered structure occurs because the planet cools over time and as it cools, the process of differentiation occurs, where the densest materials (like iron) sink to the center and the lightest materials float to the surface. A simple real world example shows this to be an intuitive process. If you shake oil and water together in a container, they will initially be in a mixture. However, over time, the denser water sinks to the bottom of the container and the lighter oil rises to the top.

One feature that distinguishes Earth from the other terrestrial planets is its crust. The Earth’s crust comprises two types: continental crust and oceanic crust. These are the tectonics plates that literally float and move around on top of the mantle, specifically on top of the asthenosphere. Earth is the only terrestrial planet that has oceanic crust so this gives us a clue that plate tectonics may be an important consideration when assessing the habitability of an exoplanet.

Sources of Planetary Heat

The Earth is a geologically active planet. Plate tectonics has already been mentioned as one of the unique properties that the Earth has compared to the other terrestrial planets in our solar system and a source of heat is required to drive this geological activity. There are a few possible origins for heat inside of a planet: accretion energy, differentiation  and  radioactive decay .

Planets form by accreting planetesimals that collide and stick together to form larger bodies. These collisions generate significant amounts of heat or accretion energy as the planet is assembled.  However, all of the heat from accretion energy is injected during the early stages of planet formation.

As material sinks during differentiation , energy is conserved as gravitational potential energy is converted first to energy of motion (kinetic energy) and then to heat (thermal energy).

Over time, as differentiation is complete and accretion is much less frequent, radioactivity becomes and remains the main source of interior heat for a planet (we note here that the large jovian planets still have heat from their formation in their voluminous interiors). Radioactivity is a natural process in which heavy nuclei spontaneously break apart; when the nuclei break apart into smaller ones, energy is emitted. All planets in our solar system contained the same chemical mixture from the solar nebula at early times, and these include some heavy radioactive elements such as uranium ( 238 U) and potassium ( 40 K).

Radioactivity continues to supply internal heat to the Earth to fuel geological activity, yet Mercury and the Moon are geologically dead. The difference here goes back to the cooling rate of a planet. Smaller planets lose their heat faster than larger ones. Therefore, the size of a world is an important indicator of the potential for geological activity. Before describing types of geological activity, let’s consider exactly how heat escapes from inside of a planet.

Heat Loss From a Planet

The interior heat of a world can be lost via several mechanisms: convection , conduction , and radiation . When heat from the core moves to the lower mantle boundary, convection cells are set up inside of the mantle. Convection is the familiar process wherein hot material, such as air, rises as cooler material sinks. Convection, in which energy is transported from a warm region, such as the interior of Earth, to a cooler region, such as the upper mantle, is a process we encounter often in astronomy—in stars as well as planets. You can see convection in action when boiling a pot of water on a stove. As the water heats up from below and starts to boil, convection cells are set up in the water, as seen in Figure 3. Once the heat reaches the top of the mantle, it then moves through the crust via conduction. Finally, the heat makes it to the Earth’s surface and is radiated away into space (or, to be specific, in the case of planets with atmospheres, like the Earth and Venus, the heat must travel through this layer first).

Now that the mechanisms for generating heat inside a planet, as well as how that heat gets out of a planet, are understood, we can move on to discuss the different types of geological activity that can be driven by this internal heat.

Plate Tectonics

The size of the Earth, specifically its radius, is fundamentally the reason why the Earth is still geologically active: there is enough internal heat inside our relatively large planet to drive geological activity. A smaller terrestrial planet, such as Mercury, is too small to retain enough heat to sustain any geological activity: Mercury cooled off fast and is now geologically inactive.

An important property of Earth is that it has plate tectonics. Plate tectonics explains how slow motions within the mantle of Earth move large segments of the crust, resulting in a gradual “drifting” of the continents as well as the formation of mountains and other large-scale geological features. The power to move the plates is provided by slow convection  of the mantle, a process by which heat escapes from the interior through the upward flow of warmer material and the slow sinking of cooler material.

While Venus and Mars are likely to also have convection in their mantles, Earth is the only planet in our solar system known to have plate tectonics. Geological evidence suggests that plate tectonics began operating on the Earth about 3.8 billion years ago. The upper rocky layer of the Earth is divided into about twelve major tectonic plates that float on top of the convecting mantle, shown in Figure 4. The distribution of these plates affect global climate because continental crust has a higher albedo (reflects more light) than ocean water. Continental crust was thought to have a maximum extent between 1.6 – 2.7 billion years ago, causing ice ages and high rates for burial of organic material in the early and late Proterozoic eon.

Plate tectonics provide a mechanism for circulating material between the surface of the planet and Earth’s interior. Plates pull apart from each other along rift zones, such as the Mid-Atlantic ridge, driven by upwelling currents in the mantle. Subduction zones form at boundaries where one edge of an approaching plate moves under another. These recycling zones are critical for life on our planet. They are part of a negative feedback loop that stabilizes our climate thanks to chemical interactions between surface rocks and the atmosphere. Rain removes carbon dioxide from the atmosphere and stores it as calcium carbonate in surface rocks through a weathering process. Carbon-enriched rocks are then transported into the deep mantle along the subduction zones, removing excess CO 2 from the atmosphere. The flow of material goes the other way as well; some elements are transported from the mantle to the surface of the planet.

Volcanoes are also formed through plate tectonics. When volcanoes erupt, gasses trapped inside of the Earth are released. This process of volcanic outgassing supplies the raw materials for the Earth’s atmosphere (Figure 6). The primary materials that are outgassed include water vapor, CO 2 , N 2 , and SO 2 . Some of these gasses are greenhouse gases and contribute to maintaining the energy balance of the Earth. Plate tectonics on Earth allows carbon to be cycled from the atmosphere, down to carbonate rocks on the ocean floor, and back into the atmosphere through volcanism. This carbon cycle is an essential part of maintaining a hospitable atmosphere on Earth. Other planets in our solar system experience tectonic stresses, but plate tectonics – with the active movement of crustal and oceanic plates – is unique to Earth. When exploring exoplanets that may be conducive to life, the presence of plate tectonics would be a favorable condition, at least based on our experience on Earth.

Earth’s Magnetosphere

The core of the Earth has a temperature similar to the surface of the Sun. This heat ionizes the molten iron, producing charged particles. As the liquid metal inside Earth circulates, the charged particles set up an electric current. When many charged particles are moving together like that—in the laboratory or on the scale of an entire planet—they produce a magnetic field. Earth’s magnetic field extends thousands of miles above the surface of the planet.

Our planet behaves in some ways as if a giant bar magnet were inside it, aligned approximately with the rotational poles of Earth.  When charged particles from the surface of the Sun (the “solar wind”) are directed toward us, the Earth’s magnetic field deflects them and shields the planet. This region, called the magnetosphere , is defined as the zone within which Earth’s magnetic field dominates over the weak interplanetary magnetic field that extends outward from the Sun (Figure 7). The magnetosphere plays an important role for habitability, by preventing stripping of our atmosphere.

For a planet to have a magnetic field, it must have a liquid metallic layer and it must also be spinning fast enough to create a turbulent flow. Jupiter meets both of those conditions — it has a liquid conducting layer made of liquid metallic hydrogen in its outer core and it rotates once every 11 hours — and has the strongest magnetic fields in our solar system. Although Venus has a liquid metallic outer core like the Earth, it rotates too slowly on its axis (once ever 243 days) to generate a magnetic field. When assessing the habitability of an exoplanet, we want to determine whether it has the conditions to set up a protective magnetosphere.

There is evidence in Earth’s geologic record from magnetic minerals that many magnetic pole reversals have occurred in the past and some scientists believe that the magnetic fields are beginning to collapse and flip again . Life has existed on our planet for billions of years, and no correlation has been found between mass extinctions and magnetic pole reversals. The risk to life during a magnetic pole reversal may be modest, but the risk to power grids that modern humans depend upon will be more substantial.

Earth’s Habitability

We have looked at some of the properties of Earth that contribute to making it a habitable world. We began this chapter by stating that the Earth’s size and distance together can explain some of the unique properties that make Earth habitable. The Earth has a large enough size to have heat inside of it, initially from accretion and differentiation, but mainly from radioactivity today. As this heat escapes from the Earth, it is carried from the lower to the upper mantle through convection. This heat at the upper mantle powers plate tectonics, which is responsible for maintaining a continuous cycle between the Earth’s atmosphere and the crust, thus setting up a stable climate. One of the Earth’s differentiated layers is the liquid outer core, and this layer combined with Earth’s rotation rate sets up a protective magnetosphere around our planet.

Key Concepts and Summary

The Earth formed through the collision of planetesimals in our solar system when the Sun was forming more than 4.5 Gya. The planetesimal collisions deposited frictional accretion energy in the interior of our planet and heavier elements in the molten young Earth began to settle toward the core, differentiating into layers. The frictional processes of differentiation delivered an additional boost of energy to the interior. Today, Earth has a solid iron core surrounded by a molten liquid outer metal core. Turbulence in the outer core is coupled with rotation of the planet to generate a global magnetic field that shields the atmosphere from being eroded by the fast-moving particles in the solar wind.  The energy of accretion and differentiation were one-time processes that deposited internal heat to the planet long ago. Now, an additional source of energy comes from the radioactive decay of heavy elements. The internal heat beneath the lithosphere drives motion of the floating continental plates.  Planets lose internal heat over time (with smaller planets cooling faster).

Review Questions

Summary questions.

• What two properties of a world determine its density?
• How does the density of the Earth compare with the other planets in our solar system?
• How does surface gravity differ from density?
• Can a planet with a low surface gravity hold on to an atmosphere?
• Where did heat inside the Earth come from initially? What is the main source of heat from inside the Earth today?
• How can heat escape from inside a planet to the surface?
• What property of a planet determines how quickly it will lose its interior heat?
• Which planet cools faster: Earth or Mars? Explain.
• How does plate tectonics contribute to Earth’s habitability?
• Can a planet without plate tectonics be habitable?
• How does Earth’s magnetosphere protect life?

Astrobiology Copyright © by Debra Fischer; Allyson Sheffield; Joshua Tan; and Lily Ling Zhao is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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What is Earth?

Earth is the third planet from the Sun and the fifth largest planet in the solar system in terms of size and mass. Its near-surface environments are the only places in the universe known to harbour life.

Where is Earth in the Milky Way Galaxy?

Earth is located in the Orion-Cygnus Arm, one of the four spiral arms of the Milky Way , which lies about two-thirds of the way from the centre of the Galaxy.

What is Earth named for?

Earth’s name in English, the international language of astronomy , derives from Old English and Germanic words for ground and earth , and it is the only name for a planet of the solar system that does not come from Greco-Roman mythology.

What was Earth like when it was first formed?

Earth and the other planets in the solar system formed about 4.6 billion years ago. The early Earth had no ozone layer and no free oxygen, lacked oceans, and was very hot.

Viewed from another planet, Earth would appear bright and bluish in colour. In latitudinal belts, swirling white cloud patterns of midlatitude and tropical storms can be seen. The polar regions would appear white because of ice, the oceans a dark blue-black, the deserts a tawny beige, and forests and jungles a vibrant green.

Recent News

Earth , third planet from the Sun and the fifth largest planet in the solar system in terms of size and mass. Its single most outstanding feature is that its near-surface environments are the only places in the universe known to harbour life. It is designated by the symbol ♁. Earth’s name in English , the international language of astronomy , derives from Old English and Germanic words for ground and earth , and it is the only name for a planet of the solar system that does not come from Greco-Roman mythology. Earth is part of the " observable universe ," the region of space that humans can actually or theoretically observe with the aid of technology . Unlike the observable universe, the universe is possibly infinite .

Since the Copernican revolution of the 16th century, at which time the Polish astronomer Nicolaus Copernicus proposed a Sun-centred model of the universe ( see heliocentric system ), enlightened thinkers have regarded Earth as a planet like the others of the solar system. Concurrent sea voyages provided practical proof that Earth is a globe, just as Galileo ’s use of his newly invented telescope in the early 17th century soon showed various other planets to be globes as well. It was only after the dawn of the space age, however, when photographs from rockets and orbiting spacecraft first captured the dramatic curvature of Earth’s horizon , that the conception of Earth as a roughly spherical planet rather than as a flat entity was verified by direct human observation. Humans first witnessed Earth as a complete orb floating in the inky blackness of space in December 1968 when Apollo 8 carried astronauts around the Moon . Robotic space probes on their way to destinations beyond Earth, such as the Galileo and the Near Earth Asteroid Rendezvous (NEAR) spacecraft in the 1990s, also looked back with their cameras to provide other unique portraits of the planet.

Viewed from another planet in the solar system, Earth would appear bright and bluish in colour. Easiest to see through a large telescope would be its atmospheric features, chiefly the swirling white cloud patterns of midlatitude and tropical storms , ranged in roughly latitudinal belts around the planet . The polar regions also would appear a brilliant white, because of the clouds above and the snow and ice below. Beneath the changing patterns of clouds would appear the much darker blue-black oceans, interrupted by occasional tawny patches of desert lands. The green landscapes that harbour most human life would not be easily seen from space. Not only do they constitute a modest fraction of the land area, which itself is less than one-third of Earth’s surface, but they are often obscured by clouds . Over the course of the seasons, some changes in the storm patterns and cloud belts on Earth would be observed. Also prominent would be the growth and recession of the winter snowcap across land areas of the Northern Hemisphere.

Scientists have applied the full battery of modern instrumentation to studying Earth in ways that have not yet been possible for the other planets; thus, much more is known about its structure and composition . This detailed knowledge, in turn, provides deeper insight into the mechanisms by which planets in general cool down, by which their magnetic fields are generated, and by which the separation of lighter elements from heavier ones as planets develop their internal structure releases additional energy for geologic processes and alters crustal compositions .

Earth’s surface is traditionally subdivided into seven continental masses: Africa , Antarctica , Asia , Australia , Europe , North America , and South America . These continents are surrounded by five major bodies of water: the Arctic , Atlantic , Indian , Pacific , and Southern oceans. However, it is convenient to consider separate parts of Earth in terms of concentric, roughly spherical layers. Extending from the interior outward, these are the core, the mantle, the crust (including the rocky surface), the hydrosphere (predominantly the oceans , which fill in low places in the crust), the atmosphere (itself divided into spherical zones such as the troposphere , where weather occurs, and the stratosphere , where lies the ozone layer that shields Earth’s surface and its organisms against the Sun ’s ultraviolet rays), and the magnetosphere (an enormous region in space where Earth’s magnetic field dominates the behaviour of electrically charged particles coming from the Sun).

Knowledge about these divisions is summarized in this astronomically oriented overview. The discussion complements other treatments oriented to the Earth sciences and life sciences. Earth’s figure and dimensions are discussed in the article geodesy . Its magnetic field is treated in the article geomagnetic field . The early evolution of the solid Earth and its atmosphere and oceans is covered in geologic history of Earth . The geologic and biological development of Earth, including its surface features and the processes by which they are created and modified, are discussed in geochronology , continental landform , and plate tectonics . The behaviour of the atmosphere and of its tenuous , ionized outer reaches is treated in atmosphere , while the water cycle and major hydrologic features are described in hydrosphere , ocean , and river . The solid Earth as a field of study is covered in geologic sciences , the methods and instruments employed to investigate Earth’s surface and interior are discussed in Earth exploration , and the history of the study of Earth from antiquity to modern times is surveyed in Earth sciences . The global ecosystem of living organisms and their life-supporting stratum are detailed in biosphere .

Earth: Facts about the Blue Planet

Find out how Earth formed, what it's made of and more.

Where is Earth located?

What is earth made of.

• Earth's atmosphere
• Earth characteristics

What makes Earth special?

Additional resources, bibliography.

Earth is our home planet, the only place in the universe where we know for certain that life exists. Earth formed over 4.6 billion years ago from a swirling cloud of gas and dust that gave rise to our entire solar system , including our star, the sun. Scientists hypothesize that this gas and dust collapsed into a disk, with different parts of the disk coalescing into each of the planets in the solar system .

Our planet sits in a small corner of the Milky Way galaxy, 25,000 light-years from the galactic center, according to NASA . The solar system is situated on a minor arm called the Orion Spur, which branches off from the Sagittarius Arm, one of the galaxy's two major spiral arms.

Earth's circumference is 24,901 miles (40,075 kilometers), making it the largest rocky planet in the solar system, according to Live Science sister site Space.com .  Our planet orbits 93 million miles (150,000 km) away from the sun, giving it the right temperature for persistent liquid water on the surface; it's the only known body to orbit in this so-called Goldilocks zone.  

Earth is composed of many elements, chief among them oxygen, silicon, magnesium, iron, aluminum and nickel, according to Caltech's Infrared Processing and Analysis Center . Our planet's crust is a thin outer layer, containing mostly silicate and basaltic rocks, that extends on average around 18 miles (30 km) below the planet's surface, according to the U.S. Geological Survey (USGS). The mantle is the next layer down, extending to about 1,800 miles (2,900 km) below Earth's surface. A common misconception is that all the rock in the mantle is melted into magma; in reality, most of it is in a highly viscous form that is so thick that it takes millions of years for its movement to become apparent. In Earth's center is a nickel-iron core that is liquid on the outside, down to 1,400 miles (2,250 km), but is crushed by incredible pressures into a solid form at the lowest depths, according to the USGS.

Earth has several enormous landforms. The largest continent, which is sometimes known as Afro-Eurasia (though more commonly broken up into Africa, Europe and Asia), has a total area of 32.8 million square miles (84.95 million square km), according to the Encyclopedia of World Geography . North and South America together constitute 16.43 million square miles (42.55 million square km), according to the online encyclopedia Nations Online , while the frozen continent of Antarctica is 5.41 million square miles (14 million square km). The area of Australia is 2.97 million square miles (7.66 million square km), according to the Australian government .

Processes below Earth's crust cause these continents to move around over geological time periods. Geologists have discovered underground continents buried deep below the surface, and though nobody quite knows how or when they formed, they may be as old as Earth itself.

What is Earth's atmosphere made of?

Our planet's atmosphere is 78% nitrogen, 20% oxygen, 0.9% argon and 0.04% carbon dioxide, plus trace amounts of other gases, according to NASA. Most human activity takes place in the lowest atmospheric layer, the troposphere, which extends 5 to 9 miles (8 to 14.5 km) over our heads, NASA says . Above that is the stratosphere, where clouds and weather balloons fly, going up to 31 miles (50 km). This is followed by the mesosphere, which extends up to 53 miles (85 km) in altitude (this is where meteors burn up), and the thermosphere, which reaches far into space, at least 373 miles (600 km) high.  

Human activity has a huge effect on climate and weather in Earth's atmosphere. By adding excess carbon dioxide, which traps infrared radiation from the sun, human industry is heating up our planet via global warming . In 2021, the United Nations announced that parts of the Arctic had reached a new temperature record in June 2020: 100 F (38 C) in the Siberian town of Verkhoyansk.

What are some characteristics of Earth?

Earth is tilted on its axis by 23.4 degrees, meaning that sunlight falls unevenly on the planet's surface over the course of the year, creating seasonal variation over most of the planet. But regions experience different variances in sunlight, so Earth's surface is often broken up into three major climatic zones: the polar regions in the Arctic and Antarctic, which start above or below 66 degrees latitude north or south; the middle temperate zones, between 23 and 66 degrees latitude north or south; and the tropical regions, between the Tropic of Cancer, at 23 degrees latitude north, and the Tropic of Capricorn, at 23 degrees latitude south, according to the National Oceanic and Atmospheric Administration .

The tallest point above sea level is the peak of Mount Everest, at 29,032 feet (8,849 meters), according to Britannica ). A crescent-shaped trough at the bottom of the western Pacific Ocean known as the Mariana Trench is the deepest spot on our planet, extending down to 36,037 feet (10,984 m). 

The Nile is the longest river in the world, winding for 4,132 miles (6,650 km) through northeastern Africa. Lake Baikal in Russia is the largest and deepest freshwater lake, containing 5,521 cubic miles of water (23,013 cubic km) — a volume approximately equivalent to that of all five North American Great Lakes combined.

Earth is unique because it is the only place in the universe known to host life. Some of the oldest evidence of microbial life suggests that it was already widespread on our planet 3.95 billion years ago, Live Science previously reported. Exactly how these microscopic creatures arose remains a mystery, though experts have proposed many theories .

Scientists estimate that there are as many as 1 trillion species on our planet , occupying niches that extend from the upper atmosphere to deep below the rocky surface. Bizarre and complex biospheres exist around hydrothermal vents at the ocean's bottom and in just about every rock and crevice ever explored, Live Science previously reported. Whether this means organisms exist elsewhere in the solar system or beyond remains an open question, but the diversity of life on Earth has given scientists hope that life might exist in extreme environments throughout the universe. 

• Learn how to measure Earth's shape and size in this blog post from physicist Matt Strassler.
• Explore NASA's latest information about Earth.
• Marvel at the beauty of our planet in this photo gallery from NASA.

Bishop, B. C. (2021, May 13). Mount Everest . Britannica. https://www.britannica.com/place/Mount-Everest  

Caltech Infrared Processing and Analysis Center. (n.d.). What is Earth made of? Cool Cosmos. Retrieved March 25, 2022, from https://coolcosmos.ipac.caltech.edu/ask/58-What-is-Earth-made-of-  

Geoscience Australia. (n.d.). Area of Australia - states and territories . Australian Government. Retrieved March 25, 2022, from https://www.ga.gov.au/scientific-topics/national-location-information/dimensions/area-of-australia-states-and-territories  

McColl, R. W. (Ed.). (2005). Encyclopedia of world geography . Facts on File. https://books.google.com/books?id=DJgnebGbAB8C&pg=PA215&redir_esc=y#v=onepage&q&f=false  

NASA. (1976). U.S. Standard Atmosphere, 1976 . NASA Technical Reports Server. https://ntrs.nasa.gov/citations/19770009539  

NASA Goddard Space Flight Center. (2015, December). The Milky Way galaxy . https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html  

National Oceanic and Atmospheric Administration. (n.d.). Teacher background information: Earth's climate [PDF]. https://gml.noaa.gov/infodata/lesson_plans/Teacher%20Background%20Information-%20Earth's%20Climate.pdf  

Nations Online. (n.d.). Countries of the Americas . Retrieved March 25, 2022, from https://www.nationsonline.org/oneworld/america.htm  

Robertson, E. C. (2011, January 14). The interior of the Earth . U.S. Geological Survey. ​​ https://pubs.usgs.gov/gip/interior/  

Sharp, T. (2021, July 6). How big is Earth? Space.com. https://www.space.com/17638-how-big-is-earth.html  

Sharp, T., & Urrutia, D. E. (2022, January 21). How far is Earth from the sun? Space.com. https://www.space.com/17081-how-far-is-earth-from-the-sun.html

Zell, H. (2017, August 7). Earth's atmospheric layers . NASA. https://www.nasa.gov/mission_pages/sunearth/science/atmosphere-layers2.html  

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Adam Mann is a freelance journalist with over a decade of experience, specializing in astronomy and physics stories. He has a bachelor's degree in astrophysics from UC Berkeley. His work has appeared in the New Yorker, New York Times, National Geographic, Wall Street Journal, Wired, Nature, Science, and many other places. He lives in Oakland, California, where he enjoys riding his bike. 

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