Earth
 Earth as seen from Meteosat-12 in 2025, during the March equinox | |||||||||
| Designations | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Adjectives |
| ||||||||
| Symbol | .svg){kind=small} and .svg){kind=small} [1] | ||||||||
| Orbital characteristics | |||||||||
| Epoch J2000[n 1] | |||||||||
| Aphelion | 152097597 km | ||||||||
| Perihelion | 147098450 km[n 2] | ||||||||
| 149598023 km[2] | |||||||||
| Eccentricity | 0.0167086[2] | ||||||||
| 365.256363004 d[3] (1.00001742096 aj) | |||||||||
Average orbital speed | 29.7827 km/s[4] | ||||||||
| 358.617° | |||||||||
| Inclination |
| ||||||||
| −11.26064° – J2000 ecliptic[4] | |||||||||
| 3 January 2026 | |||||||||
| 114.20783°[4] | |||||||||
| Satellites | 1, the Moon | ||||||||
| Physical characteristics | |||||||||
| 6371.0 km[6] | |||||||||
Equatorial radius | 6378.137 km[7][8] | ||||||||
Polar radius | 6356.752 km[9] | ||||||||
| Flattening | 1/298.257222101 (ETRS89)[10] | ||||||||
| Circumference |
| ||||||||
| Volume | 1.08321×1012 km3[4] | ||||||||
| Mass | (5.97217±0.00028)×1024 kg[13] | ||||||||
Mean density | 5.513 g/cm3[4] | ||||||||
| 9.80665 m/s2[14] (exactly 1 g0) | |||||||||
| 0.3307[15] | |||||||||
| 11.186 km/s[4] | |||||||||
1.0 d (24h 00 m 00s) | |||||||||
Equatorial rotation velocity | 1674.4 km/h[17] | ||||||||
| 23.4392811°[3] | |||||||||
| Albedo | |||||||||
| Temperature | 255 K (−18 °C) (blackbody temperature)[18] | ||||||||
| |||||||||
| Surface equivalent dose rate | 0.274 μSv/h[22] | ||||||||
| −3.99 | |||||||||
| Atmosphere | |||||||||
Surface pressure | 101.325 kPa (at sea level) | ||||||||
| Composition by volume |
| ||||||||
Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is made possible by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its ocean, which covers 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, which is predominantly located within Earth's land hemisphere in the form of continental landmasses. Most of Earth's land is at least somewhat humid and covered by vegetation, while large ice sheets at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers, and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation.
Earth has a dynamic atmosphere, which sustains Earth's surface conditions and protects it from most meteoroids and ultraviolet light at entry. It is composed primarily of nitrogen and oxygen. Water vapor is widely present in the atmosphere, forming clouds that cover most of the planet. The water vapor acts as a greenhouse gas and, together with other greenhouse gases in the atmosphere, particularly carbon dioxide (CO2), creates the conditions for both liquid surface water and water vapor to persist via the capturing of energy from the Sun's light. This process maintains the current average surface temperature of 14.76 °C (58.57 °F), at which water is liquid under normal atmospheric pressure. Differences in the amount of captured energy between geographic regions (as with the equatorial region receiving more sunlight than the polar regions) drive atmospheric and ocean currents, producing a global climate system with different climate regions, and a range of weather phenomena such as precipitation, allowing components such as carbon and nitrogen to cycle.
Earth is rounded into an ellipsoid with a circumference of about 40,000 kilometres (24,900 miles). It is the densest planet in the Solar System. Of the four rocky planets, it is the largest and most massive. Overall, Earth is the sixth largest object in the Solar System after the Sun and the outer planets. Earth is about eight light-minutes (1 AU) away from the Sun and orbits it, taking a year (about 365.25 days) to complete one revolution. Earth rotates around its own axis in slightly less than a day (in about 23 hours and 56 minutes). Earth's axis of rotation is tilted with respect to the perpendicular to its orbital plane around the Sun, producing seasons. Earth is orbited by one permanent natural satellite, the Moon, which orbits Earth at 384,400 km (238,855 mi)—1.28 light seconds—and is roughly a quarter as wide as Earth. The Moon's gravity helps stabilize Earth's axis, causes tides, and gradually slows Earth's rotation. Likewise, Earth's gravitational pull has already made the Moon's rotation tidally locked, keeping the same near side facing Earth.
Earth, like most other bodies in the Solar System, formed about 4.5 billion years ago from gas and dust in the early Solar System. The formation of the ocean and the subsequent development of life occurred during the first billion years of Earth's history. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago in Africa and have spread across every continent on Earth. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions.
Etymology
The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe.[23] It has cognates in every Germanic language, from which *erþō has been reconstructed. In its earliest attestation, the word eorðe was used to translate the many senses of Latin terra and Greek gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra (or Tellus) and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ('Earth'), a giantess often given as the mother of Thor.[24]
Historically, Earth has been written in lowercase. During the Early Middle English period, its definite sense as "the globe" began being expressed using the phrase the earth. By the period of Early Modern English, capitalization of nouns began to prevail, and the earth was also written the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets, though earth and forms with the earth remain common.[23] House styles now vary: Oxford spelling recognizes the lowercase form as the more common, with the capitalized form an acceptable variant. Another convention capitalizes Earth when appearing as a name, such as a description of the "Earth's atmosphere", but employs the lowercase when it is preceded by the, such as "the atmosphere of the earth". It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?"[25]
The name Terra /ˈtɛrə/ TERR-ə is occasionally used in scientific writing; it also sees use in science fiction to distinguish humanity's inhabited planet from others,[26] while in poetry Tellus /ˈtɛləs/ TELL-əs has been used to denote personification of the Earth.[27] Terra is also the name of the planet in some Romance languages, languages that evolved from Latin, like Italian and Portuguese, while in other Romance languages the word gave rise to names with slightly altered spellings, like the Spanish Tierra and the French Terre. The Latinate form Gaea (English: /ˈdʒiː.ə/ DJEE-ə) of the Greek poetic name Gaia ([ɡâi̯.a] or [ɡâj.ja]) is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is /ˈɡaɪ.ə/ GYE-ə rather than the more traditional English /ˈɡeɪ.ə/ GAY-ə.[28]
There are a number of adjectives for the planet Earth. The word earthly is derived from Earth. From the Latin Terra comes terran /ˈtɛrən/ TERR-ən,[29] terrestrial /təˈrɛstriəl/ tərr-EHST-ree-əl,[30] and (via French) terrene /təˈriːn/ tə-REEN,[31] and from the Latin Tellus comes tellurian /tɛˈlʊəriən/ teh-LUURR-ee-ən[32] and telluric.[33]
Natural history
Formation
The oldest material found in the Solar System is dated to 4.5682+0.0002
−0.0004 Ga (billion years) ago.[34] By 4.54±0.04 Ga, the primordial Earth had formed.[35] The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth being estimated as likely taking anywhere from 70 to 100 million years to form.[36]
Estimates of the age of the Moon range from 4.5 Ga to significantly younger.[37] The leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object with about 10% of Earth's mass, named Theia, collided with Earth.[38] It hit Earth with a glancing blow, and some of its mass merged with Earth.[39][40] Between approximately 4.0 and 3.8 Ga, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth.[41]
After formation
Earth's atmosphere and oceans were formed by volcanic activity and outgassing.[42] Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets.[43] Sufficient water to fill the oceans may have been on Earth since it formed.[44] In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity.[45] By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.[46]
As the molten outer layer of Earth cooled, it formed the first solid crust, which is thought to have been mafic in composition. The first continental crust, which was more felsic in composition, formed by the partial melting of this mafic crust.[48] Hadean-aged zircon grains found in Western Australia, dating back as far as 4.4 Ga, provide the oldest direct evidence of Earth's surface, indicating that felsic continental crust and liquid water existed within 140–160 million years of the planet's formation.[49] There are two main models of how this initial small volume of continental crust evolved to reach its current abundance:[50] (1) a relatively steady growth up to the present day,[51] which is supported by the radiometric dating of continental crust globally and (2) an initial rapid growth in the volume of continental crust during the Archean, forming the bulk of the continental crust that now exists,[52][53] which is supported by isotopic evidence from hafnium in zircons and neodymium in sedimentary rocks. The two models and the data that support them can be reconciled by large-scale recycling of the continental crust, particularly during the early stages of Earth's history.[54]
New continental crust forms as a result of plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form supercontinents that have subsequently broken apart. At approximately 750 Ma, one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia at 600–540 Ma, then finally Pangaea, which also began to break apart at 180 Ma.[55]
The most recent pattern of ice ages began about 40 Ma,[56] and then intensified during the Pleistocene about 3 Ma.[57] High- and middle-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 21,000, 41,000, and 100,000 years.[58] The Last Glacial Period, colloquially called the "last ice age", covered large parts of the continents, to the middle latitudes, in ice and ended about 11,700 years ago.[59]
Origin of life and evolution
Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose.[61] The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen (O2) accumulated in the atmosphere and, due to interaction with ultraviolet solar radiation, formed a protective ozone layer (O3) in the upper atmosphere.[62] The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.[63] True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized Earth's surface.[64] Among the earliest fossil evidence for life are microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia,[65] biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland,[66] and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia.[67][68] The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms.[69][70]
During the Neoproterozoic, 1000 to 539 Ma, much of Earth might have been covered in ice. This hypothesis has been termed "Snowball Earth", and it is of particular interest because it preceded the Cambrian explosion, when multicellular life forms significantly increased in complexity.[71][72] Following the Cambrian explosion, 535 Ma, there have been at least five major mass extinctions and many minor ones.[73] Apart from the proposed current Holocene extinction event, the most recent was 66 Ma, when an asteroid impact triggered the extinction of non-avian dinosaurs and other large reptiles, but largely spared small animals, such as insects, mammals, lizards, and birds. Mammalian life has diversified over the past 66 million years, and several million years ago, an African ape species gained the ability to stand upright.[74][75] This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the evolution of humans. The development of agriculture, and then civilization, led to humans having an influence on Earth and the nature and quantity of other life forms that continues to this day.[76]
Future
Earth's expected long-term future is tied to that of the Sun. Over the next 1.1 billion years, solar luminosity will increase by 10%, and over the next 3.5 billion years by 40%.[77] Earth's increasing surface temperature will accelerate the inorganic carbon cycle, possibly reducing CO2 concentration to levels lethally low for current plants (10 ppm for C4 photosynthesis) in approximately 100–900 million years.[78][79] A lack of vegetation would result in the loss of oxygen in the atmosphere, making current animal life impossible.[80] Due to the increased luminosity, Earth's mean temperature may reach 100 °C (212 °F) in 1.5 billion years, and all ocean water will evaporate and be lost to space, which may trigger a runaway greenhouse effect, within an estimated 1.6 to 3 billion years.[81] Even if the Sun were stable and eternal, a significant fraction of the water in the modern oceans would descend into the mantle, due to reduced steam venting from mid-ocean ridges as the core of the Earth slowly cools.[81][82]
The Sun will evolve to become a red giant in about 5 billion years. Models predict that the Sun will expand to roughly 1 AU (150 million km; 93 million mi), about 250 times its present radius.[77][83] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will move to an orbit 1.7 AU (250 million km; 160 million mi) from the Sun when the star reaches its maximum radius, otherwise, with tidal effects, it may enter the Sun's atmosphere and be vaporized, with the heavier elements sinking to the core of the dying sun.[77] A new study published in 2026 has suggested that the Earth is likely to survive the Sun's asymptotic giant branch phase.[84]
Composition and structure
Earth is a rocky planet and an ocean world, the only one in the Solar System with liquid surface water. Among all rocky Solar System objects, it is the most massive, 81 times that of Earth's Moon; and among all planetary-mass objects of the Solar System, it is the object with the highest density.[85]
Earth has a rounded shape, through hydrostatic equilibrium,[86] with an equatorial diameter of 12,756 kilometers (7,926 mi), making it the fifth-largest planetary-sized and largest terrestrial object of the Solar System,[87] and 3.7 times larger than Earth's Moon.
Chemical composition
Earth's mass is approximately 5.97×1024 kg (5.97 Rg). It is composed mostly of iron (32.1% by mass), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to gravitational separation, the core is primarily composed of the denser elements: iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.[88][48] The most common rock constituents of the crust are oxides. Over 99% of the crust is composed of various oxides of eleven elements, principally oxides containing silicon (the silicate minerals), aluminum, iron, calcium, magnesium, potassium, or sodium.[89][88]
Internal structure
 | ||
| Depth[91] (km) |
Component layer name |
Density (g/cm3) |
|---|---|---|
| 0–60 | Lithosphere[n 5] | — |
| 0–35 | Crust[n 6] | 2.2–2.9 |
| 35–660 | Upper mantle | 3.4–4.4 |
| 660–2,890 | Lower mantle | 3.4–5.6 |
| 100–700 | Asthenosphere | — |
| 2,890–5,100 | Outer core | 9.9–12.2 |
| 5,100–6,378 | Inner core | 12.8–13.1 |
Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity.[92] The thickness of the crust varies from about 6 kilometers (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid top of the upper mantle are collectively known as the lithosphere, which is divided into independently moving tectonic plates.[93]
Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low-viscosity liquid outer core lies above a solid inner core.[94] Earth's inner core may be rotating at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year, although both somewhat higher and much lower rates have also been proposed.[95] The radius of the inner core is about one-fifth of that of Earth. The density increases with depth.
Internal heat
The major contributors to Earth's internal heat are primordial heat (heat left over from Earth's formation) and radiogenic heat (heat produced by radioactive decay).[96] The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232.[97] At the center, the temperature may be up to 6,000 °C (10,830 °F),[98] and the pressure could reach 360 GPa (52 million psi).[99] Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr, twice the present-day heat would have been produced, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.[100][101]
The mean heat loss from Earth is 87 mW/m2, for a global heat loss of 4.42×1013 W.[102] A portion of the core's thermal energy is transported toward the crust by mantle plumes, a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.[103] More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans.[104]
Tectonic plates
Earth's mechanically rigid outer layer of Earth's crust and upper mantle, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundary types: at convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at