Earth

From Earthpedia


Earth
The Blue Marble, a famous photograph of Earth taken by the Apollo 17 crew in 1972
The Blue Marble, a famous photograph of Earth taken by the Apollo 17 crew in 1972
Discovery Known since prehistory
Named after Terra Mater (Roman mythology) or Gaia (Greek mythology)
Mass 5.972 × 10^24 kg
Radius 6,371 km
Surface area 510.1 million km²
Volume 1.08321 × 10^12 km³
Density 5.514 g/cm³
Rotation period 23.93 hours
Axial tilt 23.5°
Average orbit distance 149.6 million km (1 AU)
Atmosphere 78% Nitrogen, 21% Oxygen, 1% other gases


Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled 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 global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is at least somewhat humid and covered by vegetation, while large sheets of ice 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 UV-light at entry. It has a composition of primarily 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 Template:Convert, 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 nitrogen to cycle.

Earth is rounded into an ellipsoid with a circumference of about 40,000 km. It is the densest planet in the Solar System. Of the four rocky planets, it is the largest and most massive. Earth is about eight light-minutes 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 (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. Tidal locking has made the Moon always face Earth with the same side.

Earth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas and dust in the early Solar System. During the first billion years of Earth's history, the ocean formed and then life developed within it. 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.[1]

Etymology[edit]

The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled [[eorðe|]].[2] It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was used to translate the many senses of Latin [[terra|]] and Greek γῆ 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/Tellūs 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.[3]

Historically, "Earth" has been written in lowercase. Beginning with the use of Early Middle English, its definite sense as "the globe" was expressed as "the earth". By the era 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.[2] 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?"[4]

The name Terra /ˈtɛrə occasionally is used in scientific writing and especially in science fiction to distinguish humanity's inhabited planet from others,[5] while in poetry Tellus /ˈtɛləs has been used to denote personification of the Earth.[6] 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 Gæa or Gaea (English: /ˈdʒiː.ə/) of the Greek poetic name Gaia (Γαῖα; Ancient Greek: [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 /ˈgaɪ.ə rather than the more classical English /ˈgaɪ.ə.[7]

There are a number of adjectives for the planet Earth. The word "earthly" is derived from "Earth". From the Latin Terra comes terran /ˈtɛrən,[8] terrestrial /təˈrɛstriəl,[9] and (via French) terrene /tləˈriːn,[10] and from the Latin Tellus comes tellurian /tɛˈlʊəriən[11] and telluric.[12]

Natural history[edit]

Main article: History of Earth, Timeline of natural history


Formation[edit]

Further information: Hadean.

A 2012 artistic impression of the early Solar System's protoplanetary disk from which Earth and other Solar System bodies were formed

The oldest material found in the Solar System is dated to 4.5682 +0.0002 −0.0004 Ga (billion years) ago.[13] By 4.54±0.04 Ga the primordial Earth had formed.[14] 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.[15]

Estimates of the age of the Moon range from 4.5 Ga to significantly younger.[16] A 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.[17] It hit Earth with a glancing blow and some of its mass merged with Earth.[18][19] Between approximately 4.04.0 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.[20]

After formation[edit]

Main article: Geological history of Earth

Earth's atmosphere and oceans were formed by volcanic activity and outgassing.[21] Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets.[22] Sufficient water to fill the oceans may have been on Earth since it formed.[23] In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity.[24] By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.[25]

Pale orange dot, an artist's impression of Early Earth, featuring its tinted orange methane-rich early atmosphere[26]

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.[27] The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggests that at least some felsic crust existed as early as 4.4 Ga, only 140 Ma after Earth's formation.[28] There are two main models of how this initial small volume of continental crust evolved to reach its current abundance:[29] (1) a relatively steady growth up to the present day,[30] 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,[31][32] 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.[33]

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.[34]

The most recent pattern of ice ages began about 40 Ma,[35] and then intensified during the Pleistocene about 3 Ma.[36] 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.[37] 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.[38]

Origin of life and evolution[edit]

Main article: Abiogenesis, Earliest known life forms, History of life

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.[39] 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.[40] The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.[41] 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.[42] Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia,[43] biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland,[44] and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia.[45][46] The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms.[47][48]

An artist's impression of the Archean, the eon after Earth's formation, featuring round stromatolites, which are early oxygen-producing forms of life from billions of years ago. After the Late Heavy Bombardment, Earth's crust had cooled, its water-rich barren surface is marked by continents and volcanoes, with the Moon still orbiting Earth half as far as it is today, appearing 2.8 times larger and producing strong tides.[49]

During the Neoproterozoic, 1000nto 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.[50][51] Following the Cambrian explosion, 53 Ma, there have been at least five major mass extinctions and many minor ones.[52] 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 Mys, and several million years ago, an African ape species gained the ability to stand upright.[53][54] 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.[55]

Geology[edit]

Earth is composed of several layers:

  • Crust: The thin, outermost layer.
  • Mantle: A thick layer of silicate rocks.
  • Core: Divided into a liquid outer core and a solid inner core, mainly composed of iron and nickel.

Atmosphere[edit]

Earth's atmosphere is a thin layer of gases surrounding the planet. It consists primarily of:

The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, reducing temperature extremes, and acting as a medium for the water cycle.

Climate and Weather[edit]

The climate on Earth varies widely depending on geographic location, time of year, and natural phenomena. Earth has five major climate zones:

  • Tropical
  • Dry
  • Temperate
  • Cold
  • Polar

Life on Earth[edit]

Earth supports an estimated 8.7 million species of plants, animals, and microorganisms, though many remain undiscovered. Photosynthesis by plants and algae produces the oxygen that sustains most life.

Human Presence[edit]

Humans have significantly altered Earth's environment through activities such as deforestation, pollution, and the greenhouse effect. Space exploration has allowed humans to study Earth and its place in the universe.

See also[edit]

References[edit]

  1. ↑ What Is Climate Change? (en).
  2. ↑ 2.0 2.1 Oxford English Dictionary(3 ed.). Oxford University Press,2010.ISBN 978-0-19-957112-3.
  3. ↑ Dictionary of Northern Mythology. D.S. Brewer,2007.ISBN 978-0-85991-513-7.
  4. ↑ The New Oxford Dictionary of English(1st ed.). Oxford University Press,1998.ISBN 978-0-19-861263-6.
  5. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  6. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  7. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  8. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  9. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  10. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  11. ↑ Error on call to Template:cite web: Parameters url and title must be specified. Oxford University Press.
  12. ↑ Template:Cite encyclopedia
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bouvier_wadhwa2010
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named age_earth1
  15. ↑ Ag Isotopic Evolution of the Mantle During Accretion: New Constraints from Pd and Ag Metal–Silicate Partitioning. Differentiation: Building the Internal Architecture of Planets.Vol. 2084. Available at: Link.
  16. ↑ Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples. Space Science Reviews.Vol. 215(8). doi:10.1007/s11214-019-0622-x.
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named reilly20091022
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named canup_asphaug2001b
  19. ↑ On the origin and composition of Theia: Constraints from new models of the Giant Impact. Icarus.Vol. 242. doi:10.1016/j.icarus.2014.08.003.
  20. ↑ Encyclopedia of Astrobiology. Springer Berlin Heidelberg,2011.ISBN 978-3-642-11271-3.
  21. ↑ Earth's Early Atmosphere and Oceans. Lunar and Planetary Institute. Universities Space Research Association.
  22. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named watersource
  23. ↑ Earth's water may have been inherited from material similar to enstatite chondrite meteorites. Science.Vol. 369(6507). pp. 1110–1113. doi:10.1126/science.aba1948. Available at: Link.
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  26. ↑ Organic haze on Titan and the early Earth. Proceedings of the National Academy of Sciences.Vol. 103(48). pp. 18035–18042. doi:10.1073/pnas.0608561103.
  27. ↑ The composition of the Earth. Chemical Geology.Vol. 120(3–4). 1995.pp. 223–253. doi:10.1016/0009-2541(94)00140-4. Available at: Link.
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  32. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named tp322_19
  33. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Dhuime_etal_2018
  34. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bradley_2011
  35. ↑ Kinzler, Ro. "When and how did the ice age end? Could another one start?". [{{#explode:https://www.amnh.org/explore/ology/earth/ask-a-scientist-about-our-environment/how-did-the-ice-age-end%7C/%7C0}}//{{#explode:https://www.amnh.org/explore/ology/earth/ask-a-scientist-about-our-environment/how-did-the-ice-age-end%7C/%7C2}} Ology]. American Museum of Natural History (archived from the original on June 27, 2019 on Error: Invalid time.; retrieved on June 27, 2019)
  36. ↑ Causes of ice age intensification across the Mid-Pleistocene Transition. Proc Natl Acad Sci U S A.Vol. 114(50). pp. 13114–13119. doi:10.1073/pnas.1702143114.
  37. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named psc
  38. ↑ The potential of New Zealand kauri (Agathis australis) for testing the synchronicity of abrupt climate change during the Last Glacial Interval (60,000–11,700 years ago). Quaternary Science Reviews.Vol. 29(27–28). 2010.pp. 3677–3682. doi:10.1016/j.quascirev.2010.08.017. Available at: Link.
  39. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named sa282_6_90
  40. ↑ Zimmer, Carl (3 October 2013)Template:Namespace. "Earth's Oxygen: A Mystery Easy to Take for Granted". [{{#explode:https://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html%7C/%7C0}}//{{#explode:https://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html%7C/%7C2}} The New York Times] (archived from the original on October 3, 2013 on Error: Invalid time.; retrieved on October 3, 2013)
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  43. ↑ Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia. Astrobiology.Vol. 13(12). pp. 1103–1124. doi:10.1089/ast.2013.1030.
  44. ↑ Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks. Nature Geoscience.Vol. 7(1). pp. 25–28. doi:10.1038/ngeo2025.
  45. ↑ Borenstein, Seth (19 October 2015)Template:Namespace. "Hints of life on what was thought to be desolate early Earth". [{{#explode:http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html%7C/%7C0}}//{{#explode:http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html%7C/%7C2}} Excite]. Yonkers, NY: Mindspark Interactive Network. Associated Press (archived from the original on August 18, 2016 on Error: Invalid time.; retrieved on October 20, 2015)
  46. ↑ Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon. Proc. Natl. Acad. Sci. U.S.A..Vol. 112(47). pp. 14518–4521. doi:10.1073/pnas.1517557112. Early edition, published online before print.
  47. ↑ Tyrell, Kelly April (18 December 2017). Oldest fossils ever found show life on Earth began before 3.5 billion years ago. University of Wisconsin–Madison.
  48. ↑ SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions. PNAS.Vol. 115(1). 2017.pp. 53–58. doi:10.1073/pnas.1718063115.
  49. ↑ Earth-Moon Dynamics.
  50. ↑ Climate Change and the Course of Global History. Cambridge University Press,2014.ISBN 978-0-521-87164-8.
  51. ↑ Epigenetic Mechanisms of the Cambrian Explosion. Elsevier Science,2019.ISBN 978-0-12-814312-4.
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  53. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gould1994
  54. ↑ Postcranial evidence of late Miocene hominin bipedalism in Chad. Nature.Vol. 609(7925). pp. 94–100. doi:10.1038/s41586-022-04901-z. Available at: Link.
  55. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bgsa119_1_140

External links[edit]

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