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Land, sometimes referred to as dry land, is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity occurs in land areas that support agriculture, habitat, and various natural resources.
Areas where land meets large bodies of water are called coastal zones. The division between land and water is a fundamental concept to humans, which can have strong cultural importance. The demarcation between land and water varies by local jurisdiction. A Maritime boundary is one such political demarcation. A variety of natural boundaries exist to help define where water meets land. Solid rock landforms are easier to demarcate than marshy or swampy boundaries, where there is no clear point at which the land ends and a body of water has begun. Demarcation can further vary due to tides and weather.
Etymology and terminology
The word 'land' derives from Middle English land, lond and Old English land, lond (“earth, land, soil, ground; defined piece of land, territory, realm, province, district; landed property; country (not town); ridge in a ploughed field”), from Proto-Germanic *landą (“land”), and from Proto-Indo-European *lendʰ- (“land, heath”). Cognate with Scots land (“land”), West Frisian lân (“land”), Dutch land (“land”), German Land (“land, country, state”), Swedish land (“land, country, shore, territory”), Icelandic land (“land”). Non-Germanic cognates include Old Irish lann (“heath”), Welsh llan (“enclosure”), Breton lann (“heath”), Old Church Slavonic lędо from Proto-Slavic *lenda (“heath, wasteland”) and Albanian lëndinë (“heath, grassland”) from lëndë (“matter, substance”).
A continuous area of land surrounded by ocean is called a landmass. Although it may be most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it is also used as two words. Landmasses include supercontinents, continents, and islands. There are four major continuous landmasses of the Earth: Afro-Eurasia, Americas, Australia and Antarctica.
History of land on Earth
The earliest material found in the Solar System is dated to 4.5672±0.0006 bya (billion years ago); therefore, the Earth itself must have been formed by accretion around this time. By 4.54±0.04 bya, the primordial Earth had formed. The formation and evolution of the Solar System bodies occurred in tandem 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 in tandem with the star. A nebula contains gas, ice grains and dust (including primordial nuclides). In nebular theory planetesimals commence forming as particulate accrues by cohesive clumping and then by gravity. The assembly of the primordial Earth proceeded for 10–20 myr.
Earth's atmosphere and oceans formed by volcanic activity and outgassing that included water vapor. The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, proto-planets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing while the newly forming Sun was only at 70% luminosity. By 3.5 bya, the Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.
The crust, parts of which currently form the Earth's land, formed when the molten outer layer of the planet Earth cooled to form a solid as the accumulated water vapor began to act in the atmosphere. The two models that explain land mass propose either a steady growth to the present-day forms or, more likely, a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from the earth's interior. On time scales lasting hundreds of millions of years, the supercontinents have formed and broken up three times. Roughly 750 mya (million years ago), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which also broke apart 180 mya.
Land mass refers to the total surface area of the land of a geographical region or country (which may include discontinuous pieces of land such as islands). It is written as two words to distinguish it from the usage "landmass" —the contiguous area of land surrounded by ocean.
The Earth's total land mass is 148,939,063.133 km2 (57,505,693.767 sq mi) which is about 29.2% of its total surface. Water covers approximately 70.8% of the Earth's surface, mostly in the form of oceans.
Creation myths in many religions recall a story involving the creation of the world by a supernatural deity or deities, including accounts wherein the land is separated from the oceans and the air. The Earth itself has often been personified as a deity, in particular a goddess. In many cultures the mother goddess is also portrayed as a fertility deity. To the Aztecs, Earth was called Tonantzin—"our mother"; to the Incas, Earth was called Pachamama—"mother earth". The Chinese Earth goddess Hou Tu is similar to Gaia, the Greek goddess personifying the Earth. Bhuma Devi is the Goddess of Earth in Hinduism, influenced by Graha. In Norse mythology, the Earth giantess Jörð was the mother of Thor and the daughter of Annar. Ancient Egyptian mythology is different from that of other cultures because Earth (Geb) is male and sky (Nut) is female.
In early Egyptian and Mesopotamian thought the world was portrayed as a flat disk floating in the ocean. The Egyptian universe was pictured as a rectangular box with a north-south orientation and with a slightly concave surface, with Egypt in the center. A similar model is found in the Homeric account of the 8th century BC in which "Okeanos, the personified body of water surrounding the circular surface of the Earth, is the begetter of all life and possibly of all gods." The biblical earth is a flat disc floating on water.
The Pyramid Texts and Coffin Texts reveal that the ancient Egyptians believed Nun (the Ocean) was a circular body surrounding nbwt (a term meaning "dry lands" or "Islands"), and therefore believed in a similar Ancient Near Eastern circular earth cosmography surrounded by water.
The spherical form of the Earth was suggested by early Greek philosophers; a belief espoused by Pythagoras. Contrary to popular belief, most people in the Middle Ages did not believe the Earth was flat: this misconception is often called the "Myth of the Flat Earth". As evidenced by thinkers such as Thomas Aquinas, European belief in a spherical Earth was widespread by this point in time. Prior to circumnavigation of the planet and the introduction of space flight, belief in a spherical Earth was based on observations of the secondary effects of the Earth's shape and parallels drawn with the shape of other planets.
Most planets and satellites known to man are either gaseous or solid. The gas giants Jupiter and Saturn are thought to lack solid surface layers and instead have a stratum of liquid hydrogen; however, their planetary geology is not well understood. The possibility of Uranus and Neptune possessing hot, highly compressed, supercritical water under their thick atmospheres has been hypothesised. While their composition is still not fully understood, a 2006 study by Wiktorowicz et al. ruled out the possibility of such an water "ocean" existing on Neptune, though some studies have suggested that exotic oceans of liquid diamond are possible. The entire surface of a rocky planet or moon is considered land, even though there is no sea to contrast it against.
- The picture of the universe in Talmudic texts has the Earth in the center of creation with heaven as a hemisphere spread over it. Biblical writings, such as the Genesis creation story and the various Psalms that extol the firmament, the stars, the sun, and the earth, give similar explanations. The Hebrews saw the earth as an almost flat surface consisting of a solid and a liquid part and the sky as the realm of light in which heavenly bodies move. The earth rested on cornerstones and could not be moved except by Jehovah (as in an earthquake). According to the Hebrews, the sun and the moon were only a short distance from one another. "Cosmology." Encyclopedia Americana. Grolier Online, 2012. Author: Giorgio Abetti, Astrophysical Observatory of Arcetri-Firenze.
- The Earth is usually described as a disk encircled by water. Cosmological and metaphysical speculations were not to be cultivated in public nor were they to be committed to writing. Rather, they were considered to be "secrets of the Torah not to be passed on to all and sundry" (Ketubot 112a). While study of God's creation was not prohibited, speculations about "what is above, what is beneath, what is before, and what is after" (Mishnah Hagigah: 2) were restricted to the intellectual elite. (Topic Overview: Judaism, Encyclopedia of Science and Religion, Ed. J. Wentzel Vrede van Huyssteen. Vol. 2. New York: Macmillan Reference USA, 2003. p477-483. Hava Tirosh-Samuelson).
- Michael Allaby, Chris Park, A Dictionary of Environment and Conservation (2013), page 239, ISBN 0199641668.
- Bowring, S.; Housh, T. (1995). "The Earth's early evolution". Science 269 (5230): 1535–40. Bibcode:1995Sci...269.1535B. doi:10.1126/science.7667634. PMID 7667634.
- Dalrymple, G.B. (1991). The Age of the Earth. California: Stanford University Press. ISBN 0-8047-1569-6.
- Newman, William L. (2007-07-09). "Age of the Earth". Publications Services, USGS. Retrieved 2007-09-20.
- Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Geological Society, London, Special Publications 190 (1): 205–221. Bibcode:2001GSLSP.190..205D. doi:10.1144/GSL.SP.2001.190.01.14. Retrieved 2007-09-20.
- Stassen, Chris (2005-09-10). "The Age of the Earth". TalkOrigins Archive. Retrieved 2008-12-30.
- Yin, Qingzhu; Jacobsen, S. B.; Yamashita, K.; Blichert-Toft, J.; Télouk, P.; Albarède, F. (2002). "A short timescale for terrestrial planet formation from Hf-W chronometry of meteorites". Nature 418 (6901): 949–952. Bibcode:2002Natur.418..949Y. doi:10.1038/nature00995. PMID 12198540.
- Morbidelli, A. et al. (2000). "Source regions and time scales for the delivery of water to Earth". Meteoritics & Planetary Science 35 (6): 1309–1320. Bibcode:2000M&PS...35.1309M. doi:10.1111/j.1945-5100.2000.tb01518.x.
- Guinan, E. F.; Ribas, I. "Our Changing Sun: The Role of Solar Nuclear Evolution and Magnetic Activity on Earth's Atmosphere and Climate". In Benjamin Montesinos, Alvaro Gimenez and Edward F. Guinan. ASP Conference Proceedings: The Evolving Sun and its Influence on Planetary Environments. San Francisco: Astronomical Society of the Pacific. Bibcode:2002ASPC..269...85G. ISBN 1-58381-109-5.
- Staff (March 4, 2010). "Oldest measurement of Earth's magnetic field reveals battle between Sun and Earth for our atmosphere". Physorg.news. Retrieved 2010-03-27.
- Rogers, John James William; Santosh, M. (2004). Continents and Supercontinents. Oxford University Press US. p. 48. ISBN 0-19-516589-6.
- Hurley, P. M.; Rand, J. R. (Jun 1969). "Pre-drift continental nuclei". Science 164 (3885): 1229–1242. Bibcode:1969Sci...164.1229H. doi:10.1126/science.164.3885.1229. PMID 17772560.
- De Smet, J.; Van Den Berg, A.P.; Vlaar, N.J. (2000). "Early formation and long-term stability of continents resulting from decompression melting in a convecting mantle". Tectonophysics 322 (1–2): 19. Bibcode:2000Tectp.322...19D. doi:10.1016/S0040-1951(00)00055-X.
- Armstrong, R. L. (1968). "A model for the evolution of strontium and lead isotopes in a dynamic earth". Reviews of Geophysics 6 (2): 175–199. Bibcode:1968RvGSP...6..175A. doi:10.1029/RG006i002p00175.
- Kleine, Thorsten; Palme, Herbert; Mezger, Klaus; Halliday, Alex N. (2005-11-24). "Hf-W Chronometry of Lunar Metals and the Age and Early Differentiation of the Moon". Science 310 (5754): 1671–1674. Bibcode:2005Sci...310.1671K. doi:10.1126/science.1118842. PMID 16308422.
- Hong, D.; Zhang, Jisheng; Wang, Tao; Wang, Shiguang; Xie, Xilin (2004). "Continental crustal growth and the supercontinental cycle: evidence from the Central Asian Orogenic Belt". Journal of Asian Earth Sciences 23 (5): 799. Bibcode:2004JAESc..23..799H. doi:10.1016/S1367-9120(03)00134-2.
- Armstrong, R. L. (1991). "The persistent myth of crustal growth". Australian Journal of Earth Sciences 38 (5): 613–630. Bibcode:1991AuJES..38..613A. doi:10.1080/08120099108727995.
- Murphy, J. B.; Nance, R. D. (1965). "How do supercontinents assemble?". American Scientist 92 (4): 324–33. doi:10.1511/2004.4.324. Retrieved 2007-03-05.
- Werner, E. T. C. (1922). Myths & Legends of China. New York: George G. Harrap & Co. Ltd. Retrieved 2007-03-14.
- H. and H. A. Frankfort, J. A. Wilson, and T. Jacobsen, Before Philosophy (Baltimore: Penguin, 1949) 54.
- Anthony Gottlieb (2000). The Dream of Reason. Penguin. p. 6. ISBN 0-393-04951-5.
- Berlin, Adele (2011). "Cosmology and creation". In Berlin, Adele; Grossman, Maxine. The Oxford Dictionary of the Jewish Religion. Oxford University Press.
- Pyramid Texts, Utterance 366, 629a-629c: "Behold, thou art great and round like the Great Round; Behold, thou are bent around, and art round like the Circle which encircles the nbwt; Behold, thou art round and great like the Great Circle which sets."(Faulkner 1969, 120)
- Ancient Near Eastern Texts, Pritchard, 1969, p.374.
- Coffin Texts, Spell 714.
- Russell, Jeffrey B. "The Myth of the Flat Earth". American Scientific Affiliation. Retrieved 2007-03-14.; but see also Cosmas Indicopleustes
- Jacobs, James Q. (1998-02-01). "Archaeogeodesy, a Key to Prehistory". Retrieved 2007-04-21.
- Wiktorowicz, Sloane J.; Ingersoll, Andrew P. (2007). "Liquid water oceans in ice giants". Icarus 186 (2): 436–447. arXiv:astro-ph/0609723. Bibcode:2007Icar..186..436W. doi:10.1016/j.icarus.2006.09.003. ISSN 0019-1035.
- Silvera, Isaac (2010). "Diamond: Molten under pressure". Nature Physics 6 (1): 9–10. Bibcode:2010NatPh...6....9S. doi:10.1038/nphys1491. ISSN 1745-2473.
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