Land, sometimes referred to as dry land, is the solid surface of the Earth, that is not covered by water. The division between land and ocean, sea, or other bodies of water, is one of the most fundamental separations on the planet. The vast majority of human activity has historically occurred, and continues to occur, on land. For this reason, land, and particularly those areas of land that support agriculture, hunting, and other human activities, may be invested with great emotional and cultural value. Furthermore, the life forms that exist primarily on land, including terrestrial plants and terrestrial animals, differ from those that exist primarily in large bodies of water. The demarcation between land and water varies. In some places, it is sharply defined by solid rock landforms coming directly to the edge of the water. In other places, land may slowly give way to marshes or swamps, with no clear point at which the land ends and a body of water has begun. In such places, the demarcation can further vary due to tides and weather, with the area where land and sea interact being called the "coastal zone".
Etymology and terminology
The word, land, derives from Middle English land, lond, from 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”), 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”).
The visible features of an area of land are called a landscape. These include the physical elements of landforms such as (ice-capped) mountains, hills, water bodies such as rivers, lakes, ponds and the sea, living elements of land cover including indigenous vegetation, human elements including different forms of land use, buildings and structures, and transitory elements such as lighting and weather conditions.
A contiguous 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; therefore, it is inferred that 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 Aztec, 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. To Hindus it is called Bhuma Devi, the Goddess of Earth. (See also 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 is male, Geb, and sky is female, Nut.
In early Egyptian and Mesopotamian thought the world was portrayed as a flat disk floating in the ocean. 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. By the Middle Ages—as evidenced by thinkers such as Thomas Aquinas—European belief in a spherical Earth was widespread. 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 surfaces 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 land, even though there is no sea to contrast it against.
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