Earth, Surface

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Summary

Earth, also known as the world, Terra, or Gaia, is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only celestial body known to accommodate life. It is home to millions of species, including billions of humans who depend upon its biosphere and minerals. The Earth's human population is divided among about two hundred independent states that interact through diplomacy, conflict, travel, trade, and media.

Details

The Earth's terrain varies greatly from place to place. About 70.8% of the surface is covered by water, with much of the continental shelf below sea level. This equates to (139.43 million sq mi). The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes, oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. The remaining 29.2% (, or 57.51 million sq mi) not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies.

The planetary surface undergoes reshaping over geological time periods due to tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects. Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts also act to reshape the landscape.

The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors. Sedimentary rock is formed from the accumulation of sediment that becomes compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form only about 5% of the crust. The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include quartz, the feldspars, amphibole, mica, pyroxene and olivine. Common carbonate minerals include calcite (found in limestone) and dolomite.

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. Currently the total arable land is 13.31% of the land surface, with only 4.71% supporting permanent crops. Close to 40% of the Earth's land surface is presently used for cropland and pasture, or an estimated 1.3 km2 of cropland and 3.4 km2 of pastureland.

The elevation of the land surface of the Earth varies from the low point of −418 m at the Dead Sea, to a 2005-estimated maximum altitude of 8,848 m at the top of Mount Everest. The mean height of land above sea level is 840 m.

Besides being divided logically into Northern and Southern Hemispheres centered on the earths poles, the earth has been divided arbitrarily into Eastern and Western Hemispheres. The surface of the Earth is traditionally divided into seven continents and various seas. As people settled and organized the planet, nearly all the land was divided into nations. As of 2013, there are about 196 recognized nations. An example of how major geographical regions can be broken down is Africa, America, Antarctica, Asia, Australia, and Europe.

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External Links

  • WikipediaEarth – ProfileEarth – Temperature and Precipitation ExtremesEarth – Climate Changes Cause Shape to Change

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