A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain metabolism.[161] The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the current climatic conditions at the surface.[162]
Biosphere
Main article: Biosphere
A planet's life forms are sometimes said to form a "biosphere". The Earth's biosphere is generally believed to have begun evolving about 3.5 bya. The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land, biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes.[163]
Natural resources and land use
Main articles: Natural resource and Land use
Estimated human land use, 2000[164]
Land use Mha
Cropland 1,510–1,611
Pastures 2,500–3,410
Natural forests 3,143–3,871
Planted forests 126–215
Urban areas 66–351
Unused, productive land 356–445
The Earth provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale.
Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed in Earth's crust through a process of Ore genesis, resulting from actions of erosion and plate tectonics.[165] These bodies form concentrated sources for many metals and other useful elements.
The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.[166] In 1980, 5,053 Mha of the Earth's land surface consisted of forest and woodlands, 6,788 Mha were grasslands and pasture, and 1,501 Mha was cultivated as croplands.[167] The estimated amount of irrigated land in 1993 was 2,481,250 square kilometres (958,020 sq mi).[14] Humans also live on the land by using building materials to construct shelters.
Natural and environmenta
Biosphere
Main article: Biosphere
A planet's life forms are sometimes said to form a "biosphere". The Earth's biosphere is generally believed to have begun evolving about 3.5 bya. The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land, biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes.[163]
Natural resources and land use
Main articles: Natural resource and Land use
Estimated human land use, 2000[164]
Land use Mha
Cropland 1,510–1,611
Pastures 2,500–3,410
Natural forests 3,143–3,871
Planted forests 126–215
Urban areas 66–351
Unused, productive land 356–445
The Earth provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale.
Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed in Earth's crust through a process of Ore genesis, resulting from actions of erosion and plate tectonics.[165] These bodies form concentrated sources for many metals and other useful elements.
The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.[166] In 1980, 5,053 Mha of the Earth's land surface consisted of forest and woodlands, 6,788 Mha were grasslands and pasture, and 1,501 Mha was cultivated as croplands.[167] The estimated amount of irrigated land in 1993 was 2,481,250 square kilometres (958,020 sq mi).[14] Humans also live on the land by using building materials to construct shelters.
Natural and environmenta
