Earth

Environment and Ecosystem

Earth is the only place where life is known to exist. The planet's lifeforms are sometimes said to form a "biosphere". This biosphere is generally believed to have begun evolving about 3.5 billion (3.5×109) years ago. The biosphere is divided into a number of biomes, inhabited by broadly similar flora and fauna. On land, biomes are separated primarily by latitude. Terrestrial biomes lying within the Arctic and Antarctic Circles are relatively barren of plant and animal life, while most of the more populous biomes lie near the Equator.

Related Topics:
Biosphere - Evolving - Biome - Flora - Fauna - Latitude - Arctic - Antarctic Circle - Plant - Animal - Equator

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Climate

Two large areas of polar climates separated by two rather narrow temperate zones from a wide equatorial band of tropical to subtropical climates. Precipitation patterns vary widely, ranging from several metres of water per year to less than a millimetre.

Related Topics:
Climate - Temperate - Equator - Tropical - Subtropical - Precipitation

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Ocean currents, particularly the spectacular Thermohaline circulation which distributes heat energy from the equatorial oceans to the polar regions, are important determinators of climate.

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Terrain

Elevation extremes: (measured relative to sea level)

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• Lowest point on land: Dead Sea −417 m
• Lowest point overall: Mariana Trench in the Pacific Ocean −10,924 m http://www.rain.org/ocean/ocean-studies-challenger-deep-mariana-trench.html
• Highest point: Mount Everest 8,850 m (1999 est.)

Natural resources

• Earth's crust contains large deposits of fossil fuels: (coal, petroleum, natural gas, methane clathrate). These deposits are used by humans both for energy production and as feedstock for chemical production.
• Mineral ore bodies have been formed in Earth's crust by the action of erosion and plate tectonics. These ore bodies form concentrated sources for many metals and other useful elements.
• Earth's biosphere produces many useful biological products, 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.

Some of these resources, such as mineral fuels, are difficult to replenish on a short time scale, called non-renewable resources. The exploitation of non-renewable resources by human civilization has become a subject of significant controversy in modern environmentalism movements.

Related Topics:
Mineral fuel - Non-renewable resources - Civilization - Environmentalism

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Land use

• arable land: 10%
• permanent crops: 1%
• permanent pastures: 26%
• forests and woodland: 32%
• urban areas: 1.5%
• other: 30% (1993 est.)

Irrigated land:

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2,481,250 km2 (1993 est.)

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Natural and environmental hazards

Large areas are subject to extreme weather such as (tropical cyclones), hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, floods, droughts, and other calamities and disasters.

Related Topics:
Weather - Cyclone - Hurricane - Typhoon - Earthquake - Landslide - Tsunami - Volcanic eruptions - Tornado - Sinkhole - Flood - Drought - Disaster

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Large areas are subject to overpopulation, industrial disasters such as pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species.

Related Topics:
Overpopulation - Pollution - Acid rain - Overgrazing - Deforestation - Desertification - Wildlife - Species - Extinction - Soil degradation - Erosion - Invasive species

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Long-term climate alteration due to enhancement of the greenhouse effect by human industrial carbon dioxide emissions is an increasing concern, the focus of intense study and debate.

Related Topics:
Climate - Alteration - Greenhouse effect - Carbon dioxide

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Human geography

On 25 February 2005 the United Nations Population Division issued revised estimates and projected that the world's population will reach 7 billion by 2013 and swell to 9.1 billion in 2050. Most of the growth is expected to take place in developing nations.

Related Topics:
25 February - 2005 - United Nations Population Division - 2013 - 2050 - Developing nations

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Nearly all humans currently reside on Earth: 6,411,000,000 inhabitants (January 5 2005 est.)

Related Topics:
Human - January 5 - 2005

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Two humans are presently in orbit around Earth on board the International Space Station. The station crew is replaced with new personnel every six months. During the exchange there are more, and sometimes others are also traveling briefly above the atmosphere.

Related Topics:
International Space Station - Traveling briefly above the atmosphere

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In total, about 400 people have been outside Earth (in space) as of 2004.

Related Topics:
People - 2004

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See also space colonization.

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The northernmost settlement in the world is Alert, Ellesmere Island, Canada. The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole.

Related Topics:
Alert - Ellesmere Island - Canada - Amundsen-Scott South Pole Station - Antarctica - South Pole

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There are 267 administrative divisions, including nations, dependent areas, other, and miscellaneous entries. Earth does not have a sovereign government with planet-wide authority. Independent sovereign nations claim all of the land surface except Antarctica. There is a worldwide general international organization, the United Nations. The United Nations is primarily an international discussion forum with only limited ability to pass and enforce laws.

Related Topics:
Sovereign - Government - Nations - Antarctica - International organization - United Nations - Law

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