The International Space Station is an artificial satellite that orbits Earth.
As of 2011, there are 931 operational, man-made satellites orbiting the Earth.[160] There are also inoperative satellites and over 300,000 pieces of space debris. Earth's largest artificial satellite is the International Space Station.
Habitability
See also: Planetary habitability
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
| 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 |
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 environmental hazards
Large areas of the Earth's surface are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. From 1980 to 2000, these events caused an average of 11,800 deaths per year.[168] Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, wildfires, and other calamities and disasters.Many localized areas are subject to human-made 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.
According to the United Nations, a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.[169]
Human geography
Main articles: Human geography and World
The 7 continents of Earth:[170] North America, South America, Antarctica, Africa, Europe, Asia, Australia
The Earth at night in 2000, a composite of DMSP/OLS ground illumination data on a simulated night-time image of the world
Earth has reached approximately seven billion human inhabitants as of October 31, 2011.[171] Projections indicate that the world's human population will reach 9.2 billion in 2050.[172] Most of the growth is expected to take place in developing nations. Human population density varies widely around the world, but a majority live in Asia. By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas.[173]
It is estimated that only one-eighth of the surface of the Earth is suitable for humans to live on—three-quarters is covered by oceans, and half of the land area is either desert (14%),[174] high mountains (27%),[175] or other less suitable terrain. The northernmost permanent settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada.[176] (82°28′N) The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole. (90°S)
Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica and the odd unclaimed area of Bir Tawil between Egypt and Sudan. As of 2013, there are 206 sovereign states, including the 193 United Nations member states. In addition, there are 59 dependent territories, and a number of autonomous areas, territories under dispute and other entities.[14] Historically, Earth has never had a sovereign government with authority over the entire globe, although a number of nation-states have striven for world domination and failed.[177]
The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict.[178] The U.N. serves primarily as a forum for international diplomacy and international law. When the consensus of the membership permits, it provides a mechanism for armed intervention.[179]
The first human to orbit the Earth was Yuri Gagarin on April 12, 1961.[180] In total, about 487 people have visited outer space and reached Earth orbit as of July 30, 2010, and, of these, twelve have walked on the Moon.[181][182][183] Normally the only humans in space are those on the International Space Station. The station's crew, currently six people, is usually replaced every six months.[184] The furthest humans have travelled from Earth is 400,171 km, achieved during the 1970 Apollo 13 mission.[185]
Cultural and historical viewpoint
Main article: Earth in culture
The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle.[186]Unlike the rest of the planets in the Solar System, humankind did not begin to view the Earth as a moving object in orbit around the Sun until the 16th century.[187] Earth has often been personified as a deity, in particular a goddess. In many cultures a mother goddess is also portrayed as a fertility deity. Creation myths in many religions recall a story involving the creation of the Earth by a supernatural deity or deities. A variety of religious groups, often associated with fundamentalist branches of Protestantism[188] or Islam,[189] assert that their interpretations of these creation myths in sacred texts are literal truth and should be considered alongside or replace conventional scientific accounts of the formation of the Earth and the origin and development of life.[190] Such assertions are opposed by the scientific community[191][192] and by other religious groups.[193][194][195] A prominent example is the creation–evolution controversy.
In the past, there were varying levels of belief in a flat Earth,[196] but this was displaced by spherical Earth, a concept that has been credited to Pythagoras (6th century BC).[197]
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