These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment.īoth the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population. Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. The Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 solar days, or one sidereal year. The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.Įarth interacts with other objects in space, especially the Sun and the Moon. Earth's poles are mostly covered with solid ice ( Antarctic ice sheet) or sea ice ( Arctic ice cap). Liquid water, necessary for all known life, is not known to exist in equilibrium on any other planet's surface. About 71% of the surface is covered with salt water oceans, the remainder consisting of continents and islands which together have many lakes and other sources of water contributing to the hydrosphere. The planet is expected to continue supporting life for at least another 500 million years.Įarth's outer surface is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The planet formed 4.54 billion years ago, and life appeared on its surface within one billion years. It is sometimes referred to as the World, the Blue Planet,or by its Latin name, Terra.Įarth is home to millions of species including humans. It is also the largest of the Solar System's four terrestrial planets. Earth (or the Earth) is the third planet (or rock) from the Sun and the densest and fifth-largest of the eight planets in the Solar System.
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