Earth
The Earth formed there are about 4.54 billion years and life appeared less than a billion years later. The planet is home to millions of living species, including humans. The biosphere of the Earth has greatly altered the atmosphere and other abiotic characteristics of the planet, enabling the proliferation of aerobic organisms as well as the formation of ozone, which associated with the Earth's magnetic field, blocks part solar radiation, enabling life on Earth. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period and the Earth should be able to sustain life (as we know it) for at least another 500 million years.
The Earth's crust is divided into several rigid segments called tectonic plates that move over millions of years. Approximately 71% of the land surface is covered by salt water oceans that form the hydrosphere with other water sources such as lakes, rivers or aquifers. The geographic poles of the Earth are mostly covered with ice (Antarctic ice sheet) or floes. The interior of the planet remains active with a thick mantle composed of silicate rocks (usually solid, but locally melted), a liquid outer core of iron that generates a magnetic field, and an inner core of solid iron.
Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun in 365.26 solar days, or a year sidéraleNote 1. The rotation axis of the Earth is tilted by 23.44 ° from perpendicular to the plane of the ecliptic, which produces seasonal variations on the surface of the planet with a period of one tropical year (365.2422 solar days). The only known natural satellite of the Earth's moon orbiter that began some 4.5 billion years. This causes the tides, stabilizes the axial tilt and slowly slows the Earth's rotation. There are about 3.8 billion years ago, during the Late Heavy Bombardment, numerous asteroid impacts caused significant changes then its surface.
Earth has the distinction, from the perspective of the human being, being the only place in the universe to harbor life as we know it, such as wildlife (including among others the human species) and flora. Human cultures have developed many representations of the planet, including personification as a deity, a belief in a flat earth, the Earth as the center of the universe and the modern perspective of the world as a global system requiring reasonable management.
The science that studies the Earth's geology. Given the influence of life on the composition of the atmosphere, oceans and sedimentary rocks, geology borrows from biology part of its chronology and its vocabulary.
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