Earth
<p ><img src="/38f289eb-5743-5ff0-90bb-25551f02595d.png"/><b>earth</b></p>
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<img src="/38f289eb-5743-5ff0-90bb-25551f02595d.png"/>earth</p>
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<b>Earth</b> (or <b>the Earth</b>) is the third <a href="http://en.wikipedia.org/wiki/Planet" title="Planet" >planet</a> from the <a href="http://en.wikipedia.org/wiki/Sun" title="Sun" >Sun</a>, and the <a href="http://en.wikipedia.org/wiki/Density" title="Density" >densest</a> and fifth-largest of the eight planets in the <a href="http://en.wikipedia.org/wiki/Solar_System" title="Solar System" >Solar System</a>. It is also the largest of the Solar System's four <a href="http://en.wikipedia.org/wiki/Terrestrial_planet" title="Terrestrial planet" >terrestrial planets</a>. It is sometimes referred to as the <a href="http://en.wikipedia.org/wiki/World" title="World" >world</a>, the Blue Planet,<sup id="cite_ref-blueplanet_25-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-blueplanet-25" >[21]</a></sup> or by its Latin name,<i><a href="http://en.wiktionary.org/wiki/Terra" class="extiw" title="wikt:Terra" >Terra</a></i>.<sup id="cite_ref-Terra_26-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-Terra-26" >[note 6]</a></sup>
Earth formed approximately <a href="http://en.wikipedia.org/wiki/Age_of_the_Earth" title="Age of the Earth" >4.54 billion years</a> ago by accretion from the <a href="http://en.wikipedia.org/wiki/Solar_nebula" title="Solar nebula" class="mw-redirect" >solar nebula</a>, and<a href="http://en.wikipedia.org/wiki/Abiogenesis" title="Abiogenesis" >life appeared</a> on its surface within one billion years.<sup id="cite_ref-age_earth1_27-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-age_earth1-27" >[22]</a></sup> The planet is home to millions of<a href="http://en.wikipedia.org/wiki/Species" title="Species" >species</a>, including <a href="http://en.wikipedia.org/wiki/Humans" title="Humans" class="mw-redirect" >humans</a>.<sup id="cite_ref-science_241_4872_1441_28-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-science_241_4872_1441-28" >[23]</a></sup> Earth's <a href="http://en.wikipedia.org/wiki/Biosphere" title="Biosphere" >biosphere</a> has significantly altered <a href="http://en.wikipedia.org/wiki/Earth%27s_atmosphere" title="Earth's atmosphere" class="mw-redirect" >the atmosphere</a>and other <a href="http://en.wikipedia.org/wiki/Abiotic" title="Abiotic" class="mw-redirect" >abiotic</a> conditions on the planet, enabling the proliferation of <a href="http://en.wikipedia.org/wiki/Aerobic_organism" title="Aerobic organism" >aerobic organisms</a>as well as the formation of the <a href="http://en.wikipedia.org/wiki/Ozone_layer" title="Ozone layer" >ozone layer</a> which, together with <a href="http://en.wikipedia.org/wiki/Earth%27s_magnetic_field" title="Earth's magnetic field" >Earth's magnetic field</a>, blocks harmful solar radiation, permitting life on land.<sup id="cite_ref-Harrison_2002_29-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-Harrison_2002-29" >[24]</a></sup> The <a href="http://en.wikipedia.org/wiki/Geophysics" title="Geophysics" >physical properties of the Earth</a>, as well as its <a href="http://en.wikipedia.org/wiki/Geological" title="Geological" class="mw-redirect" >geological</a> history and orbit, have allowed life to persist. The planet is expected to continue supporting life for another 500 million to 2.3 billion years.<sup id="cite_ref-britt2000_30-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-britt2000-30" >[25]</a></sup><sup id="cite_ref-carrington_31-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-carrington-31" >[26]</a></sup><sup id="cite_ref-pnas1_24_9576_32-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-pnas1_24_9576-32" >[27]</a></sup>
Earth's <a href="http://en.wikipedia.org/wiki/Crust(geology)" title="Crust (geology)" >crust</a> is divided into several rigid segments, or <a href="http://en.wikipedia.org/wiki/Tectonic_plate" title="Tectonic plate" class="mw-redirect" >tectonic plates</a>, that migrate across the surface over periods of <a href="http://en.wikipedia.org/wiki/Geologic_time_scale" title="Geologic time scale" >many millions of years</a>. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the <a href="http://en.wikipedia.org/wiki/Hydrosphere" title="Hydrosphere" >hydrosphere</a>. Earth's<a href="http://en.wikipedia.org/wiki/Geographical_pole" title="Geographical pole" >poles</a> are mostly covered with solid ice (<a href="http://en.wikipedia.org/wiki/Antarctic_ice_sheet" title="Antarctic ice sheet" >Antarctic ice sheet</a>) or <a href="http://en.wikipedia.org/wiki/Sea_ice" title="Sea ice" >sea ice</a> (<a href="http://en.wikipedia.org/wiki/Arctic_ice_cap" title="Arctic ice cap" class="mw-redirect" >Arctic ice cap</a>). <a href="http://en.wikipedia.org/wiki/Structure_of_the_Earth" title="Structure of the Earth" >The planet's interior</a> remains active, with a thick layer of relatively solid <a href="http://en.wikipedia.org/wiki/Mantle(geology)" title="Mantle (geology)" >mantle</a>, a liquid <a href="http://en.wikipedia.org/wiki/Outer_core" title="Outer core" >outer core</a>that generates a magnetic field, and a solid iron <a href="http://en.wikipedia.org/wiki/Inner_core" title="Inner core" >inner core</a>.
Earth interacts with other objects in space, especially the Sun and the <a href="http://en.wikipedia.org/wiki/Moon" title="Moon" >Moon</a>. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 <a href="http://en.wikipedia.org/wiki/Solar_day" title="Solar day" class="mw-redirect" >solar days</a>, or one <a href="http://en.wikipedia.org/wiki/Sidereal_year" title="Sidereal year" >sidereal year</a>.<sup id="cite_ref-sidereal_solar_33-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-sidereal_solar-33" >[note 7]</a></sup> The Earth's axis of rotation is <a href="http://en.wikipedia.org/wiki/Axial_tilt" title="Axial tilt" >tilted</a> 23.4° away from the <a href="http://en.wikipedia.org/wiki/Perpendicular" title="Perpendicular" >perpendicular</a> of its <a href="http://en.wikipedia.org/wiki/Orbital_plane_(astronomy)" title="Orbital plane (astronomy)" >orbital plane</a>, producing seasonal variations on the planet's surface with a period of one <a href="http://en.wikipedia.org/wiki/Tropical_year" title="Tropical year" >tropical year</a> (365.24 solar days).<sup id="cite_ref-yoder1995_34-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-yoder1995-34" >[28]</a></sup> Earth's only known<a href="http://en.wikipedia.org/wiki/Natural_satellite" title="Natural satellite" >natural satellite</a>, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean <a href="http://en.wikipedia.org/wiki/Tides" title="Tides" class="mw-redirect" >tides</a>, stabilizes the axial tilt, and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous <a href="http://en.wikipedia.org/wiki/Asteroid" title="Asteroid" >asteroid</a> impacts during the<a href="http://en.wikipedia.org/wiki/Late_Heavy_Bombardment" title="Late Heavy Bombardment" >Late Heavy Bombardment</a> caused significant changes to the greater surface environment.
Both the <a href="http://en.wikipedia.org/wiki/Mineral" title="Mineral" >mineral</a> resources of the planet and the products of the <a href="http://en.wikipedia.org/wiki/Biosphere" title="Biosphere" >biosphere</a> contribute resources that are used to support a <a href="http://en.wikipedia.org/wiki/World_population" title="World population" >global human population</a>.<sup id="cite_ref-World_Population_Clock_35-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Earth#cite_note-World_Population_Clock-35" >[29]</a></sup> These inhabitants are grouped into about 200 independent <a href="http://en.wikipedia.org/wiki/Sovereign_state" title="Sovereign state" >sovereign states</a> (193 United Nations recognized sovereign states), which interact through diplomacy, travel, trade, and military action. <a href="http://en.wikipedia.org/wiki/Human_culture" title="Human culture" class="mw-redirect" >Human cultures</a> have developed many views of the planet, including <a href="http://en.wikipedia.org/wiki/Personification" title="Personification" class="mw-redirect" >personification</a> as a <a href="http://en.wikipedia.org/wiki/Deity" title="Deity" >deity</a>, a belief in a <a href="http://en.wikipedia.org/wiki/Flat_Earth" title="Flat Earth" >flat Earth</a> or in the <a href="http://en.wikipedia.org/wiki/Geocentric_model" title="Geocentric model" >Earth as the center of the universe</a>, and a modern perspective of the world as an <a href="http://en.wikipedia.org/wiki/Gaia_hypothesis" title="Gaia hypothesis" >integrated environment</a> that requires stewardship.</p>