Earth

Earth
Earth  is the third   planet  from the   Sun, and the   densest  and fifth-largest of the eight planets in the   Solar System. It is also the largest of the Solar System's four   terrestrial planets. It is sometimes referred to as the   world, the Blue Planet, <sup class="reference" id="cite_ref-blueplanet_27-0" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[22] <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">or by its Latin name, <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Terra<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">. <sup class="reference" id="cite_ref-Terra_28-0" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[note 6]

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">Earth formed approximately 4.54 billion years ago, and life appeared on its surface within one billion years.<sup class="reference" id="cite_ref-age_earth1_29-0" style="line-height:1em;">[23]  Earth's biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of the ozone layer, which together with Earth's magnetic field blocked harmful solar radiation, and permitted formerly ocean-confined life to move safely to land.<sup class="reference" id="cite_ref-Harrison_2002_30-0" style="line-height:1em;">[24]  The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. Estimates on how much longer the planet will be able to continue to support life range from  500 million years (myr), to as long as  2.3 billion years (byr) .<sup class="reference" id="cite_ref-britt2000_31-0" style="line-height:1em;">[25

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;"><sup class="reference" id="cite_ref-britt2000_31-0" style="line-height:1em;">] <sup class="reference" id="cite_ref-carrington_32-0" style="line-height:1em;">[26] <sup class="reference" id="cite_ref-pnas1_24_9576_33-0" style="line-height:1em;">[27]

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">Earth's lithosphere is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. 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 hydrosphere. Earth's poles are mostly covered with ice that is the solid ice of the Antarctic ice sheet and the sea icethat is the polar ice packs. The planet's interior remains active, with a solid iron inner core, a liquid outer core that generates the magnetic field, and a thick layer of relatively solid mantle.

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the sun, the Earth rotates about its own axis 366.26 times, creating 365.26 solar days, or one sidereal year.<sup class="reference" id="cite_ref-sidereal_solar_34-0" style="line-height:1em;">[note 7]  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).<sup class="reference" id="cite_ref-yoder1995_35-0" style="line-height:1em;">[28]  The Moon is Earth's only natural satellite. It began orbiting the Earth about  4.53 billion years ago (bya). The Moon's gravitational interaction with Earth stimulates ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation.

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">The planet is home to millions of species, including humans.<sup class="reference" id="cite_ref-science_241_4872_1441_36-0" style="line-height:1em;">[29]  Both the mineral resources of the planet and the products of the biosphere contribute resources that are used to support a global human population.<sup class="reference" id="cite_ref-World_Population_Clock_37-0" style="line-height:1em;">[30]  These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including its personification as a planetarydeity, its shape as flat, its position as the center of the universe, and in the modern Gaia Principle, as a single, self-regulating organism in its own right.