User:Jigme dorjee/TWA/Earth





Earth: The Earth is the third planet from the Sun. It is one of the fore terrestrial planets in our Solar System. This means most of its mass is solid. The other tree are Mercury, Mars, and Venus. The Earth is also called the Blue Planet, Planet Earth, and Terra.

The Earth is home to millions of species of plants and animals, including humans. Earth's atmosphere and oceans formed by volcanic activity and out-gassing that included water vapor. The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, proton-planets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. 



Earth: Earth (otherwise known as the world,[n 5] in Greek: Γαῖα Gaia,[n 6] or in Latin: Terra[26]) is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago.[27][28][29] Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 solar days or one sidereal year.[n 7] 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 within a period of one tropical year (365.24 solar days).[30] The Moon, Earth's only permanent natural satellite, by its gravitational relationship with Earth, causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.[31] Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. 71% of Earth's surface is covered with water.[32] The remaining 29% is land mass—consisting of continents and islands—that together has many lakes, rivers, and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, and a convecting mantle that drives plate tectonics. Within its first billion years,[33] life appeared in Earth's oceans, and began to affect the atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and today thrive. The earliest undisputed life on Earth arose at least 3.5 billion years ago. Earlier physical evidence of life includes biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland, as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia.[34][35] Except when interrupted by mass extinction events, Earth's biodiversity has continually expanded.[36] Although scholars estimate that over 99% of all species of life (over five billion)[37] that ever lived on Earth are today extinct,[38][39] there are an estimated 10–14 million species still in existence,[40][41] of which about 1.2 million have been documented and over 86% have not yet been described.[42] More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[43] Over 7.3 billion humans[44] live on Earth and depend on its biosphere and minerals for their survival. Earth's human population is divided among about 200 sovereign states that interact through diplomacy, conflict, travel, trade, and communication media. 



Formation:

Artist's impression of the early Solar System's planetary disk The earliest material found in the Solar System is dated to 4.5672±0.0006 billion years ago (Gya).[57] By 4.54±0.04 Gya[33] the primordial Earth had formed. The formation and evolution of the Solar System bodies occurred along with those of the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk along with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). In nebular theory, planetesimals form by accretion. The assembly of the primordial Earth proceeded for 10–20 Ma.[58] The process that led to the formation of the Moon approximately 4.53 billion years ago[59] is the subject of ongoing research. The working hypothesis is that it formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, impacted Earth.[60] In this scenario, the mass of Theia was approximately 10% of that of Earth,[61] it impacted Earth with a glancing blow,[62] and some of its mass merged with Earth. Between approximately 4.1 and 3.8 Gya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon, and by inference, to that of Earth.