Earth 98

Earth is the third planet from the sun and is the only known planetary body capable of harboring life. Earth formed around four billion years ago out of the accretion disk of the sun, becoming a body about 1.3-1.5 times its current size. Roughly 3.5 billion years ago, early in its planetary history, earth suffered a catastrophic impact event with a planet weighing about 1/4 of its mass. This massive impact destroyed the other body, temporarily creating a huge ring system around earth and causing millions of years of meteor activity. Eventually the rings coalesced into the planet's only moon. The moon and the large outer gas giants, now that the "spare" planets of the accretion disk had been destroyed, would protect earth from most other major impact events, but for the next several billion years the planet was bombarded as it had little atmosphere to protect itself and the outer planets were still clearing smaller debris. Life formed about a billion years ago, after billions of years of bombardment by comets and ice and organic rich meteorites. These comets and meteorites had brought water and complex molecules, forming oceans. The planet's volcanic activity had largely subsided, and life formed around volcanic undersea vents in the now-stable and organic-rich oceans. Earth went through several phases of life, each punctuated by a mass extinction, and the most recent mammalian epoch has seen the recent and rapid rise of humans.

Etymology
The modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was already being used to translate the many senses of Latin terra and Greek γῆ gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ('Earth'), a giantess often given as the mother of Thor.

Historically, earth has been written in lowercase. From early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, and the earth was also written the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets, though earth and forms with the remain common. House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name (for example, "Earth's atmosphere") but writes it in lowercase when preceded by the (for example, "the atmosphere of the earth"). It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?"

Occasionally, the name Terra /ˈtɛrə/ is used in scientific writing and especially in science fiction to distinguish humanity's inhabited planet from others, while in poetry Tellus /ˈtɛləs/ has been used to denote personification of the Earth. The Greek poetic name Gaea (Gæa) /ˈdʒiːə/ is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is /ˈɡaɪə/ rather than the more Classical /ˈɡeɪə/.

There are a number of adjectives for the planet Earth. From Earth itself comes earthly. From the Latin Terra comes Terran /ˈtɛrən/, Terrestrial /təˈrɛstriəl/, and (via French) Terrene /təˈriːn/, and from the Latin Tellus comes Tellurian /tɛˈlʊəriən/ and Telluric.