The modern English noun earth developed from Middle English erthe (recorded in 1137), itself from Old English eorthe (dating from before 725), deriving from Proto-Germanic *ertho. Earth has cognates in all other Germanic languages, including Dutch aarde, German Erde, and Swedish, Norwegian, and Danish jord.[31] The Earth is personified as a goddess in Germanic paganism (appearing as Jörð in Norse mythology, mother of the god Thor).[32]
In general English usage, the name earth can be capitalized or spelled in lowercase interchangeably, either when used absolutely or prefixed with "the" (i.e. "Earth", "the Earth", "earth", or "the earth"). Many deliberately spell the name of the planet with a capital, both as "Earth" or "the Earth". This is to distinguish it as a proper noun, distinct from the senses of the term as a mass noun or verb (e.g. referring to soil, the ground, earthing in the electrical sense, etc.). Oxford spelling recognizes the lowercase form as the most common, with the capitalized form as a variant of it. Another common convention is to spell the name with a capital when occurring absolutely (e.g. Earth's atmosphere) and lowercase when preceded by "the" (e.g. the atmosphere of the earth). The term almost exclusively exists in lowercase when appearing in common phrases, even without "the" preceding it (e.g. "It does not cost the earth.", "What on earth are you doing?").[33]
Chronology
Formation
Main article: History of the Earth
Artist's impression of the birth of the Solar System
The earliest material found in the Solar System is dated to 4.5672±0.0006 bya;[34] therefore, it is inferred that the Earth must have been formed by accretion around this time. By 4.54±0.04 bya[23] the primordial Earth had formed. The formation and evolution of the Solar System bodies occurred in tandem with 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 in tandem with the star. A nebula contains gas, ice grains and dust (including primordial nuclides). In nebular theory planetesimals commence forming as particulate accrues by cohesive clumping and then by gravity. The assembly of the primordial Earth proceeded for 10–20 myr.[35] The Moon formed shortly thereafter, about 4.53 bya.[36]
The Moon's formation remains debated. The working hypothesis is that it formed by accretion from material loosed from the Earth after a Mars-sized object dubbed Theia impacted with Earth.[37] The model, however, is not self-consistent. In this scenario, the mass of Theia is 10% of the Earth's mass,[38] it impacts with the Earth in a glancing blow,[39] and some of its mass merges with the Earth. Between approximately 3.8 and 4.1 bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon, and by inference, to the Earth.
Kamis, 18 Oktober 2012
In general English usage, the name earth can be capitalized or spelled in lowercase interchangeably,
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