Hadean
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Template:Hadean Infobox The name Hadean refers to the geologic period before 3800 million years ago (mya). The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks. In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada and Western Australia. Some sources of information give other dates for the end of the Hadean period.
W. B. Harland later coined an almost synonymous term: the "Priscoan period".
The oldest known rock formations comprise somewhat altered sediments from Greenland dated around 3800 mya by a volcanic dike that penetrated the rocks after they were deposited. Individual zircon crystals redeposited in sediments in Western Canada and the Jack Hills region of Western Australia are much older. The oldest dated zircons date from about 4400 mya - very close to the hypothesized time of the Earth's formation. The Greenland sediments include banded iron beds. They contain possibly organic carbon and quite possibly indicate that photosynthetic life had already emerged at that time. The oldest known fossils (from Australia) date from a few hundred million years later.
The late heavy bombardment happened during Hadean times and affected the Earth more than it affected the Moon.
The etymology of the name "Hadean" is from Hades, Greek for "unseen" or "Hell" and suggesting the underworld or referring to the conditions on Earth at the time.
Template:Eon Footer Template:Hadean Footerde:Hadaikum et:Hadaikum es:Hadeico fr:Hadéen it:Adeano he:האדן nl:Hadeïcum ja:冥王代 pl:Hadeik pt:Hadeano sh:Had (period) fi:Hadeinen eoni zh:冥古宙