Diferenzas entre revisións de «Arcaico»

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An explanation for the general lack of Hadean rocks (older than 3800 Ma) is the amount of extrasolar debris present within the early solar system. Even after planetary formation, considerable volumes of large [[asteroid]]s and [[meteorite]]s still existed, and bombarded the early Earth until approximately 3800 Ma. A barrage of particularly large impactors known as the [[late heavy bombardment]] may have prevented any large crustal fragments from forming by literally shattering the early protocontinents.
 
===ArcheanA palaeoenvironmentAtmosfera Arcaica===
The Archean atmosphere is thought to have lacked free [[oxygen]]. Temperatures appear to have been near modern levels even within 500 Ma of Earth's formation, with liquid water present, as evidenced by certain highly deformed [[gneiss]]es produced by metamorphism of [[sediment]]ary [[protolith]]s. Astronomers think that the sun was about one-third dimmer than at present, which may have contributed to lower global temperatures than otherwise expected. This is thought to reflect larger amounts of greenhouse gases than later in the [[History of Earth|Earth's history]].
 
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