Diferenzas entre revisións de «Arcaico»

 
==A Terra Arcaica==
No principio do Arcaico, a calor interna da [[Terra]] era preto de 3 veces maior que na actualidade, e aínda dúas veces maior que o seu nível a principio do [[Proterozoico]] (2,500 {{MA}}). A calor calor era a remanente do proceso de acrección planetaria, parciamente procedente da calor de formación do núcleo interno formado por ferro, e parcialemente procedente da calor radioactva pola corta vida de átomos radioactivos como o [[uranio]]-235.
 
A maioría das rochas arcaicas que podemos observar na actualidade son [[rochas metamorficasmetamórficas|metamorficametamórfica]s] e [[ígneas rocha ígnea]]s. A actividade [[Volcán|Volcánica]] era considerablemente maior que a actual, con numerosos [[Hotspot (xeoloxía)|hot spot]]s, [[rift valley]]s, e erupción de lavas incluindo tipos inusuais como [[komatitas]]. Sen embargo as rochas ígneas intrusivas predominan dentro dos [[cratón]]s procedentes da codia do Arcaico sobreviven hoxe. These are magmas which infiltrated into host rocks, but solidified before they could erupt at the Earth's surface. Examples include great melt sheets and voluminous plutonic masses of [[granite]], [[diorite]], [[layered intrusion]]s, [[anorthosite]]s and [[monzonite]]s known as [[sanukitoid]]s.
 
The Earth of the early Archean may have had a different tectonic style. Some scientists think that because the Earth was hotter, [[plate tectonic]] activity was more vigorous than it is today, resulting in a much greater rate of recycling of crustal material. This may have prevented [[craton]]isation and continent formation until the mantle cooled and convection slowed down. Others argue that the subcontinental lithospheric mantle was too buoyant to [[subduct]], and that the lack of Archean rocks is a function of erosion by subsequent tectonic events. The question of whether or not plate tectonic activity existed in the Archean is an active area of modern geoscientific research. <ref>Stanley, Steven M. ''Earth System History.'' New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 p. 297-301</ref>
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