Autor Thema: 'Recycling' der Erdkruste begann vor drei Milliarden Jahren  (Gelesen 610 mal)

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'Recycling' der Erdkruste begann vor drei Milliarden Jahren
« am: März 16, 2012, 17:37:35 nachm. »
'Recycling' der Erdkruste begann vor ca. drei Milliarden Jahren

http://www.physorg.com/news/2012-03-isotopes-recycling-earths-crust-began.html

auch als Hörtext: news251109416.mp3

Zitat
Specifically, they found that during the first billion and a half years of Earth’s existence, the rate of new crust formation was quite high (presumably due to meteorite collisions), at about 3 cubic kilometers annually which resulted in the creation of roughly sixty five percent of its current composition. About three billion years ago, however, smaller amounts of new material were created and more of the crust was simply recycled with material from the mantle.

As a result of this change, the tectonic plates we see today began forming, growing ever more solid as the years passed, leading to the shifting that causes changes to the shape and location of the continents.

A Change in the Geodynamics of Continental Growth 3 Billion Years Ago, Science 16 March 2012: Vol. 335 no. 6074 pp. 1334-1336.

http://www.sciencemag.org/content/335/6074/1334

Zitat
Models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout Earth’s history. The oxygen isotopic composition of zircons, for which uranium-lead and hafnium isotopic data provide age constraints, is a key archive of crustal reworking. We identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time. Growth of continental crust appears to have been a continuous process, albeit at variable rates. A marked decrease in the rate of crustal growth at ~3 billion years ago may be linked to the onset of subduction-driven plate tectonics.

Martin

 

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