Lecture+15+Earth+History

Lecture+15+Earth+History - Lecture 15 Earth History Figure...

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Unformatted text preview: Lecture 15 Earth History Figure 12.7 Origin of the atmosphere Origin of the atmosphere and oceans and oceans • Water vapor condensed to form clouds and rainwater that formed the oceans • About 3.5 billion years ago, photosynthesizing bacteria began to release oxygen • Oxygen levels steadily increased over time • Eventually oxygen levels were sufficient for ozone to develop in the atmosphere Origin of the atmosphere Origin of the atmosphere and oceans and oceans • Outgassing produced acidic conditions that caused an accelerated rate of weathering of Earth’s rocky surface • Products of this weathering were carried to the oceans, thus increasing the salinity of the oceans • Oceans also served as a depository for carbon dioxide Figure 12.6 Stromatolites Photosynthesis CO 2 + H 2 O ↔ CH 2 O + O 2 Carbon Dioxide Controls Calcite Dissolution and Precipitation CaCO 3 + CO 2 + H 2 O ↔ Ca2+ + 2HCO 3- Figure 12.8 Precambrian history Precambrian history • The Precambrian, which is divided into the Archean and the Proterozoic eons, spans almost 90% of Earth’s history • Much of Earth’s stable continental crust was created during this time – Partial melting of the mantle formed volcanic island arcs and ocean plateaus – These crustal fragments collided and accreted to form larger crustal provinces Precambrian history Precambrian history • The Precambrian, which is divided into the Archean and the Proterozoic eons, spans almost 90% of Earth’s history • Much of Earth’s stable continental crust was created during this time – Larger crustal areas were assembled into larger blocks called cratons – Cratons form the core of modern continents Formation of Formation of continental crust continental crust Figure 12.12 Figure 12.13 Figure 12.14 Precambrian history Precambrian history • Supercontinents • Large landmasses that consist of all, or nearly all, existing continents • Pangaea was the most recent, but perhaps an even larger one, Rodinia...
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This note was uploaded on 10/22/2008 for the course EAS 2600 taught by Professor Ingalls during the Fall '08 term at Georgia Tech.

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Lecture+15+Earth+History - Lecture 15 Earth History Figure...

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