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Unformatted text preview: 1 Geological History I- Origin of the Sun & the Solar system I) Big Bang: 20 billion yrs ago II) The nebular hypothesis: • T drops following the Big Bang • 5 billion yrs ago: our own solar nebula collapses into a disk shaped • Solar winds. • Accretion: Planetesimals and protoplanets III) Earth evolution: • Accretion causes an increase in the T • Differentiation of the Earth into crust, mantle, and core. • Earth acquires its magnetic field during the Early Precambrian. IV) Earth’s early atmosphere • Outgassing • Rich in H 2 O, CO 2 and N 2 • Precipitation and the beginning of the hydrologic cycle. • How did it evolve to the present composition? ⇒ Cyanobacteria & plants. II- The Precambrian “Era” The Precambrian spans about 88% of Earth's history Between 4.5 billion years ago and ending approximately 540 million years ago Represented in the cores of the continents known as “shields” Important rock types: Greenstones and “granitoids”, Granulite facies metamorphic rocks....
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- Fall '08
- Geology, Gondwana, Geological history of Earth, Early Paleozoic