GEO 101 Lecture 12: Geology Chapter 11

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Geology chapter 11: algal bloom (phytoplankton)- crimson tide , white cliffs of dover england. Spans earth"s formation (4,540 mya) to first preserved crustal rocks (4,000 mya) Differentiation occurred causing heaving metals (core) to separate from lighter elements (crust) Earliest rocks were likely destroyed by period of intense meteorite impacts (3,900 mya) Early atmosphere: water, carbon dioxide, methane, ammonia, hydrogen, nitrogen, sulfur dioxide: the archean eon. Begins with first appearance of continental crust. Oceans were present have been ever since. First life thought to be present (3,800- 3,500 mya) based on: chemical (molecular) fossils, or biomarkers isotopes signatures fossil forms (fossilized bacteria) Stromalites- distinctive mounds of sediment produced by mats of cyanobacteria (microscopic) Oldest undisputed evidence of life (3,200 mya) Atmosphere: high in carbon dioxide and nitrogen, little oxygen: the proterozoic eon. Spans almost half of earth"s history (longest eon) Larger plates and continents formed (90% of continental crust) Shields formed (broad, low-lying region of exposed precambrian rock)

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