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Unformatted text preview: Ch. 9: Precambrian Earth and Life History The Proterozoic Eon Key Words:- Laurentia- Orogenies and rifting- Proterozoic rocks Tillites Ophiolites Banded Iron Formations Continental Redbeds- First multicelled organisms o Ediacaran Fauna _______________________________________________________ ______ << Two typical rock in Archeon: Granite, >> The Proterozoic Eon- Nearly 2 billion years (42.5 % of Earths history)- Subdivided into 3 eras (Paleo, Meso, and Neo) and 10 Periods- Began at 2.5 b.y. o Change in style of crustal evolution Archean: greenstone belts and granite-gneiss complexes; metamorphosed; cratons Proterozoic: many rocks with low or no deformation, widespread sedimentary rock assemblages, plate tectonics like today Often separated by <<huge>> uncomformity- First oxygen-dependent organisms 1 Proterozoic Continents: __Laurentia___ - N-America, Greenland, parts of NW Scotland, parts of Scandinavia (Baltic shield)- 2.0-1.8 b.y.: o Collision of various plates o Orogens formed (linear or arcuate deformation belts,...
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