112-pp17 - UNIVERSITY OF SOUTH ALABAMA Last time we...

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1 GY 112: Earth History The Atmosphere and Hydrosphere UNIVERSITY OF SOUTH ALABAMA Last time we covered… 1) The Hadean (4.6 to 4.1 GA) 2) The Archean (4.1 to 2.5 GA) Time Frame Tectonics and Paleogeography Life forms • The first usage of the term Archean is credited to Sir William Logan, a geologist with the GSC (Geological Survey of Canada) • He was studying very old rocks in northern/central Canada • “PreCambrian” granites and metamorphic rocks (no fossils), called the Canadian Shield The Archean Eon •Sh ie ld : very old (>2.5 GA) igneous and metamorphic “basement” rocks (Granulites) •P la t fo rm : younger (550 MA-2.5 GA) sedimentary rocks The Canadian Shield ht p:/ mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif Archean Tectonics Early continental crust = Tonalite (today it’s granite) Early oceanic crust = Komatiite (today it’s basalt) And the continents have been growing by accretion ever since • One of the most interesting tectonic components in shield areas of the word are greenstone belts
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2 Today’s Agenda The Atmosphere and Hydrosphere (web notes 17)
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This note was uploaded on 02/04/2012 for the course GLY 112 taught by Professor Haywick during the Spring '12 term at S. Alabama.

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112-pp17 - UNIVERSITY OF SOUTH ALABAMA Last time we...

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