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Unformatted text preview: Geol test 3 March 12, 2007 ????? first section of notes • Now use the methods of “calibrate” geological time scale based on sedimentary rocks only, and RADIOMETRIV AGES ONLY POSSIBLE FOR IGNEOUS ROCKS. • SEDIMENTARY ROCKS CANNOT BE RADIOMETRICALLY DATES • For sedimentary rock, :age: is when sediment laid down (fossil enclosed) detritial sedimentary rocks contain broken solid grains • Best method- date ash beds found mixed with sedimentary rocks. These follow the principal of superposition. o Rocks above ashbed are younger. o Rocks below ash bed are older • Important examples of dating o U-PB METHOD Age of the earth- 4500m.y.- based on dating of meteriorites formed at the same time as the earth Explotion of life forms at base of palezioc occurred ~55o m.y. ago Faunal extinction event at palezioc-mezezioc boundry occurred ~22o m.y. ago o K-AR METHOD Funaul extinction event at mezezoic- cenozioc boundry occurred 65 m.y. ago Man like creatures first appeared in east Africa ~5 n.y. ago...
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This note was uploaded on 04/28/2008 for the course GEOG 1003 taught by Professor Patzewitsch during the Spring '08 term at LSU.
- Spring '08