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Unformatted text preview: 1 Overview • Earth: long complex history • Formation of the Solar System • Splitting and colliding of continents. • Many of the changes on the planet Earth occur at a “snail’s pace,” generally too slow for people to perceive • Learn earth history from the rock record How Old? Many methods ... • Begats method: direct Biblical interpretation • James Ussher 1650~6,000yrs • Young age has been taken for granted in western world • Hindu calendar the year 2000 A.D. would be 1,972,949,101 yrs • Cooling of Earth: mathematical calculation based on the rate of cooling of an initially molten earth • Lord Kelvin 1865, 40-20 my How Old? Many methods ... • Salinity – salt in ocean, linked to erosion • John Joly, 1899: 90 my • Sedimentary rocks record: total thickness of sedimentary rocks divided by annual deposition • “various geologists” 100 my • Radioactivity [Becquerel 1896]: based on the ratio of radioactive uranium to stable lead in rocks • Boltwood 1905 500 my, • 1907 1.6 by, • oldest zircons found are 4.3 by, extrapolation arrives at 4.6 by How Old? Many methods ... • James Hutton, the“father of geology”: • observable geologic processes would require vast amounts of time to produce the mountains, valleys, etc., we see on Earth today • Charles Lyell; • popularized Hutton’s work and concepts in his book, Principles of Geology • Uniformitarianism / actualism: • same processes and natural laws that operated in the past are operating at present - “The present is the key to the past”...
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This note was uploaded on 04/07/2008 for the course GEOL 111 taught by Professor Pinter during the Spring '08 term at SIU Carbondale.
- Spring '08