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timeandgeology - Overview Earth long complex history...

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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” Relative vs. Numerical Age
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