Geological Time


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  • Geological Time

    1. 1. Geological Time
    2. 2. Age of the Earth (1): Eternity <ul><li>Aristotle (384-322 BC) </li></ul><ul><li>In classical philosophy the Earth was </li></ul><ul><li>eternal , so Age of the Earth irrelevant </li></ul>© NASA
    3. 3. Age of the Earth (2): The Bible 4004 BC <ul><li>In 1654 Bishop Ussher calculated that the Earth was created in 4004 BC </li></ul><ul><li>He got this figure using evidence from the Bible and other Middle Eastern literature </li></ul><ul><li>The date became so popular that it was printed with the Book of Genesis </li></ul>Bishop Ussher (1581-1656)
    4. 4. Age of the Earth (3): Experiments Comte de Buffon (1707-1788) <ul><li>In 1760, Buffon </li></ul><ul><li>measured the cooling </li></ul><ul><li>time of red-hot iron </li></ul><ul><li>balls of different sizes </li></ul><ul><li>He scaled up to the </li></ul><ul><li>size of the Earth </li></ul><ul><li>(75,000 years to cool) </li></ul> Buffon_1707-1788.jpg One of Buffon’s iron balls
    5. 5. Age of the Earth (4): The Sun Hermann_von_Helmholtz.jpg Hermann von Helmholtz (1821-1894) <ul><li>In 1858, calculated the time it would </li></ul><ul><li>take for the sun to condense to </li></ul><ul><li>present diameter from gas nebula </li></ul><ul><li>(around 20 million years) </li></ul>
    6. 6. Age of the Earth (5): More Physics Kelvin_photograph.jpg Lord Kelvin (1824-1907) <ul><li>In 1862, Lord Kelvin </li></ul><ul><li>assumed that Earth </li></ul><ul><li>originally had a </li></ul><ul><li>temperature of 7000°F </li></ul><ul><li>Knew geothermal </li></ul><ul><li>gradient (1°F/50 ft) </li></ul><ul><li>Calculated cooling age </li></ul><ul><li>(20 million years) </li></ul>Geothermal gradient
    7. 7. Age of the Earth (6): Geology Charles Lyell (1797-1875) <ul><li>Sediment accumulates at the same rate </li></ul><ul><li>today as in the past so Earth must be really </li></ul><ul><li>ancient to account for geological record </li></ul><ul><li>(hundreds of millions of years) </li></ul>
    8. 8. Age of the Earth (7): Evolution Lord Kelvin’s “views on the recent age of the world have been for some time one of my sorest troubles” (Darwin to Wallace) <ul><li>In 1869, Thomson </li></ul><ul><li>argued that there was </li></ul><ul><li>not enough time </li></ul><ul><li>for Darwin’s evolution </li></ul><ul><li>by natural selection </li></ul> Lord_Kelvin_photograph.jpg Charles Darwin Lord Kelvin Darwin aged 54.jpg
    9. 9. Age of the Earth (8): Sea Salt <ul><li>In 1899, John Joly calculated the Earth’s </li></ul><ul><li>age using the saltiness of the ocean </li></ul><ul><li>(80-150 million years) </li></ul><ul><li>How much salt was in the Ocean? </li></ul><ul><li>How much did rivers add each year? </li></ul>Obituary Notices of F.R.S. , 1 , 260 (1933) John Joly (1857-1933) salt crystals
    10. 10. Age of the Earth (9): Assumptions <ul><li>All these estimates </li></ul><ul><li>were based on </li></ul><ul><li>assumptions that </li></ul><ul><li>couldn’t be proven </li></ul>
    11. 11. Geological History (1): Strata Nicolas Steno (1638-1686) Oldest strata Youngest strata © Howard Falcon-Lang
    12. 12. Geological History (2): Neptunism Abraham Werner (1749-1817) Gottlob_Werner.jpg <ul><li>Werner argued all rocks </li></ul><ul><li>had been deposited in </li></ul><ul><li>a worldwide ocean </li></ul><ul><li>(think Noah’s Flood) </li></ul><ul><li>Geologists could figure </li></ul><ul><li>out the order in which </li></ul><ul><li>rocks formed </li></ul><ul><li>Divided geological record </li></ul><ul><li>into four main divisions </li></ul>© Howard Falcon-Lang Granite
    13. 13. Geological History (3): Gaps <ul><li>Hutton’s unconformity showed that there </li></ul><ul><li>were big gaps in the geological record </li></ul>James Hutton (1726-1797) Copyright © Marli Miller, University of Oregon commons/c/c6/James_Hutton.jpg Siccar Point unconformity
    14. 14. Geological History (4): Maps William Smith (1769-1839) William_Smith.g.jpg The Map that changed the World Some of Smith’s fossils
    15. 15. Geological History (5): Fossils Cuvier <ul><li>Cuvier showed that </li></ul><ul><li>some animals had </li></ul><ul><li>gone extinct </li></ul><ul><li>Lyell used the </li></ul><ul><li>proportion of living </li></ul><ul><li>fossils to divide up </li></ul><ul><li>geological time </li></ul><ul><li>Older rocks contained </li></ul><ul><li>more extinct types </li></ul><ul><li>than younger rocks </li></ul>Charles Lyell (1797-1875) Georges Cuvier (1769-1832)
    16. 16. Geological History (6): Stratigraphy A tug-of-war as rocks got sorted into geological periods in the new science of stratigraphy :Adam_Sedgwick.jpg _Murchison.jpg Murchison Sedgewick
    17. 17. Geological History (7): Periods Carboniferous Cambrian Ordovician Silurian Devonian Permian Triassic Jurassic Cretaceous Tertiary Quaternary
    18. 18. Geological History (8): The Column Geological Time: Eons, Eras, Periods and Epochs
    19. 19. Geological History (9): Example Impact _event.jpg e_Tyrannosaurus_rex_p1050042.jpg Extinction Cretaceous Paleogene
    20. 20. Radiometric dating (1): Discovery Henri Becquerel (1852-1908) <ul><li>In 1896, Discovery of radioactivity paved </li></ul><ul><li>the way for the precise dating of events </li></ul><ul><li>in the geological record </li></ul>
    21. 21. Radiometric dating (2): Decay <ul><li>Radioactive ‘parent isotopes’ spontaneously emit protons and </li></ul><ul><li>neutrons and decay into ‘daughter isotopes’ </li></ul><ul><li>E.g., Uranium-238 decays into Lead-206 </li></ul>
    22. 22. Radiometric dating (3): Half life <ul><li>The rate of decay from parent to daughter isotope depends on </li></ul><ul><li>its half life. The half life is the amount of time needed </li></ul><ul><li>for half the parent isotope to decay to daughter isotope </li></ul>Half life: 0 Half life: 1 Half life: 2 Linear Exponential
    23. 23. Radiometric dating (4): Clocks <ul><li>Different radioactive isotopes have different half lives </li></ul><ul><li>Isotopes with long half lives are useful for dating old rocks. It is important to use the right tool for the right job </li></ul>Decay series Half life 40 K to 40 Ar 1250 Ma 147 Sm to 143 Nd 1060 Ma 235 U to 207 Pb 704 Ma 238 U to 206 Pb 4468 Ma 14 C to 14 N 5370 years Geological timescales Archaeology
    24. 24. Radiometric dating (5): Pioneers Arthur Holmes (1890-1965) Ernest Rutherford (1871-1937) <ul><li>Rutherford figured out a </li></ul><ul><li>technique to date the age </li></ul><ul><li>of rocks in 1904 </li></ul><ul><li>Holmes developed this </li></ul><ul><li>kind of ‘radiometric dating’ </li></ul><ul><li>still further. </li></ul><ul><li>In 1913 Holmes dated </li></ul><ul><li>some rocks from Ceylon </li></ul><ul><li>to 1600 million years </li></ul>
    25. 25. Radiometric dating (6): Oldest Rock <ul><li>Oldest rocks on Earth </li></ul><ul><li>are the Acasta Gniess of </li></ul><ul><li>northern Canada </li></ul><ul><li>4030 million years old </li></ul>© NASA Acasta Gneiss Zircon mineral
    26. 26. Radiometric dating (7): Oldest Grain 4404 Ma zircon grain © NASA <ul><li>Ancient mineral </li></ul><ul><li>grain found at </li></ul><ul><li>Jack Hills, Australia </li></ul><ul><li>Mineral grain eroded </li></ul><ul><li>from first crust and </li></ul><ul><li>then deposited in a </li></ul><ul><li>new rock </li></ul><ul><li>Dates the Earth’s </li></ul><ul><li>first crust to around </li></ul><ul><li>4404 million years </li></ul>
    27. 27. Radiometric dating (8): Meteorites <ul><li>Radiometric age of meteorites </li></ul><ul><li>date the formation of the </li></ul><ul><li>Solar System and Earth </li></ul><ul><li>(4550 million years old) </li></ul>Crab Nebula Canyon Diablo meteorite
    28. 28. Radiometric Dating (9): History dinosaurs humans first life origin of Earth © World Health Org. © NASA first complex cells
    29. 29. Geological Time © NASA
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