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Lecture 14B - Overview History of Life on Earth I Fossils...

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1 Overview – History of Life on Earth I. Fossils II. Geologic time scale III. Extinctions IV. Dating V. Earth has changed over time VI. Fossil record VII. Continental Drift II. Geological Time Scale : Developed before Darwin Based on distinctive fossil taxa Originally based relative ages (younger rocks lie on top of older ones) Some boundaries - mass extinctions Tertiary III. Extinction Background extinction - extinctions that occur at normal rate (most extinctions) Mass extinction - large percentage of species go extinct within short period of time (global event, broad range of organisms, rapid relative to expected lifespan of taxa) (families) end of Mesozoic (K/T) end of Paleozoic Era (Permian) IV. Dating fossils A. Relative ages B. Absolute ages Radioisotope dating isotopes - varieties of an element with different mass (different # neutrons) 14 C, 12 C Radioactive isotopes - unstable – decay spontaneously into different element/isotope particular , constant rate not effected by temperature, moisture, etc. Radioisotope dating Half-life - amount of time for half of parent isotope to decay into daughter isotope
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2 Every isotope has characteristic half-life Different isotopes used to date different things V. The earth has changed over time Hot-humid and cold-dry conditions have fluctuated.
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