Lecture 2

Lecture 2 - A brief history of life on earth The earth is...

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1 A brief history of life on earth The earth is ancient and how we know Earth has changed over time The geological record The fossil record Continental drift Recent mammalian extinctions Earth 4.5 billion years old History of life - imagine earth’s age as 1 year 1st life late March 1st marine animals late October Dinosaurs extinct Dec 26 mammals start to diversify Human-chimpanzee lineages diverge 13 hrs before midnight Christ born 13 seconds before midnight The fossil record Nicholaus Steno (1638-1686) Law 1: In a sequence of sedimentary rocks, the layers of rocks were originally formed by lying horizontally. Law 2: In a sequence of sedimentary rocks, the oldest are lowest and the youngest are the highest. 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 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 (Permian)
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2 Radioactive-isotopes Half-life 32 P = 14.3 days ( 31 P) 3 H = 12.3 years 14 C = 5700 years ( 12 C) 40 K = 1.3 billion years ( 40 Ar) Radioisotope dating Every isotope has characteristic half-life Different isotopes used to date different things The earth is ancient and changing: • Oxygen concentration • Sea levels • Temperature and humidity • Meteors and comet impacts • Continental Drift Oxygen concentration increasing Sea levels have changed repeatedly. * Indicates mass extinctions of marine organisms
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3 Hot-humid and cold- dry conditions have fluctuated. Indicates when large areas of the earth’s surface was covered by glaciers Meteorite and Comet Impacts Pea-size meteoroids - 10 per hour Walnut-size - 1 per hour Grapefruit-size - 1 every 10 hours Basketball-size - 1 per month 1-km asteroid - 1 per 100,000 years FREEHOLD TOWNSHIP, N.J., Whatever it was, the object that fell from the sky was not part of an airplane. That was all anyone knew for sure.It was dense with a rough metallic surface. The oblong object was only about two inches long - fitting into the palm of a hand - but weighed almost a pound. And it fell through the roof of a two-story house here Tuesday afternoon,
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Lecture 2 - A brief history of life on earth The earth is...

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