page - 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 isotope-dating Earth has changed over time Atmosphere, weather, positions of continents The geological record The fossil record Continental drift Recent mammalian extinctions 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. 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)
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2 Radioisotope dating The earth is ancient and changing: Oxygen concentration Sea levels Temperature and humidity Meteors and comet impacts Continental Drift Oxygen concentration increasing
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3 Sea levels have changed repeatedly. * Indicates mass extinctions of marine organisms 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 2-km asteroid - 1 per 500,000 years
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4 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, shattering the tile floor of the second-floor bathroom and embedding itself in a wall. NY Times Jan. 3 2007 Fig. 25-7 Animals Colonization of land Paleozoic Meso- zoic Humans Ceno- Origin of solar system and Earth Prokaryotes Proterozoic Archaean Bilions of years ago 1 4 3 2 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen
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5 Precambrian Era (4.5 bya-543 mya) White Island, New Zealand Precambrian Era (4.5 bya-543 mya) Evolutionary milestone #1: Life arises “Primordial ooze” Evolutionary milestone #2: Cells form Prokaryotic cell Precambrian Era (4.5 bya-543 mya)
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6 Evolutionary milestone #3: Photosynthesis Cyanobacteria: blue-green bacteria Precambrian Era (4.5 bya-543 mya) Precambrian Era (4.5 bya-543 mya) Evolutionary milestone #4: Sex happens Bacterial conjugation Precambrian Era (4.5 bya-543 mya)
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