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 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) 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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2 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 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- zoic Origin of solar system and Earth Prokaryotes Proterozoic Archaean Billions of years ago 1 4 3 2 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen
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3 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) 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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