Soft parts do not fossilize well and most organisms

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- Soft parts do not fossilize well (and most organisms are entirely soft!) - Recycling of crust due to plate tectonics and erosion means that old rocks are rarer than young rocks - Rocks in some areas are not visible (forested land) - Some luck involved in finding fossils... Strengths of the fossil record - Fossils are the remains of organisms and their products that actually existed. Very important, even when limited. Window into the past - Excellent fossil records exists for some groups (e.g., clams) and some structures (e.g., teeth). - Overall, the fossil record is much better than most people think: millions of fossils have been found
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Geological Time Scale Precambrian Fig. 2.31 PBS: Eons A brief history of geologic time 201 201 The Origins of Life 202 W3.L1
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Outline - How old is the earth? - What is the 1st evidence for prokaryotic life? - Where did life come from? - Extraterrestrial theories - Oparin-Haldane theory - RNA world 203 How old is the earth? - Earth formed by the collision and coalescence of solar debris after the formation of the sun - Radiometric dating of meteorites: 4.543 byr (just remember 4.5 byr) - This is the the age of the solar system and the earth, or at least the material and became the earth Solar System condenses from interstellar dust cloud Earth forms 4.543 byr ago Universe begins with Big Bang 16 byr ago 204 Earth forms 4.543 byr ago Heavy bombardment ends 4 byr ago Oldest rocks 4.0 byr old - No rocks survive from when the earth formed - 500 myr needed to cool the surface - Oldest minerals 4.4 byr old (found in Australia) - Oldest rocks 4.0 byr - Heavy Bombardment: Comets & Asteroids peppered all the planets in our solar system (including Earth) from ~4.1 to 3.8 byr - Early atmosphere toxic, not at all like today (no O 2 ) How old are the rocks? 205
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4.53 by ago a Mars-sized body called Theia collided with the molten earth -- Theia merged with the earth, creating its present size -- The material that splashed off of earth at impact coalesced into the moon -- The collision tilted the earth’s orbital plane 23 degrees. If the earth wasn’t tilted, there would be no yearly seasons! -- If a collision like this happened today, all the oceans on earth would instantly evaporate (not good) 206 Outline - How old is the earth? - What is the 1st evidence for prokaryotic life? - Where did life come from? - Extraterrestrial theories - Oparin-Haldane theory - RNA world 207 The early forms of life went extinct long, long ago Last Universal Common Ancestor (LUCA) 208 - No clear physical remains of the origins of life - Indirect evidence only
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True Cells 3.26 byr old fossils of dividing prokaryotic cells (from South Africa) fossils real cells 209 Stromatolites Modern stromatolites formed by bacteria Shark Bay, Australia Fossil stromatolite 3.5 BY old Abundant fossils Layers are produced as sediment precipitates over a growing mat of cyanobacteria 210 Evidence of photosynthesis from C isotope ratios
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