HistoryofLife - Geologic Timescale Chapters 19 20 History...

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2/27/11 1 History of Life on Earth Geologic Timescale Earth’s history is divided into four eras : Precambrian Paleozoic Mesozoic (dinosaurs) Cenozoic (most recent) Division of Time Eras subdivide into Periods Divided when drastic changes occur in the fossil record Often, mass extinction (big reduction in number of species) Permian extinction: lost 96% Geographic Forces Climate change cooling (Ice Age) or warming Asteroid Bombardment severe impacts cloud atmosphere, cut off sunlight Continental Drift Continental Drift Surface of Earth (crust) is plates They move around on molten core
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2/27/11 2 Consequences of Continental Drift Global cooling or warming influenced by how much land mass is at poles Isolated continents have unique species (geographic isolation) Example: Australia broke off before placental mammals evolved How Did Life Begin? Molecules must have been first Chemical reactions that grew in complexity? Self-replicating molecules like nucleic acids? We can’t be sure, but some events have been shown to be reasonably possible Stanley Miller’s experiments Earth’s early atmosphere: methane, ammonia, etc. Electrical energy easily shown to produce simple organic molecules, such as amino acids Natural Selection As soon as you have a replicating
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HistoryofLife - Geologic Timescale Chapters 19 20 History...

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