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Geog. 110 Notes 3

Geog. 110 Notes 3 - -evolution of the atmosphere-largely...

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- evolution of the atmosphere: -largely occurred during Precambrian Eon; when did the following become established? algae/ bacteria (late Precambrian Eon), shelled creatures (beginning of Paleozoic Era), forests (end of Paleozoic Era), dinosaurs (Mesozoic Era), mammals, humans (right at top of Cenozoic Era) -brief history of Earth’s evolution -4.5 billion years ago: chemical composition (methane, ammonia, CO, and CO2), geothermal equilibrium (highly stable), temperature (relatively mild and similar to today w/ a few extremes), Sun’s output (30-40% less than today), meteor/ asteroid impacts (much more common than today) -1-2 billion years ago: rapid evolution of life (anaerobic to aerobic organisms, leading to photosynthesis), change in atmospheric chemistry (atmosphere dominated by nitrogen 78%, oxygen 21%, both of which are byproducts of life); what happened to Precambrian CO2? largely stored in rocks such as limestone, inside the Earth -why do oxygen levels stay relatively constant in the atmosphere?: negative feedback -how has life altered Earth’s atmosphere?: significantly lowered amount of CO2 in
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