Lecture_11 - Past Climate Change 1.0 Time Span of Climate...

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Past Climate Change 1.0 Time Span of Climate Records Present average surface temperature of Earth ~15 ° C Past temperatures and climate obtained from multiple geologic and historical sources. 2.0 Proterozoic and Paleozoic Glaciations Ancient erosion surfaces and glacial deposits in rock record indicate global cooling occurred several times throughout Earth’s history. Paleoproterozoic glaciation ~ 2.2-2.4 billion years ago : First evidence for glaciation (Huronian) found in North America, Finland, South Africa, Australia, and India. Paleogeographic reconstruction indicates formation of high-latitude ice sheets. High CO 2 in atmosphere offset by “faint Sun”. As more land covered by ice chemical erosion of surface suppressed which led to buildup of CO 2 in atmosphere and subsequent warming of Earth. During glaciation cold oxygenated polar waters probably flowed for first time through deep ocean, mixing formerly stratified water column. Faint-Sun Paradox: Most main-sequence stars like our Sun gradually increases in luminosity with time, which means that solar constant was some tens of percent less a few billion years ago than it is today. A paradox arises: how could the solar constant have been that low and Earth escaped freezing solid? Answer: the added "greenhouse effect" of more CO 2 in atmosphere at that time. Neoproterozoic glaciation ~ 850 to 600 million years ago. Evidence for most extensive series of glaciations found in all continents but Antarctica. Paleogeographic reconstruction indicates formation of low-latitude ice sheets. Suggests
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widespread and prolonged episodes of cooling. Cycle eventually broken by continental fragmentation. Carbonates interlayered with tillites indicates rapidly
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This note was uploaded on 07/25/2008 for the course ISP 203A taught by Professor Larson during the Fall '08 term at Michigan State University.

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Lecture_11 - Past Climate Change 1.0 Time Span of Climate...

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