Lecture 12

Lecture 12 - Lecture 12- Life before Animals A. Evidence of...

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Lecture 12- Life before Animals A. Evidence of Earliest Life on Earth- e Three lines of evidence point to life arising quite early in Earth’s history o Chemical evidence (~3.85 Ga) o Stromatolites (~3.5 Ga) o Microfossils (~3.2-3.5 Ga) e 3.85 Ga Origins- Evidence comes from the analysis of carbon isotopes in ancient metamorphic rock, there is geological evidence B. Stromatolites- Laminated accretionary structures made of carbonate rock e Laminated there is a very fine layering and the growth is accretionary which means it successively builds or grows e Growths by layers that build up by microbial action, the CaCo3 is precipitated over the growing mats e Sediments are trapped by sticky mucilage and the microbes build up through sediments and start a new layer C. Modern Stromatolites- Living stromatolites contain layers of sediment intermixed with different types of microbes e They are very rare today and most exist in extreme environments and that are protected from predators D. Microfossils- e Cyanobacteria uses sunlight as a primary energy source e Cells can get energy in one of the three ways o From sunlight, from organic compounds, or from inorganic compounds o They use sunlight for energy and generate oxygen as a waste product e 3.5 Ga NW Australian microbe- chemical analysis showed it did contain some organic
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Lecture 12 - Lecture 12- Life before Animals A. Evidence of...

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