ENV100Y5 Lecture 4: env100 part 4
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ENV100Y5 Full Course Notes
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Document Summary
The atmosphere and hydrosphere have changed over time: earths early atmosphere, primitive vs. Fossil: remnant of long dead organism, preserved in stone. Fossil record: information about the history of past life. Species have come and gone, and new life forms have evolved thought earth history. Trace fossils- traces of the animals, not actual fossils. Not all fossils are macrofossils: chemical evidence in the rock by some processes that was caused by life - shows life was here. Early life forms: chemosynthetic, thermophilic (heat-loving) bacteria, photosynthetic cyanobacteria (blue-green algae) Life had two main influences on chemistry of the atmosphere: build up of o2, removal of co2. Cyanobacteria, use up of co2 and emit o2: photosynthetic organism, aerobic (oxygen-tolerant, ability to form colonies - stromatolites, rate of oxygen build up increased. Seafloor sediments recorded changing ocean atmosphere compositions: red-black banded iron formation (bif, shows that the atmosphere was fluctuating between reduced and oxygenated, black - reduced iron, red - oxidized.
