EAS201 Lecture Notes - Lecture 28: Anoxygenic Photosynthesis, Isotope Fractionation, Pyrite
22 Mar 2020
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Goe is pretty well defined at starting at 2. 5 and lasted until 2. 3. Green = reducing atmosphere and ocean (no oxygen) Before 2. 4 bya theres mif = no oxygen. Rusty sandstone (iron has been oxidized and crystallized in the sandstone) Between 2. 3-2. 4 bya theres oxygen around to cause oxidation. In the absence of o2, these minerals will be preserved. If these are preserved, there wasn"t enough o2 to oxidize these minerals. When you find mn 2-4 you know oxygen is present. Cr, u if these are present you know there is o2 present. Chemically precipitated sediment that are iron and silica rich. Can track what happened to seawater chemistry at that time. Formed by bacteria oxidizing dissolved fe (ii) in seawater to form ferric hydroxide minerals. Debate about whether this process required oxygenic photosynthesis or anoxygenic photosynthesis. Likely that bif initially formed through anoxygenic photosynthesis from ancient purple bacteria, and then when cyanobacteria evolved they formed by oxygenic photosynthesis.
