Week 6
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What is the earliest evidence of photosynthesis?
Bubble being produced in stromatolites The vertical growth of stromatolites is evidence of cyanobacteria reaching for the photic zone
What are three sources of evidence for oxygen proxies?
Mass independent fractionation of sulphur isotopes Iron redox geochemistry Uraninite
What is MIF of sulphur isotopes?
This is the separation of a mix of isotopes into their unique isotopes. The ratio of isotopes works as a geochemical proxy
What does MIF tell us?
When oxygen is produced sulphur gas is oxidised to H2SO4 and is rained out as sulphate. Sulphur gasses also undergo photolysis oxidation in the atmosphere. Both of these processes produce a unique pattern
Why do we use iron chemistry?
Iron is oxidised in the presence of oxygen so as oxygen in the atmosphere increases so does the abundance of rust
What are Red beds?
These are the oxygenation of olivine (high in iron) rich soils, so rust red beds of soil are accumulated
How do we use uraninite as a proxy?
Some uranium isotopes are very sensitive and breaks down easily in the presence of oxygen so the lack of uranitite means increased breakdown which means increased
When was the rise of land plants?
The Devonian period
What were the first plants to colonise the land? KEY FEATURES
Bryophytes- Non vascular, no lignin, no specilisation against dessication