Week 6

Question 1

What is the earliest evidence of photosynthesis?

Answer 1

Bubble being produced in stromatolites
The vertical growth of stromatolites is evidence of cyanobacteria reaching for the photic zone

Question 2

What are three sources of evidence for oxygen proxies?

Answer 2

Mass independent fractionation of sulphur isotopes
Iron redox geochemistry
Uraninite

Question 3

What is MIF of sulphur isotopes?

Answer 3

This is the separation of a mix of isotopes into their unique isotopes.
The ratio of isotopes works as a geochemical proxy

Question 4

What does MIF tell us?

Answer 4

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

Question 5

Why do we use iron chemistry?

Answer 5

Iron is oxidised in the presence of oxygen so as oxygen in the atmosphere increases so does the abundance of rust

Question 6

What are Red beds?

Answer 6

These are the oxygenation of olivine (high in iron) rich soils, so rust red beds of soil are accumulated

Question 7

How do we use uraninite as a proxy?

Answer 7

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

Question 8

When was the rise of land plants?

Answer 8

The Devonian period

Question 9

What were the first plants to colonise the land? KEY FEATURES

Answer 9

Bryophytes-
Non vascular, no lignin, no specilisation against dessication