5. The great oxygenation event Flashcards
What does the red colour in red sandstone show?
A presence of oxygen at the time of formation
What’s the difference between Ferric iron and Ferrous iron?
Ferrous iron is reduced and greyish in colour.
Ferric iron is oxidised and reddish in colour
What is the significance of ferric iron (rust) being insoluble)?
It can form a protective layer for some time
What is the significance of red sandstones?
Red beds trace the great oxygenation event by showing when the atmosphere they were deposited in became oxygen rich
When do red sandstone beds start appearing?
Approx 2.3Bya
What other evidence is there for the time of the great oxygenation event other than red beds?
Disappearance of uranium, oxidised Mn, disappearance of BIFs
Why does the relationship between methane and oxygen make it hard to figure out how oxygen built up to current levels?
Almost all oxygen in the atmosphere would combine with methane under UV light to produce water and CO2 that enter the ocean.
What is the present percentage concentration of oxygen in our atmosphere?
21%
What was necessary for the ozone layer to form?
A fairly high concentration of oxygen
What are the four possibilities for oxygen and methane swapping places?
(one being trace and one being rich in the atmosphere)
-Spread of oxygenated photosynthesis to somewhere this wouldn’t also create methane.
- Big sustained pulse of carbon burial.
- Lower volcanic input of reduced compounds to be oxidised.
- Loss of reduced material from the planet (atmospheric escape)
When did the Great Oxygenation Event take place?
2.4Bya to 2.0Bya approx
What is methanogenesis?
The formation of methane from microbes called methanogens
For how many millions of years has there been much more oxygen in the atmosphere?
approx 540
(around the time of the cambrian explosion)
At what percentage of atmospheric oxygen did the Big Blush happen?
1%
What are palaeosols?
Old soils
