Lecture 26: Proterozoic Biosphere Flashcards
What years did the Proterozoic era span?
Between 2.5 billion and 540 million
How long ago did the Great Oxidation event occur?
2.5 Billion years ago
What was the Great Oxidation event?
A period in time when the atmosphere accumulated oxygen
What was the composition of the atmosphere before the great oxidation?
N2, CO2 and Methane
What gives evidence for early life?
- Stromatolites
- Microfossils
- Isotopes
Why are sulfur isotopes able to tell us about the atmosphere?
Because organisms tend to fractionate these isotopes which are measurable and then tell us about the atmosphere
How is Pyrite affected by the presence of oxygen?
It forms sulfuric acid
How does sulfur evidence of the great oxidation event?
Fractionation of sulfur in by bacteria tells us that there was oxygen from pyrite that went into the ocean which tells us there was oxygen in the atmosphere
How is 33 sulfur produced?
The lack of oxygen in the atmosphere causes a lack of Ozone which is affected by fluxes in UV
How is 33 Sulfur evidence for the great oxidation event?
The levels of 33 sulfur dropped after the great oxidation event meaning that ozone existed due to the lack of UV rays
What is a Red Bed?
Iron oxide that precipitated onto other things
How do Red Beds tell us there is oxygen in the atmosphere?
Because the iron in the ocean would not precipitate out unless there is oxygen in the atmosphere
How do Red breds provide evidence of the Great Oxygenation Event?
When iron precipitates out of oceans, atmospheric oxygen is needed, telling us that oxygen was available in the atmosphere
What does increase roundness of a rock mean?
The more its been transported
How do rounded pyrite grains tell us about the Great Oxidation event?
Rounded pyrite grains mean that there was no oxygen in the atmosphere because if there was oxygen in the atmosphere it would have oxidized the pyrite
How does Manganese tell us about the great oxidation event?
Finding layers of manganese oxide tells us that there was oxygen in the atmosphere
How many years does it take to fully oxidate the planet?
About 200 million years
Through what period did the great oxidation event occur?
2.5 - 2.3 billion years
How many years ago did banded iron formations form?
3.8 billion years ago to 1.8 billion years ago
What kind of sediments are Banded Iron Formations?
Chemical sediments with no sand, silt or clay just iron oxide
What metal is rust?
Ferrihydrite Fe(OH)3
What are the two ways that BIFs are proposed to develop?
One method is through oxygenic photosynthesis of plankton and the other is through oxygen photosynthesis producing ferrihydrite
What is the process of ferrihydrite development driven by?
Biological processes
What are the two oxidation states of Chromium?
The reduced phase and the oxidized phase
