Lecture 2/7/13 Flashcards
Why is learning about crown groups and stem groups important?
Can shed light on what the ancestral state might be.
How would you track cyanobacterial evolution?
Look for when oxygen came to be
which would tell us when the water oxidizing complex first evolved
How was the rise of O2 found?
In an anoxygenic atmosphere, the interaction between UV light and SO2 would produce small changed in the sulfur isotopes. These would then precipitate to the sediment.
In oxygenic environment, these small changes would disappear because it would get oxidized.
What is MIF? What causes it?
MIF is mass-independent fractionation. It is caused the sulfur precipitation in the rain makes it into the geologic record with these small isotopic of sulfur.
Why is MIF important?
Because MIF can be measured and if we measure the different isotopes of sulfur for rocks of different ages, we can find out when MIF stopped. That is when we had to have our first oxygen. And the WOC would have evolved.
What is the banded iron formation? What is the incorrect belief that a lot of people have?
BIF is a terrible way to record the rise of oxygen (through the “oxidation” of the ocean). It is not layers but rather little lenses. It is a rock that contains more than 10% iron and 40% silica. They tend to look layered.
Why is the belief that BIF shows the primary oxidation state of the ocean wrong? What does it mean?
1 - Ocean does not circulate that way
2 - Iron formation deposits are not layered clearly
3 - Aren’t bands but lenses. Which records the oxidative state of the sediment NOT the ocean.
Means that the varying redox state occurs because of things that have happened to the sediment after it was deposited.
What does BIF actually tell us?
Iron formation actually records the interaction between bacteria and dissolved silica in the environment.
Bac use iron as e- donor and make iron oxyhydroxides. When they die, they produce iron with diff redox states.
