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Natural Science Forum / Biology / Paleontology / October 2004Extinction of anaerobes / rise of aerobic organisms
My notes suggest that the earliest photosynthesis was around ~3.1 BYA, which concurrently began to create an oxidized atmosphere. This in turn started the extinction of anaerobes and the rise of aerobic organisms. If these notes are relatively accurate, do we have an ballpark idea of the length of time it took for the extinction of anaerobic organisms? (e.g. tens or hundreds of millions of years?) Regards, Brett Aubrey. > My notes suggest that the earliest photosynthesis was around ~3.1 BYA, > which concurrently began to create an oxidized atmosphere. This in turn [quoted text clipped - 3 lines] > the length of time it took for the extinction of anaerobic organisms? > (e.g. tens or hundreds of millions of years?) Regards, Brett Aubrey. Anaerobes didn't become extinct. They were merely forced out of environments that contain free oxygen. Some anaerobes were able to evolve defenses against oxygen. And some of these defenses eventually evolved into the ability to get energy from oxygen. Presumably this was gradual, but I would have no idea how you would go about determining the time scale. >> My notes suggest that the earliest photosynthesis was around ~3.1 BYA, >> which concurrently began to create an oxidized atmosphere. This in turn [quoted text clipped - 10 lines] > but I would have no idea how you would go about determining the time > scale. Try finding out how long it took for enough free oxygen to show up to remove the huge amount of iron disolved in the ocean. I don't recall what the number is but that should be about what your answer is. >>>My notes suggest that the earliest photosynthesis was around ~3.1 BYA, >>>which concurrently began to create an oxidized atmosphere. This in turn [quoted text clipped - 14 lines] > the huge amount of iron disolved in the ocean. I don't recall what the > number is but that should be about what your answer is. No, that just tells you the time it took for photosynthesizers to change the nature of the atmosphere. There could be quite a long period after that in which nobody was taking advantage of all the free oxygen that was newly available, and we would have no way of knowing. >My notes suggest that the earliest photosynthesis was around ~3.1 BYA, >which concurrently began to create an oxidized atmosphere. This in turn [quoted text clipped - 3 lines] >the length of time it took for the extinction of anaerobic organisms? >(e.g. tens or hundreds of millions of years?) Regards, Brett Aubrey. I should check my notes, but from memory, I think that it is generally believed that the generation of free oxygen from photosynthesis did not oxygenate the atmosphere to any great extent until enough Oxygen was generated to fix enormous amounts of iron dissolved in the early oceans. For several billion years, any Oxygen generated was pretty immediately locked up as Iron oxides in massive Banded Iron Deposits. As I recall, there is some uncertainty and controversy about when and how the transition to the modern Oxygenated atmosphere finally took place. A number that sticks in my mind is that the BIFs (Banded Iron Formations) are estimated to contain roughly 20 times the amount of Oxygen found in the modern atmosphere. See http://en.wikipedia.org/wiki/Paleoclimatology and keep in mind that some of what you read there may be controversial. |
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