The earliest oxygen-breathing bacteria (Evolution)
by David Turell 
, Saturday, October 22, 2011, 02:38 (4589 days ago)
Estimated at 2.48 billion years ago.
http://www.sciencedaily.com/releases/2011/10/111019181210.htm
The earliest oxygen-breathing bacteria
The research team, led by U of A geomicrobiologist Kurt Konhauser, made their find by investigating a link between atmospheric oxygen levels and rising concentrations of chromium in the rock of ancient seabeds.
"We suggest that the jump in chromium levels was triggered by the oxidation of the mineral pyrite (fool's gold) on land," said Konhauser.
Pyrite oxidation is a simple chemical process driven by two things: bacteria and oxygen. The researchers say this proves that oxygen levels in Earth's atmosphere increased dramatically during that time.
"Aerobic bacteria broke down the pyrite, which released acid that dissolved rocks and soils into a cocktail of metals, including chromium," says Konhauser. "The minerals were then carried to the oceans by the run-off of rain water.
"Our examination of the ancient seabed data shows the chromium levels increased significantly 2.48 billion years ago," said Konhauser. "This gives us a new date for the Great Oxidation Event, the time when the atmosphere first had oxygen."
The rising levels of atmospheric oxygen fostered the development of new bacteria species, and Konhauser says that, following the evolutionary path back to that first oxygen-breathing life form on land, our ancestors started off in a pool of highly acidic water.
The researchers say the modern analogue for that first primitive oxygen-dependent life form on Earth is still with us.
"The same bacterial life forms are alive and well today, living off pyrite and settling in the highly acidic waste waters of mining sites the world over," said Konhauser.
As always, David, I’d like to thank you for keeping us up to date on the latest scientific discoveries. I try very hard to follow these links, as you select items that are highly relevant to our discussions – in this case, evolution – so I hope you’ll forgive me if I continue to ask what may seem like silly questions. Here we are told that aerobic (= oxygen-dependent) bacteria on land broke down the pyrite, and this released acid into the oceans. Why then do the researchers argue that our ancestors started off in acidic water? Why weren’t the preceding oxygen-dependent land bacteria our ancestors?
The earliest oxygen-breathing bacteria
by David Turell , Saturday, October 22, 2011, 23:23 (4588 days ago) @ dhw
Here we are told that aerobic (= oxygen-dependent) bacteria on land broke down the pyrite, and this released acid into the oceans. Why then do the researchers argue that our ancestors started off in acidic water? Why weren’t the preceding oxygen-dependent land bacteria our ancestors?
Not silly. Misunderstood. First were the cyanobacteria which used a metabolism that created some oxygen in the atmosphere, which did not have oxygen at first. Once enough oxygen appeared than organisms could appear that used oxygen. The acidic water is where the researchers found the organism, presently. they think it needed the water and never changed.
The earliest oxygen-breathing bacteria
Dhw: We are told that aerobic (= oxygen-dependent) bacteria on land broke down the pyrite, and this released acid into the oceans. Why then do the researchers argue that our ancestors started off in acidic water? Why weren’t the preceding oxygen-dependent land bacteria our ancestors?
DAVID: Not silly. Misunderstood. First were the cyanobacteria which used a metabolism that created some oxygen in the atmosphere, which did not have oxygen at first. Once enough oxygen appeared than organisms could appear that used oxygen. The acidic water is where the researchers found the organism, presently. they think it needed the water and never changed.
Thank you for this explanation, but may I try your patience just a little further? The researchers expressly talk of aerobic bacteria (= organisms that used oxygen) breaking down the pyrite on land, so their oxygen-dependency PRECEDED that of the bacteria in the acidic water. Konhauser, however, says the water-based bacteria constituted the “first primitive oxygen-dependent life formâ€, and “our ancestors started off in a pool of highly acidic waterâ€. The water didn’t become highly acidic until land-based bacteria that were ALREADY oxygen-dependent had broken down the pyrite, in which case I still don't understand why they weren’t the ancestors that started us off. Apologies if I’m being obtuse, and I promise not to badger you with this again!
The earliest oxygen-breathing bacteria
by David Turell , Sunday, October 23, 2011, 20:08 (4587 days ago) @ dhw
Konhauser, however, says the water-based bacteria constituted the “first primitive oxygen-dependent life formâ€, and “our ancestors started off in a pool of highly acidic waterâ€. The water didn’t become highly acidic until land-based bacteria that were ALREADY oxygen-dependent had broken down the pyrite, in which case I still don't understand why they weren’t the ancestors that started us off. Apologies if I’m being obtuse, and I promise not to badger you with this again!
If the atmosphere had no oxygen or a tiny amount we must assume that organisms could use only what was present and that was not oxygen. These organisms were not oxygen dependent. When there was a substantial increase in oxygen then some organisms could mutate and use oxygen. Oxygen is an extremely caustic and dangerous substance. Think of rusting iron tools; we consume anti-oxidents to protect our bodies. Our bodies use oxygen with many protections. Those pyrite organisms had to carefully adapt to oxygen. At the same time those pyrite eaters acidified the water. That is what they do today. In brief, image that several factors are changing at once, and bit by bit as oxygen became more and more available from oxygen producing organisms, more and more organisms learned to use oxygen. That is the best explanation I can give. Remember, first no oxygen, then a gradual increase. The environment we have today developed bit by bit.
The earliest oxygen-breathing bacteria
by romansh 
, Sunday, October 23, 2011, 23:33 (4587 days ago) @ David Turell
My guess would be the early atmosphere would have been fairly reducing, SO2 and methane. So any early oxygen produced would have been mopped up. Only once the reducing character of the atmosphere had been "neutralized", only then could any significant increase in oxygen content be observed.
The earliest oxygen-breathing bacteria
by David Turell , Monday, October 24, 2011, 01:03 (4587 days ago) @ romansh
My guess would be the early atmosphere would have been fairly reducing, SO2 and methane. So any early oxygen produced would have been mopped up. Only once the reducing character of the atmosphere had been "neutralized", only then could any significant increase in oxygen content be observed.
Exactly right. I don't remember the currently proposed mixture of the early atmosphere but it has been definitely shown that the Urey-miller 'lightning in a bottle' atmosphere mixture they used was wrong.