The earliest oxygen-breathing bacteria (Evolution)

by dhw, Saturday, October 22, 2011, 13:24 (4589 days ago) @ David Turell

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?