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> [i]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&apos;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&apos;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.[/i]
> 
> As always, David, Iâ€™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 â€“ in this case, evolution â€“ so I hope youâ€™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 werenâ€™t the preceding oxygen-dependent land bacteria our ancestors?