Oxygen-breathing bacteria may have lived on land 100 million years sooner than previously thought.

Researchers from the New University of Alberta revealed that they have evidence that oxygen-breathing bacteria had lived on land 2.48 billion years ago, which is nearly 100 million years earlier than scientists had originally theorized.

Geomicrobiologist Kurt Konhauser, who led the team of researchers, analyzed the link between rising atmospheric oxygen levels and rising concentration of chromium in the ancient sea beds. The team believes the jump in chromium levels is a direct result of the land-based bacteria's oxidization of the mineral pyrite.

Bacterial oxidation of pyrite could only have occurred if there was enough oxygen in the Earth's atmosphere. Pyrite oxidation needs bacteria and oxygen to occur. Aerobic bacteria would break down the pyrite which will release acid.

The acid dissolves rocks and soils into metals including chromium, which would be transferred to the ocean by rainwater and this accounted for jump in chromium levels in the sea bed. The date for the chromium levels in marine sedimentary rock was about 2.48 billion years ago.

"This gives us a new date for the Great Oxidation Event, the time when the atmosphere first had oxygen," said Konhauser. "The rising levels of atmospheric oxygen fostered the evolution of new bacteria species that survived by aerobic respiration on land.

"Our ancestors started off in an acid bath as oxygen-breathing bacteria."

Konhauser had been involved in previous studies about prehistoric Earth, including the theory that the "Great Oxidation Event" started because the sea ran low on nickel. Konhauser had proposed that a lack of nickel starved the methane-producing bacteria called methanogens. Because the methanogens starved there was a gradual decline in atmospheric methane, spurring the growth of cyanobacteria, which produce oxygen.

The research by Konhauser and his team was published in Wednesday's edition of the scientific journal Nature.