Gold's mine of early information

September 12, 1997

Agricultural policy, smart salmon and sex-change chickens at the British Association's annual festival of science in Leeds

The early atmosphere could have contained much greater concentrations of oxygen than previously thought, says a Leeds University researcher, writes Julia Hinde.

Andrew Barnicoat has spent the past four years working in the Wi****ersrand Basin in South Africa on the world's largest gold mine. The conventional view was that the gold was deposited from cold water containing sand as it flowed into the basin. But Dr Barnicoat's research suggests the gold was deposited later.

He says the gold was carried to the area dissolved in hot water, which ran through cracks in the rocks, which in turn furred up with deposits including gold.

Uranium minerals were also found. These, says Dr Barnicoat, were deposited with the gold, not as grains, but from solution as it passed along the cracks. "The traditional model envisages uranium deposited like particles of sand. For that to happen there has to be no oxygen in the air or the uranium would have dissolved.

"We can show it was deposited from solution, not as grains. This removes a significant piece of evidence that was previously used to suggest low oxygen levels in the early environment. In fact, to get the uranium into solution would require oxygen.

"We suggest there was more oxygen in the atmosphere than the vanishingly small fraction normally proposed. It could have been 1 or 2 per cent of the atmosphere or more."

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