Early date for 'oxygen-rich' earth
Updated on 27 September 2007
Scientists have discovered evidence of oxygen pulsing through the Earth's atmosphere at least 50 million years before it was thought to have first been present.
Until now, scholars thought that the Great Oxidation Event (GEO), which began about 2.45 billion years ago, marked the transition from an oxygen-poor to an oxygen-rich atmosphere.
But new research by two teams of scientists, published in the journal Science, challenges the notion that levels of oxygen were negligible before this shift.
Ariel Anbar, a biogeochemist who led the research team at Arizona State University in America, said the finding was "unexpected".
He said: "We seem to have captured a piece of time before the GOE during which the amount of oxygen was actually changing - caught in the act, as it were."
Before now, little was known of environmental changes prior to the GOE.
It was thought that for the first half of the Earth's 4.56-billion-year history, the environment held almost no oxygen, other than bound to hydrogen in water or to silicon and other elements in rocks.
But this new evidence of oxygen about 2.5 billion years ago strengthens the notion that organisms learned to produce the element long before the GOE, and that its rise in the atmosphere was ultimately controlled by geological processes.
The discovery was made by analysing layers of a core sample of sedimentary rock, 908 metres long, from the Hamersley Basin in Western Australia - one of the few places where it is possible to find unaltered rock formed in the first half of the Earth's history.
The two research teams were led by geologists from the University of Maryland and Arizona State University.
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