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Washington, July 10 The Earth 's oxygen levels have increased and decreased more than a hundred million years before the global success of the Great Oxidation Event, there are about 2 , 4 billion years, according to a study.
in the journal Proceedings of the National Academy of Sciences, may have implications in the search for life beyond the Earth.
The coming years will bring new powerful telescopes based on the ground and space able to badyze the atmospheres of distant planets.
The work could help prevent astronomers from unduly excluding "false negatives", or inhabited planets that might not appear to be due to undetectable levels of oxygen, according to them
" The production and destruction of oxygen. in the ocean and the atmosphere over time was a war without evidence of a clear winner, up to the great oxidation, "said Matt Koehler, a Ph.D. student at the University of Washington in the United States.
The Great Oxidation The event was the biologically induced onset of oxygen in the Earth's atmosphere about 2.45 billion years ago.
"These transient oxygenation events were battles in the war, when the scales leaned more in favor of oxygenation.The researchers confirmed the appearance of oxygen in the pbaded from Earth, there are about 150 million years – about 2.66 billion years – and lasted less than 50 million years
. "The isotopes of the Nitrogen tell the story of oxygenation of the ocean surface, and this oxygenation extends over hundreds of kilometers across a marine basin and lasts for less than 50 years. Millions of years ago, "said Koehler.
The team badyzed drill samples taken by Roger Buick, a professor at the University of Washington, in 2012 at another site in the north-west. West of Weste The researchers drilled two cores about 300 kilometers from each other, but through the same rocks. editorial – one core sampled sediments deposited in shallower waters and the other sediment taken from deeper waters
in rock shows, Buick said, a "stepwise change" of the isotopes of the "Nitrogen" and then back to zero. "This can only be interpreted to mean that there is oxygen in the environment. "The isotopes of nitrogen reveal the activity of certain marine microorganisms that use oxygen to form nitrate, as well as other microorganisms that use this nitrate as a source of nitrogen." Energy "
. Nitrogen isotopes sample the surface of the ocean, while selenium suggests oxygen in the air of the ancient Earth.Koehler says that the "ocean" is the same. deep ocean was probably anoxic, or without oxygen, at the time.
The team found abundant selenium in the shallow hole only, that is, it comes from neighboring lands and does not reach deep water.
Selenium is retained in sulphide minerals on land: a greater amount of atmospheric oxygen would result in a greater amount of selenium from the rocks, "and transported to the sea, said Buick.
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