Saturday, September 29, 2007

O2 is millions of years old

WASHINGTON: Oxygen, key to life on Earth today, began to appear on the planet millions of years earlier than scientists had thought, new research indicates.

An analysis of a deep rock core from Australia indicates the presence of at least some oxygen 50 million to 100 million years before the great change when the life-giving element began rising to today’s levels, according to two papers appearing in Friday’s edition of the journal Science .

Previously, the earliest indications of oxygen had been from between 2.3 billion and 2.4 billion years ago when the "Great Oxidation Event" occurred.

The cause of the event is still not known, but before that the atmosphere was dominated by methane and ammonia. Today oxygen makes up about 21% of the atmosphere.

The discovery of traces of early oxygen was made in a study of a 3,000-foot-long rock core extracted in western Australia.

"We seem to have captured a piece of time before the Great Oxidation Event during which the amount of oxygen was actually changing — caught in the act, as it were," Ariel Anbar, an associate professor in Arizona State University’s school of earth and space exploration, said in a statement.

"We couldn’t exist in a world that didn’t have a lot of oxygen in the atmosphere. So understanding how that came to be is fundamental in understanding how it is the Earth came to be a planet that is hospitable to us," said Anbar.

The two research teams were led by Alan Jay Kaufman, associate professor of geochemistry at the University of Maryland and Anbar. Carl Pilcher of the Nasa Astrobiology Institute said: "Studying the dynamics that gave rise to the presence of oxygen in Earth’s atmosphere deepens our appreciation of the complex interaction between biology and geochemistry. Their results support the idea that our planet and the life on it evolved together."

Earth is roughly 4.5 billion years old. For about the first half of the planet’s existence, the environment held almost no oxygen, other than bound to hydrogen in water or to silicon and other elements in rocks.

Then, during this crucial period, oxygen started appearing in the atmosphere and oceans. But it still made up much less than 1% of the atmosphere. "It’s not as if oxygen then rises all the way up to the modern level. It takes another billion years or more before it gets to the modern level. We transition from a world where there’s very little to a world where there’s a good amount," Anbar added.

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