Newspaper article The Christian Science Monitor

Surprise: Earth Had Oxygen before Great Oxidation Event

Newspaper article The Christian Science Monitor

Surprise: Earth Had Oxygen before Great Oxidation Event

Article excerpt

Earth, it now unfolds, had substantial levels of oxygen about 600 million years earlier than thought.

Findings published this week in Nature suggest that the Earth's atmosphere was, if not quite oxygen rich, already somewhat oxygenated about 3 billion years ago. That revises previous timelines of our planet, which had put the first rumblings of oxygenation about 2.3 billion years ago, at the beginning of what is known at as the Great Oxidation Event.

"Instead of a simple two-stage Early Earth model with anoxic atmosphere prior to 2.4 billion years ago and oxic conditions ever after, we had at least 600 million years long transition phase," says Michael Bau, a geoscience professor at Jacobs University, in Germany, and an author on the paper.

The tale of Earth's oxidization is often told like this: For the first two billion years of Earth's existence, the mottled, volcano- pocked planet had little oxygen - about 0.00001 percent of current levels. But, about 2.3 billion years ago, there was a dramatic change. In what was perhaps the happiest moment in Earth's existence, photosynthesizing bacteria enjoying the sunlight began, in an unusually productive feat for sunbathers, to process it into oxygen.

It was, so far as we know, a moment unlike any other in the universe. While Mars, just 60 million years older than Earth, browned and reddened, Earth was furnished in greens and blues and, later, in all the brilliant colors that decorate its plants and animals and all the protists in-between. The modern Earth owes about 85 percent of its oxygen to phytoplankton, beginning with the cyanobacteria - blue-green algae - that first quilted the planet those billions of years ago.

But a team of researchers has now posed the question: What if the oxygenation of Earth began not with a moment, but with a long, transition phase?

The researchers assessed the distribution of two chromium isotopes, Chromium-53 and Chromium-52, in 3-billion-year-old sediment in South Africa's Kwazulu-Natal Province. …

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