The Mystery of Earth’s Oxygen
2013-10-09 0:00

By Carl Zimmer | NYTimes



To Donald E. Canfield, there’s something astonishing in every breath we take. “People take oxygen for granted because it’s just there and we breathe it all the time,” said Dr. Canfield, a geochemist at the University of Southern Denmark. “But we have the only planet we know of anywhere that has oxygen on it.”

What’s even more astonishing is that the earth started out with an oxygen-free atmosphere. It took billions of years before there was enough of it to keep animals like us alive.

Although scientists have been struggling for decades to reconstruct the rise of oxygen, they’re still making fundamental discoveries. In just the past two weeks, for example, Dr. Canfield and his colleagues have published a pair of studies that provide significant clues about some of the most important chapters in oxygen’s history. They’re finding that our weirdly oxygen-rich atmosphere is the result of a complicated dance of geology and biology.

To study the ancient atmosphere, geochemists examine the chemical fingerprints left behind on rocks. Some rocks contain molecules that could have formed only in the presence of oxygen. The more of those molecules geochemists find in a rock, the more oxygen must have been in the atmosphere at the time.

When they look at the oldest rocks on earth, they find no trace of oxygen in the atmosphere. Instead, their research indicates that earth’s primordial air was made up mostly of carbon dioxide, methane and nitrogen. The sun’s rays created some free oxygen by splitting it off from carbon dioxide and other molecules. But the oxygen disappeared almost as soon as it was formed.

That’s because oxygen is an enormously friendly element, forming bonds with a wide range of molecules. It attached to the iron in rocks, for example, creating rust. It joined with hydrogen spewed out from volcanoes to form hydrogen peroxide and other compounds. Our planet, in other words, was a giant oxygen vacuum in its early years.

That changed about three billion years ago. In the Sept. 26 issue of Nature, Dr. Canfield and his colleagues reported the fingerprints of oxygen in rocks from that time period. They estimate that the atmosphere three billion years ago had only 0.03 percent of today’s oxygen levels. That may not sound like much, but it marked a huge shift in the earth’s chemistry.

Sunlight alone couldn’t have put that much oxygen in the atmosphere. Only life could.

By three billion years ago, some microbes had evolved the ability to carry out photosynthesis. Floating at the surface of the ocean, they used energy from sunlight to grow on carbon dioxide and water. They gave off oxygen as waste.

Much of the oxygen released by these photosynthetic microbes was sucked out of the atmosphere by the earth’s vacuum. When microbes died, oxygen reacted with their carbon.

But a tiny amount of oxygen remained behind because some of the organic matter from the dead microbes sank from the surface of the ocean to the sea floor, where oxygen couldn’t react with it. The oxygen remained in the air.

[...]

Read the full article at: nytimes.com




Related Articles
Discoveries of Oxygen
Mars had an oxygen-rich atmosphere four billion years ago
Cosmic Dust --"A Clue to Origin of Earth’s Oxygen and Water?"
World’s oldest fossils: Researchers claim bacteria existed on Earth before OXYGEN


Latest News from our Front Page

Pressure from the United Patriots Front Stops Mosque Plan
2016-04-28 20:10
Pressure from the United Patriots Front appears to have killed off a mosque development in Narre Warren North. The City of Casey council now looks likely to withhold planning approval for the development in a special meeting set for Tuesday night. A council report, to be considered by councillors on Tuesday, recommends that the approval be blocked. The mosque opponents’ cause has been helped by councillor ...
Police face questions over the influence of the Freemasons
2016-04-28 20:48
South Yorkshire Police today face questions over whether powerful 'secret society' the Freemasons held sway over the force at the time of Hillsborough. Families of victims say that officers who were Masons were promoted into powerful positions despite being ill-equipped, including match commander David Duckenfield. Duckenfield told the fresh inquests he had been a Freemason since 1975 and became head of his ...
England Bans its Own Flag to Avoid Offending Muslims
2016-04-27 2:23
St. George's Cross "racist" towards immigrants Government officials said their city was ‘too multicultural’ to celebrate St George’s Day, England’s version of the 4th of July. The council said that displaying the English flag may have been seen as “racist” towards immigrants.
Half of Western European men descended from one Bronze Age ‘king’
2016-04-27 2:09
Half of Western European men are descended from one Bronze Age ‘king’ who sired a dynasty of elite nobles which spread throughout Europe, a new study has shown. The monarch, who lived around 4,000 years ago, is likely to have been one of the earliest chieftains to take power in the continent. He was part of a new order which emerged in ...
"Local Residents" Are Filmed Stealing Dozens of Bottles of Water at London Marathon Stop
2016-04-25 23:10
Editor's Comment: "Local" residents? Why bother blurring their faces? We know who they are. ... London marathon runners were robbed of dozens of bottled waters when thieves raided a refreshment area armed with trolleys during today's race. Nearby residents - including parents with children - were captured on camera piling up crates of free water handed out by volunteers during the 26-mile event. Marathon ...
More News »