2013-10-03. The Mystery of Earth’s Oxygen.

posted Oct 8, 2013, 9:09 AM by Alan Gould
For GSS Life and Climate chapter 5. Excerpt: Donald E. 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.    ...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. ...the atmosphere three billion years ago had only 0.03 percent of today’s oxygen levels. ...some microbes had evolved the ability to carry out photosynthesis.... 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.... In his forthcoming book, “Oxygen: A Four Billion Year History,” Dr. Canfield suggests that this weak vacuum drove a sudden climb in oxygen that geochemists see in rocks from about 2.3 billion years ago. “Now we get to the point where the earth has calmed down enough that the balance has tipped in the favor of oxygen,” he said. ...Reporting last week in The Proceedings of the National Academies of Sciences, Dr. Canfield and his colleagues report that there was so much oxygen in the atmosphere that it penetrated down a thousand feet into the ocean. Dr. Canfield speculates that oxygen may have become as abundant as it is today, at least for a while. ...Life and earth have continued to twiddle the oxygen knob over the past two billion years. When plants evolved, for example, they began storing huge amounts of carbon in wood and other tough tissues, leaving less to react with oxygen and pull it out of the atmosphere. By 300 million years ago, oxygen had risen to levels as high as 50 percent higher than today. But as continents moved across the globe, the planet’s geography came to favor deserts. Forests shrank, bringing down the oxygen levels.... http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html. Carl Zimmer, The New York Times.