05. Oxygen

The Origin of Our Oxygen-Rich Atmosphere

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

2012 Mar 18.  Archaean Haze  |  Nature Geoscience Press Release.  Excerpt: The Earth's atmosphere periodically transitioned between a hydrocarbon haze and haze-free conditions 2.65–2.5 billion years ago, reports a paper published online this week in Nature Geoscience. The haze permanently retreated following the oxygenation of the atmosphere approximately 100 million years later…. (See also: http://newswatch.nationalgeographic.com/2012/03/19/early-earth-turned-methane-haze-on-and-off/)

2009 March 25. Deep-sea Rocks Point To Early Oxygen On Earth. Science Daily. Excerpt: Red jasper cored from layers 3.46 billion years old suggests that not only did the oceans contain abundant oxygen then, but that the atmosphere was as oxygen rich as it is today, according to geologists.
This jasper or hematite-rich chert formed in ways similar to the way this rock forms around hydrothermal vents in the deep oceans today.
...The researchers drilled diagonally into the base of a hill in the Pilbara Craton in northwest Western Australia to obtain samples of jasper that could not have been exposed to the atmosphere or water. These jaspers could be dated to 3.46 billion years ago.
"Everyone agrees that this jasper is 3.46 billion years old," said Hiroshi Ohmoto, professor of geochemistry, Penn State. "If hematite were formed by the oxidation of siderite at any time, the hematite would be found on the outside of the siderite, but it is found inside," he reported in a recent issue of Nature Geoscience.
...said Ohmoto, "It also means that there was oxygen in the atmosphere 3.46 billion years ago, because the only mechanism for oxygen to exist in the deep oceans is for there to be oxygen in the atmosphere."
In fact, the researchers suggest that to have sufficient oxygen at depth, there had to be as much oxygen in the atmosphere 3.46 billion years ago as there is in today's atmosphere. To have this amount of oxygen, the Earth must have had oxygen producing organisms like cyanobacteria actively producing it, placing these organisms much earlier in Earth's history than previously thought....

27 September 2007 NASA RELEASE: 07-215 - NASA RESEARCH INDICATES OXYGEN ON EARTH 2.5 BILLION YEARS AGO. Excerpt: MOFFETT FIELD, Ca lif. - NASA-funded astrobiologists have found evidence of oxygen present in Earth's atmosphere earlier than previously known, pushing back the timeline for the rise of oxygen in the atmosphere. Two teams of researchers report that traces of oxygen appeared in Earth's atmosphere from 50 to 100 million years before what is known as the Great Oxidation Event. This event happened between 2.3 and 2.4 billion years ago, when many scientists think atmospheric oxygen increased significantly from the existing very low levels.
Scientists analyzed a kilometer-long drill core from Western Australia, representing the time just before the major rise of atmospheric oxygen. They found evidence that a small but significant amount of oxygen was present in Earth's oceans and atmosphere 2.5 billion years ago. The findings appear in a pair of research papers in the Sept. 28 issue of the journal Science.
"We seem to have captured a piece of time during which the amount of oxygen was actually changing -- caught in the act, as it were," said Ariel Anbar, an associate professor at Arizona State University, Tempe, and leader of one of the research teams.
...One possible explanation for the Great Oxidation Event is the ancient ancestors of today's plants first began to produce oxygen by photosynthesis. However, many geoscientists think organisms began to produce oxygen much earlier, but the oxygen was destroyed in reactions with volcanic gases and rocks.
..."What we have now is new evidence for some oxygen in the environment 50 to 100 million years before the big rise of oxygen," Anbar said. "Our findings strengthen the notion that organisms learned to produce oxygen long before the Great Oxidation Event, and that the rise of oxygen in the atmosphere ultimately was controlled by geological processes."
...For more information about the NASA Astrobiology Institute, visit:
http://nai.nasa.gov

3 February 2004. When Giants Had Wings and 6 Legs. By HENRY FOUNTAIN, New York Times. Before the dinosaurs, it was the insects that were huge. Why? It may have been the air.... There was an array of giant flightless insects, and a five-foot-long millipede-like creature, Arthropleura, that resembled a tire tread rolled out flat. But perhaps the most remarkable of all were the giant dragonflies, Meganeuropsis permiana and its cousins, with wingspans that reached two and a half feet. They were the largest insects that ever lived. These large species thrived about 300 million years ago, when much of the land was lush and tropical and there was an explosion of vascular plants (which later formed coal, which is why the period is called the Carboniferous). But the giant species were gone by the middle to late Permian, some 50 million years later. Scientists have long suspected that atmospheric oxygen played a central role in both the rise and fall of these organisms. Recent research on the ancient climate by Dr. Robert A. Berner, a Yale geologist, and others reinforces the idea of a rise in oxygen concentration - to about 35 percent, compared with 21 percent now - during the Carboniferous. Because of the way many arthropods get their oxygen, directly through tiny air tubes that branch through their tissues rather than indirectly through blood, higher levels of the gas might have allowed bigger bugs to evolve.... "It's been out there in the literature for a long time without a causal mechanism," said Dr. Robert Dudley, a professor at the University of California at Berkeley who has studied the effects of elevated oxygen pressures on modern insects. ...Dr. Jon F. Harrison, a professor at Arizona State ... said, "It's still in the realm of speculation."


 

Comments