Geologists rice University in the USA explained what caused the Oxygen catastrophe or the “Great oxygen event” 2.5 billion years ago, when the Earth’s atmosphere has changed dramatically, and saturated with oxygen is important for respiration and the emergence of complex life. Although this was considered to be photosynthetic bacteria, their activity is not able to explain some other geochemical peculiarities of the time. About it reported in a press release on Phys.org.
Researchers have proposed the theory that the cause of the accumulation of oxygen steel tectonic processes, not biological. Although photosynthetic cyanobacteria are considered to be the main supplier of oxygen in the atmosphere, they appeared over 500 million years before the Oxygen catastrophe. Have been proposed various hypotheses to explain why the oxygen needed so much time to accumulate. At the same time they do not take into account “event Lomagundi” — a marked change in the ratio of carbon isotopes in carbonate rocks, which began 100 million years after the “Great oxygen event”.
Before and after Lomagundi the ratio of the isotope carbon-13 and carbon-12 was 1 to 99, but during this period, the content of carbon-13 increased by 10 percent. The reason for this phenomenon was also believed to be cyanobacteria, since these microorganisms prefer to consume carbon-12, and deposits formed by the remains of micro-organisms and depleted in carbon-13.
According to scientists, and the Oxygen catastrophe, and Lomagundi occurred due to a sharp increase in tectonic activity, which led to the emergence of a large number of volcanoes spewing carbon dioxide into the atmosphere. The climate became warmer, and a large amount of precipitation strengthened the processes of weathering of minerals on land. Contained in the effluent of the carbon was in the oceans, which caused a boom in the growth of cyanobacteria and the accumulation of carbonates. At the same time, this same process contributed to the accumulation of oxygen in the atmosphere.
In the next phase of organic and inorganic carbon on the ocean floor sank into the mantle in subduction zones, where oceanic plate dives under the continental and melts. Inorganic carbon in the composition of the carbonates is released quickly in the form of volatile gases through volcanoes, and organic — using hundreds of millions of years.
Event Lomagundi occurred when the carbon-13 of carbonate returned to the surface of the Earth, and ended when it was the turn of carbon-12. These carbon dioxide emissions was important to the spread of life.
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