oxygen appeared in Earth’s atmosphere for 3 billion years ago
text: Alexander Temples / Infox.ru
published Sept. 25 ’13 23:17
Source: fotobank.ru
Geologists have determined that the oxygen present in the atmosphere of the Earth most of its history. Therefore, the first photosynthetic organisms arose much earlier than is commonly believed.
This is stated in the article Danish researchers from the University of Copenhagen, published in a recent issue of the journal Nature.
is estimated that nearly half of its 4.5-billion stories Land held without oxygen atmosphere. For the first time in a tangible amount of oxygen appeared on Earth during the so-called revolution of oxygen about 2.3 billion years ago – it began to allocate photosynthetic bacteria. On increasing the concentration of oxygen speak oxidized species in the period for the first time appear in the fossil record.
However, the authors found that oxygen was fed to atmosphere at 700 million years earlier. This is evidenced by the analysis of samples paleopochvy age 3 billion years old, collected in South Africa. The scientists found that the observed reduction in paleosol isotope content of chromium-53. This shows the active oxidation processes in which the valency chromium in chromium III passed the valency IV.
fact that chromium-53 accumulates predominantly in the oxide form, and then washed IV chromium compound that reduces the total content of the isotope. Based on the characteristics of this process, geologists have calculated that 3 billion years ago, the concentration of oxygen in the atmosphere was 3 for 10 in the minus fourth degree of current levels. Almost certainly he had a biogenic origin, as a result of purely abiotic processes as much O2 can not be formed.
«Our study shows that aerobic forms of life and photosynthesis, in which oxygen is liberated, appeared very early,” – said Sean Crowe, one of the authors of the work.
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