Great Oxygenation Event

Amidst the Great called oxygen catastrophe, even oxygen crisis or Great Oxygenation event ( GOE ), refers to the appearance of free oxygen ( dioxygen, O2) in the waters of the earth and in the atmosphere, which was toxic to the former anaerobic organisms. In the development of the Earth's atmosphere, it represents the transition from the second to the third atmosphere dar. This essential, caused by living organisms environmental change took place before about 2.4 billion years ago. She was overcome by adaptations of organisms to the presence of oxygen.

Expiration

The first atmosphere contained free oxygen (O2) at most in very low concentrations. Developed before probably about 3.8 billion years ago, microorganisms, according to current knowledge cyanobacteria from a simpler photosynthesis form a new one, in which, in contrast to the older form of O2 is produced as a waste product and is therefore called oxygenic photosynthesis. This O2 was formed in considerable quantities in the oceans, both before and after the GOE. However, there was a significant difference: Before the GOE, the oxygen formed in the oxidation of organic substances, hydrogen sulfide and dissolved iron was completely consumed ( as divalent iron ion Fe2 present). The GOE was the time at which these substances, especially Fe2 , were largely oxidized and the new entry of these substances could not fully use up the oxygen formed. The excess free oxygen began now in seawater and accumulate in the atmosphere.

It is believed the majority of that between the occurrence of oxygenic photosynthesis with the associated production of O2 and the beginning of the accumulation of free oxygen was a long time, because large amounts of oxidizable substances with O2 were available and replenished from weathering and volcanism, the O2 formed was so consumed immediately.

The oxidation of Fe2 to trivalent iron ions Fe3 resulted in the deposition of Bändererz ( Banded Iron Formation), where iron is present mainly in the form of oxides, namely hematite Fe2O3 and magnetite Fe3O4. In ancient continent shields that have been changed in a long time relatively little tectonic, such Bändererze exist today, for example, Hamersley Basin, Western Australia, Transvaal Craton, South Africa, Animikie group in Minnesota. They are globally the most important iron ore. Oxygen began shortly ( about 50 million years) to remain in the atmosphere before the GOE.

Theory of the late appearance of oxygenic photosynthesis

According to this theory, the phototrophic producers of oxygen developed until just before the major rise in atmospheric oxygen concentration. The theory is based on the mass -independent fractionation of sulfur isotopes, which is ascribed to an indicator function for oxygen. In this theory, the time between the evolution of photosynthetic oxygen microorganisms and the time of the O2 concentration increase must not be explained.

However, there is the possibility that the oxygen indicator has been misinterpreted. In the course of the proposed time lag of the above theory, a change from mass- independent fractionation ( MIF ) to a mass-dependent fractionation ( MDF) of sulfur took place. It is believed that this was the result of the appearance of the oxygen O2 in the atmosphere. Oxygen would have inhibited the MIF -causing photolysis of sulfur dioxide. This change of MIF to the MDF sulfur isotopes could also be caused by an increase of glacial weathering. Also in question is a Homogenierung the marine sulfur deposits as a result of an increased temperature gradient during the Huron icing.

Lag theory

( Could be up to 900 million years) under the follow-up refers to the time lag between the time at which the oxygen production of photosynthetic organisms started and the rapid increase ( quickly in geological time ) atmospheric oxygen prior to about 2.5 to 2.4 billion years. With the help of a series of hypotheses attempting to explain this time lag.

Tectonic trigger

According to this theory, the time offset is explained by the increase of oxygen had to wait for tectonically induced changes in the " anatomy " of the earth. It was the appearance of shelf seas where reduced carbon reaching the sediments and could be deposited there. In addition, the newly produced oxygen was first used in different oxidation in the ocean, in the first place in an oxidation of ferrous iron. For this phenomenon, there is evidence in older rock formations, namely large amounts Bändererze, who had apparently been deposited by the iron oxidation. Bändererze make the most of the commercially degradable iron ores.

Nickel deficiency

Chemosynthetic organisms were a methane source. However, methane was the case of molecular oxygen, for oxygen oxidation of methane in the presence of UV radiation, without any further action to carbon dioxide and water. Today methanogenic microbes need to nickel as a coenzyme. When cooled the earth's crust, the nickel supply and thus the methane production was reduced, which allowed that oxygen dominated the atmosphere. In the period 2.7 to 2.4 billion years ago today, the deposited amount of nickel declined steadily; it was originally at 400 times the present level.

Bistability

Published in 2006 Bistabilitäts theory tries to explain the 300- millions of years of time offset using a mathematical model atmospheres. Here takes account of the fact that a UV - shielding reduces the methane oxidation as soon as the oxygen content is high enough to permit the formation of the ozone layer. In the explanation, two stable states are adopted: in a state of the atmosphere containing 0.02 % of oxygen, in other much more (21% or more). Oxygen disaster can be considered as the point when it was switched between these two states.

Follow the GOE

The increasing oxygen content in the oceans may have wiped out a large portion of obligate anaerobic organisms that populated the earth at this time. Electricity produced by cyanobacteria in oxygenic photosynthesis oxygen was deadly and much more likely responsible for the largest mass extinction of obligate anaerobic organisms. When not matched to O2 beings are formed in the course of their metabolism peroxides which are highly reactive and can damage vital components of living things. Probably developed organisms during the time when despite forming O2, but was always consumed in oxidation reactions, enzymes ( peroxidases ), which destroy the forming peroxides, so that the poisonous effect of O2 was turned off.

The environmental impact of the GOE was global in the true sense of the word. The accumulation of oxygen in the atmosphere had three major consequences:

Mitochondria arose after the GOE, the Cambrian explosion took place at the transition between level 4 and 5 (see line graph above) instead.

Evidence of free oxygen before the GOE

There are indications that even before the GOE considerable amounts of unbound oxygen in the atmosphere must have been. So show about 3 billion years old paleosols and evaporites in South Africa were strong indications for oxygen weathering. This could be an indication of emerging at this time photosynthetic cyanobacteria.