Great oxygen disaster

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Temporal classification of the Great Oxygen Disaster (GOE) in evolutionary history

The great oxygenation event (GOE after english great oxygenation event ) was the increase in the concentration of molecular oxygen (O 2 ) in shallow waters and the atmosphere several orders of magnitude in a relatively short time before about 2.4 billion years ago, at the Archean-Proterozoic -Boundary when the earth was half its age. In the evolution of the earth's atmosphere , the great oxygen catastrophe represents the transition from the second to the third atmosphere.

Some of the then all anaerobic organisms produced oxygen as a toxic waste product of photosynthesis , probably for hundreds of millions of years. But initially easily oxidizable substances of volcanic origin (hydrogen, carbon, sulfur, iron) kept the O 2 concentration very low, below 0.001% of today's level (10 −5 PAL, English present atmospheric level ), as the characteristic proportions of sulfur isotopes prove. During this time the color of the earth changed from basalt black to rust red. Decreasing volcanism, the loss of hydrogen into space and an increase in photosynthesis then led to GOE, which today is understood as a period with multiple increases and decreases in O 2 concentration.

The GOE was immediately followed by an icing of the planet, because the greenhouse gas methane was broken down more quickly in the oxidizing atmosphere, and deposits of large amounts of organic material, see Lomagundi-Jatuli isotope excursion . The δ 13 C values ​​indicate an amount of released oxygen corresponding to 10 to 20 times the current O 2 inventory in the atmosphere. The O 2 concentration then fell to moderate levels for a long time, probably mostly below 10 −3 PAL, only to rise again less than 1 billion years ago, which finally made multicellular life possible.

procedure

Outdated concept of monotonous O 2 enrichment.
Above: atmosphere, middle: shallow oceans, below: deep oceans,
abscissa: time in billions of years (Ga). Ordinates: O 2 partial pressure of the atmosphere in atm or molar O 2 concentration in sea water in µmol / L. The two curves in each graph denote the upper and lower limits of the estimation range (Holland, 2006).
Ribbon ore. This block of iron ore from North America , weighing around 8.5 tons, three meters wide and 2.1 billion years old, belongs to the Museum of Mineralogy and Geology Dresden and is located in the Dresden Botanical Garden .

The primordial atmosphere of the earth contained free oxygen (O 2 ) at best in very low concentrations. Years ago, probably about 3.2 to 2.8 billion developed microorganisms , according to current knowledge forerunner of today's cyanobacteria , from a simple photosynthesis form a new, as opposed to the older form O at the 2 produced as a waste product and therefore as oxygenic photosynthesis is called . As a result, significant amounts of O 2 were formed in the oceans both before and after the Great Oxygen Disaster. There was, however, one essential difference: Before the Great Oxygen Catastrophe, the oxygen formed was completely bound in the oxidation of organic substances, hydrogen sulfide and dissolved iron (present as a divalent iron ion Fe 2+ ). The GOE was the point in time at which these substances, especially Fe 2+ , were largely oxidized and the new entry of these substances could no longer completely bind the oxygen formed. The excess free oxygen began to accumulate in the sea water and in the atmosphere.

It is generally assumed that a long time passed between the occurrence of oxygenic photosynthesis with the associated production of O 2 and the start of the enrichment of free oxygen, because large amounts of substances oxidizable with O 2 were present and supplied from weathering and volcanism so the O 2 formed was immediately bound.

The oxidation of Fe 2+ to trivalent iron ions Fe 3+ resulted in the deposition of banded iron formation ( banded iron formation ), where iron mainly in the form of oxides , namely, hematite Fe 2 O 3 and magnetite Fe 3 O 4 is present. In old continent shields, which have been relatively little tectonically changed over a long period of time, such ribbon ores have been preserved to this day, e.g. Hamersley Basin (Western Australia), Transvaal Craton (South Africa), Animikie Group ( Minnesota , USA). They are the most important iron ores globally . Oxygen only began to remain in the atmosphere shortly (around 50 million years) before the GOE.

Theory of the late appearance of oxygenic photosynthesis

According to this theory, the phototrophic oxygen producers did not develop until immediately before the greater increase in atmospheric oxygen concentration. The theory is based on the mass-independent fractionation of sulfur isotopes, which is assigned an indicator function for oxygen. With this theory, the time span between the evolution of oxygen photosynthetic microorganisms and the point in time when the O 2 concentration rises needs no explanation.

However, there is a possibility that the oxygen indicator has been misinterpreted. In the course of the proposed time lag of the above-mentioned theory, a change from mass-independent fractionation (MIF) to mass-dependent fractionation (MDF) of sulfur took place. It is believed that this was the result of the appearance of oxygen O 2 in the atmosphere. Oxygen would have prevented the photolysis of sulfur dioxide causing MIF . This switch from MIF to MDF of the sulfur isotopes could also have been caused by an increase in glacial weathering. A homogenization of the marine sulfur deposits as a result of an increased temperature gradient during the Huronian glaciation is also possible .

Trail theory

The lag (which could have been up to 900 million years) is the time lag between the point in time at which the oxygen production of photosynthetically active organisms started and the rapid rise in atmospheric oxygen (in geological periods) about 2.5 to 2 years ago , 4 billion years ago. A number of hypotheses are used to try to explain this time lag.

Tectonic trigger

According to this theory, the time lag is explained by the fact that the increase in oxygen had to wait for tectonically induced changes in the “anatomy” of the earth. It was the appearance of shelf seas where reduced carbon could reach the sediments and be deposited there. In addition, the newly produced oxygen was initially bound in various oxidations in the ocean, primarily in an oxidation of divalent iron. There is evidence of this phenomenon in older rock formations, namely large quantities of ribbon ores apparently deposited by iron oxidation. Ribbon ores make up the bulk of commercially mineable iron ores .

Nickel deficiency

Chemosynthetic organisms were a source of methane. But methane was a trap for molecular oxygen, because oxygen oxidizes methane in the presence of UV radiation to carbon dioxide and water without any further action . Today's methane-producing microbes need nickel as a coenzyme . As the earth's crust cooled, the supply of nickel and thus methane production was reduced, allowing oxygen to dominate the atmosphere. In the period from 2.7 to 2.4 billion years ago, the amount of nickel deposited steadily decreased; it was originally 400 times the current level.

Consequences of the Great Oxygen Disaster

Rising oxygen levels in the oceans may have wiped out a large part of the obligate anaerobic organisms that populated the earth at the time. The oxygen was deadly for obligate anaerobic organisms and essentially responsible for what is probably the greatest mass extinction . In organisms that are not adapted to O 2 , peroxides form in the course of their metabolism , which are very reactive and damage vital components of the organisms. Presumably, living beings developed enzymes ( peroxidases ) during the time when O 2 was formed but always consumed in oxidations , which destroy the peroxides that were formed, so that the poisonous effect of the O 2 was switched off.

The environmental impact of the Great Oxygen Disaster was global. The enrichment of oxygen in the atmosphere had three other serious consequences:

  1. Atmospheric methane (a powerful greenhouse gas ) was oxidized to carbon dioxide (a weaker greenhouse gas) and water, which started the Huron Ice Age . The latter could have been a complete and, if at all, the longest Snowball Earth episode in Earth's history, lasting from approximately −2.4 to −2.0 billion years.
  2. Free oxygen led to enormous changes in the chemical interaction between the earth's solids on the one hand and the earth's atmosphere, the oceans and other surface waters on the other. The variety of minerals found on earth increased greatly. It is estimated that the GOE alone is responsible for more than 2500 of the 4500 or so minerals. The majority of these minerals were aqua complexes or oxidized forms of the minerals that formed due to dynamic earth mantle and earth crust processes according to the GOE.
  3. The increased oxygen content opened new ways for the evolution of living things. Despite the natural recycling of organic substances, anaerobic organisms are energetically limited. The availability of free oxygen in the atmosphere was a breakthrough in the evolution of energy metabolism; it greatly increased the supply of thermodynamically free energy to living beings. Because with a large number of substances, the oxidation with O 2 releases considerably more usable energy than a metabolism without oxidation with O 2 .

Mitochondria emerged after the Great Oxygen Disaster, the Cambrian explosion took place at the transition between stages 4 and 5 (see line diagram above).

Evidence of free oxygen prior to the Great Oxygen Disaster

There are indications that there must have been episodes with O 2 partial pressures of at least one 3000th of the current level before the GOE . For example, about 3 billion year old paleo soils and evaporites in South Africa show strong signs of oxygen weathering. This could be an indication of photosynthesizing protocyanobacteria that were developing at this time.

literature

  • Timothy W. Lyons, Christopher T. Reinhard, Noah J. Planavsky: The rise of oxygen in Earth's early ocean and atmosphere. Nature 506, 2014, doi: 10.1038 / nature13068 ( online ).

Individual evidence

  1. ↑ https://www.mpg.de/forschung/eukaryoten-evolution
  2. ↑ Heinrich D. Holland: The oxygenation of the atmosphere and oceans (PDF; 781 kB). In: Phil. Trans. R. Soc. B , Volume 361, 2006, pp. 903-915.
  3. ↑ Ariel D. Anbar, Yun Duan, Timothy W. Lyons, Gail L. Arnold, Brian Kendall, Robert A. Creaser, Alan J. Kaufman, Gwyneth W. Gordon, Clinton Scott, Jessica Garvin, and Roger Buick: A whiff of oxygen before the great oxidation event? In: Science. Volume 317, No. 5846, September 28, 2007, pp. 1903-1906, doi: 10.1126 / science.1140325 .
  4. ^ A b c Robert E. Kopp, Joseph L. Kirschvink, Isaac A. Hilburn, and Cody Z. Nash: The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis . In: Proc. Natl. Acad. Sci. USA Vol. 102, No. 32 , 2005, pp. 11131–11136 , doi : 10.1073 / pnas.0504878102 , PMID 16061801 , PMC 1183582 (free full text), bibcode : 2005PNAS..10211131K (English, pnas.org ).
  5. ↑ TM Lenton, HJ Schellnhuber, E. Szathmáry: Climbing the co-evolution ladder . In: Nature . Vol. 431, No. 7011 , 2004, p. 913 , doi : 10.1038 / 431913a , PMID 15496901 , bibcode : 2004Natur.431..913L (English).
  6. ↑ Kurt O. Konhauser et al .: Oceanic nickel depletion and a methanogen famine before the great oxidation event . In: Nature . Vol. 458, No. 7239 , 2009, p. 750–753 , doi : 10.1038 / nature07858 , PMID 19360085 , bibcode : 2009Natur.458..750K (English).
  7. ^ Adriana Dutkiewicz, Herbert Volk, Simon C. George, John Ridley, Roger Buick: Biomarkers from Huronian oil-bearing fluid inclusions: An uncontaminated record of life before the Great Oxidation Event . In: Geology . tape 34 , no. 6 , January 6, 2006, p. 437-440 , doi : 10.1130 / G22360.1 (English).
  8. ^ First breath: Earth's billion-year struggle for oxygen. In: New Scientist , Volume 2746, February 5, 2010, Nick Lane: A snowball period, c2.4 - c2.0 Gya, triggered by the oxygen catastrophe ( Memento of January 6, 2011 in the Internet Archive ) .
  9. ^ Robert M. Hazen: Evolution of Minerals . In: Scientific American 302, 2010, doi: 10.1038 / scientificamerican0310-58 ( full text online ).
  10. ↑ Sean A. Crowe, Lasse N. Døssing, […] Donald E. Canfield: Atmospheric oxygenation three billion years ago . In: Nature . tape 501 , September 26, 2013, p. 535-538 , doi : 10.1038 / nature12426 (English, nature.com ).