Geological history of oxygen

Source: Wikipedia, the free encyclopedia.
Ga).
Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere.
Stage 2 (2.45–1.85 Ga): O2 produced, but absorbed in oceans and seabed rock.
Stage 3 (1.85–0.85 Ga): O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer.
Stages 4 and 5 (0.85 Ga–present): O2 sinks filled, the gas accumulates.[1]

Before photosynthesis evolved, Earth's atmosphere had no free oxygen (O2).[2] Small quantities of oxygen were released by geological[3] and biological processes, but did not build up in the atmosphere due to reactions with reducing minerals.

Oxygen began building up in the atmosphere at approximately 1.85 Ga. At current rates of primary production, today's concentration of oxygen could be produced by photosynthetic organisms in 2,000 years.[4] In the absence of plants, the rate of oxygen production by photosynthesis was slower in the Precambrian, and the concentrations of O2 attained were less than 10% of today's and probably fluctuated greatly.

The increase in oxygen concentrations had wide ranging and significant impacts on life. Most significantly, the rise of oxygen caused a mass extinction of anaerobic microbes and paved the way for multicellular life.

Before the Great Oxidation Event

Great Oxygenation Event.[6]

Effects on life

Early fluctuations in oxygen concentration had little direct effect on life, with

arthropods, including insects, millipedes and scorpions.[9] Whilst human activities, such as the burning of fossil fuels, affect relative carbon dioxide concentrations, their effect on the much larger concentration of oxygen is less significant.[12]

The Great Oxygenation Event had the first major effect on the course of evolution. Due to the rapid buildup of oxygen in the atmosphere, many organisms not reliant on oxygen to live died.[9] The concentration of oxygen in the atmosphere is often cited as a possible contributor to large-scale evolutionary phenomena, such as the Avalon explosion, the Cambrian explosion, trends in animal body size,[13] and other diversification and extinction events.[9]

Data show an increase in biovolume soon after the Great Oxygenation Event by more than 100-fold and a moderate correlation between atmospheric oxygen and maximum body size later in the geological record.

Carboniferous period, when the oxygen concentration in the atmosphere reached 35%, has been attributed to the limiting role of diffusion in these organisms' metabolism.[14] But Haldane's essay[15] points out that it would only apply to insects. However, the biological basis for this correlation is not firm, and many lines of evidence show that oxygen concentration is not size-limiting in modern insects.[9] Ecological constraints can better explain the diminutive size of post-Carboniferous dragonflies – for instance, the appearance of flying competitors such as pterosaurs, birds and bats.[9]

Rising oxygen concentrations have been cited as one of several drivers for evolutionary diversification, although the physiological arguments behind such arguments are questionable, and a consistent pattern between oxygen concentrations and the rate of evolution is not clearly evident.

metazoa first appeared in the fossil record.[9] Further, anoxic or otherwise chemically "inhospitable" oceanic conditions that resemble those supposed to inhibit macroscopic life re-occur at intervals through the early Cambrian, and also in the late Cretaceous – with no apparent effect on lifeforms at these times.[9] This might suggest that the geochemical signatures found in ocean sediments reflect the atmosphere in a different way before the Cambrian – perhaps as a result of the fundamentally different mode of nutrient cycling in the absence of planktivory.[7][9]

An oxygen-rich atmosphere can release phosphorus and iron from rock, by weathering, and these elements then become available for sustenance of new species whose metabolisms require these elements as oxides.[2]

References

  1. ^
    PMID 16754606
    .
  2. ^
    New York Times
    . Retrieved 3 October 2013.
  3. PMID 35941147
    .
  4. PMID 5859927
    .
  5. doi:10.1130/G22360.1
    .
  6. S2CID 25260892
    .
  7. ^
    S2CID 59436643
    .
  8. ISBN 978-0-13-140941-5
    .
  9. ^
    S2CID 31074331
    .
  10. PMID 10500106
    .
  11. ^ Earliest record of wildfires provides insights into Earth's past vegetation and oxygen levels
  12. ISBN 978-0-19-850340-8
    .
  13. ^ a b Payne, J. L.; McClain, C. R.; Boyer, A. G; Brown, J. H.; Finnegan, S.; et al. (2011). "The evolutionary consequences of oxygenic photosynthesis: a body size perspective". Photosynth. Res. 1007: 37-57. DOI 10.1007/s11120-010-9593-1
  14. doi:10.29173/eureka10299
    .
  15. ^ Haldane, J.B.S., On being the right size, paragraph 7
  16. S2CID 4405370
    .

External links
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