Geological history of oxygen

src: rstb.royalsocietypublishing.org

Before photosynthesis evolved, Earth's atmosphere lacked free oxygen (O ₂ ). The photosynthetic prokaryotic organism that produces O ₂ as a living waste product long before the first buildup of free oxygen in the atmosphere, probably since 3.5 billion years ago. The oxygen they produce will be quickly removed from the atmosphere by weathering from minerals, especially iron. This "rusty mass" causes deposition of iron oxide in the seafloor, forming banded iron formations. Oxygen only began to survive in the atmosphere in small amounts about 50 million years before the start of the Great Oxygenation Event. This atmospheric mass oxygenation results in a rapid buildup of free oxygen. At the current primary production level, the current oxygen concentration can be produced by photosynthetic organisms within 2,000 years. In the absence of plants, the rate of oxygen production by photosynthesis is slower in Precambrian, and the concentration of O ₂ is achieved less than 10% from today and may be highly fluctuating; oxygen may even have disappeared from the atmosphere about 1.9 billion years ago. This oxygen concentration fluctuation has little direct effect on life, with mass extinctions not observed until the emergence of complex life around the beginning of the Cambrian period, 541 million years ago . The presence of O
₂ with new opportunities. Aerobic metabolism is more efficient than anaerobic pathways, and the presence of oxygen undoubtedly creates new possibilities for life to explore. Since the beginning of the Cambrian period, atmospheric oxygen concentrations have fluctuated between 15% and 35% of atmospheric volume. A maximum of 35% was reached towards the end of the Carbon period (about 300 million years ago), a peak that may have contributed to the large size of insects and amphibians at that time. While human activity, such as the burning of fossil fuels, affects the relative concentrations of carbon dioxide, its effects on much larger oxygen concentrations are less significant.

Video Geological history of oxygen

Effects on life

The concentration of oxygen in the atmosphere is often cited as a possible contributor to large-scale evolutionary phenomena, such as the origins of multicellular Edyacara biota, Cambrian explosions, animal body size trends, and other extinctions and diversification events.

The large size of insects and amphibians in the Carboniferous period, when the concentration of oxygen in the atmosphere reached 35%, has been linked to the role of limiting the diffusion in the metabolism of these organisms. But Haldane's essay shows that it applies only to insects. However, the biological basis for this correlation is not clear, and many lines of evidence suggest that oxygen concentrations do not limit the size of modern insects. There is no significant correlation between atmospheric oxygen and maximum body size elsewhere in the geological record. Ecological constraints can better explain the small size of post-carbon dragonflies - for example, the emergence of flying competitors such as pterosaurs, birds and bats.

Increased oxygen concentrations have been referred to as one of several movers for evolutionary diversification, although the physiological argument behind the argument is questionable, and the consistent pattern between oxygen concentration and evolution rate is unclear. The most famous relationship between oxygen and evolution occurs at the end of the last glacial snowball, in which complex multicellular life was first discovered in the fossil record. Under low oxygen concentrations and before the evolution of nitrogen fixation, biologically available nitrogen compounds are in limited supply and periodic "nitrogen crises" can make the sea unfriendly to life. A significant oxygen concentration is just one of the prerequisites for the evolution of complex life. The model based on the uniformitarian principle (ie extrapolating the current marine dynamics into the depth of time) shows that such concentration is achieved only immediately before metazoa first appears in the fossil record. Furthermore, the conditions of anoxic or chemical-like "odorous" oceans that should inhibit macroscopic life again occur at intervals through the beginning of the Cambrian, and also at the end of the Cretaceous - with no real effect on life forms at times this. This may indicate that the geochemical signs found in marine sediments reflect the atmosphere in different ways before the Cambrian - perhaps as a result of a very different nutrient cycle mode in the absence of planktivory.

Oxygen in the atmosphere can cause phosphorus and iron to be released from rocks, and these elements can then be used to build new species that need these elements.

Maps Geological history of oxygen

References

src: www.pnas.org

External links

• First breath: Earth's billion-year battle for oxygen (subscription required) New Scientist, # 2746, February 5, 2010 by Nick Lane.
• The Earth Oxygen Mystery of the New York Times, October 3, 2013 by Carl Zimmer.
• From the Thin Air, Dinosaurs, Birds and the Earth's Ancient Earth Joseph Henry Press, ISBNÃ, 0-309-10061-5 2006 by Peter D. Ward.

Source of the article : Wikipedia