Changes in oxygen levels and consequences

On Earth, only arches (archaeobacteria) and anaerobic bacteria are able to live without oxygen.

Origin of oxygen

Oxygen comes from the activity of cyanobacteria, plants using chlorophyll which extracts carbon on carbon dioxide and reject oxygen; This is the mechanism of photosynthesis.

Water vapor is also transformed into dioxygen and dihydrogen, once in the upper atmosphere due to the evaporation caused by the sun’s rays.

Four billion years ago, the Earth’s atmosphere was composed mainly of methane, ammonia and carbon dioxide. The bacteria in the oceans then practiced fermentation. Until the appearance of mutant bacteria that have used photosynthesis by consuming carbon from CO2. These bacteria have continued to mutate to become cyanobacteria, they appeared 3.2 billion years ago in the form of blue-green algae or blue-green algae. They were then especially interested in the hydrogen of water.

Change in the amount of oxygen in the atmosphere

2.7 billion years ago, the concentration of oxygen reached 2% of the composition of the earth’s atmosphere. Anaerobic bacteria have begun to disappear.

540 million years ago, during the Cambrian, the oxygen level reached 15% and fluctuated between this level and 30%.

300 million years ago, during the Permian period, oxygen reached a maximum of 35%. The insects then metamorphosed, taking gigantic sizes, just like the amphibians.

So on Earth, the dragonflies had a 24 inches wingspan, the scorpions were 30 inches long, the spiders were as big as a human head and devoured the small reptiles, centipedes were 6.5 feet long.

This is due to the growth of the giant fern forests (the size of a tree) on the planet, as well as the buried organic matter, turning into coal deposits.

The amount of oxygen being too great, the storms began to ignite the sky, which gradually decreased the rate. Reptiles have succeeded insects. The oxygen content then fell to 10-15%, temperatures rose, as did the CO2 concentrations.

Human activities do not change the amount of oxygen in the atmosphere, despite the burning of nearly 7 billion tons of fossil fuels.

If oxygen disappeared overnight, it would take only 2,000 years for nature to produce the same oxygen content, photosynthesis now having a frantic rhythm.

In order for us to reach about 30-35% oxygen again on Earth, the continents would have to merge again, to create a new Pangea, and this one would travel to the tropical zones of the earth. The moisture content will then allow the renewal of the fern. It would have to mutate to reach peaks and produce considerable amounts of oxygen.

At present, it is the algae and the marine phytoplankton that produce the most oxygen on Earth, and then the forests.

Why does not the current rate increase?

If nature can recreate the rate of the 21st century in less than 2000 years by starting from scratch, why does the current rate not go beyond 20-21%?

O2 is mainly produced by photosynthesis. Water and CO2 are recovered by plants to create carbohydrates (CH2O), then O2 is also released.

But in the evening, the plant breathes O2 to release CO2, so the forests often have a record of almost zero over several years. Thus the Amazon is not the real lung of the planet (it is above all the largest pool of the diversification of the living), it is rather the oceans that should have this title.

The oceans via algae and phytoplankton release a lot of oxygen, part is breathed by the terrestrial alive beings, the other goes into the atmosphere. But oxygen is also used in iron oxidation outside. Also, a large part of the organic matter in the water will oxidize, while the other is deposited at the bottom of the oceans.

In order for the oxygen level to increase, the photosynthetic activity must increase, the organic matter (carbon) must be buried rather than oxidized, so that oxygen remains free and take off. This is what happened during the Carboniferous-Permian.


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