Where does oxygen on Earth come from?

Where does oxygen on Earth come from?

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2021-08-07 08:24:07

In the first half of the history of The earth there’s no oxygen at all, but that doesn’t mean life doesn’t exist. At present, there is still much controversy about the main biological factors in the world.”pre-oxygen“, researchers are looking for evidence from within the oldest sedimentary rocks on our planet.

Most scientists assume that the amount of oxygen in the atmosphere was negligible until 2.4 billion years ago, when the GOE occurred. At that moment, the oxygen level seemed to suddenly spike. This jump in oxygen concentration is mainly due to cyanobacteria (cyanobacteria), also called green algae – photosynthetic bacteria that release oxygen.

GOE explanation: The Great Oxidation Event – ​​also known as the Oxygen Catastrophe, is the biologically-induced appearance of O2 in the earth’s atmosphere.

How and when this oxygen-emitting bacterium appeared and when it appeared is still not clear, because the fact that the GOE event occurred at the intersection of three factors at the same time: global freezing, mineral fluctuations and the abundance of new species.

We don’t know what the cause is and what the effect is. Many events happened at the same time, so its story is still unclear” – doctor Dominic Papineau at the Carnegie Washington Institute said.

To help classify geological maps, Papineau study the formation of banded iron layers (banded iron formations – BIFs), sedimentary rocks that formed at the bottom of ancient seas.

Papineau’s research, supported by NASA’s Evolutionary Biology Program, focusing on specific minerals in BIFs may be closely related to life (and death) of ancient microorganisms.

Exploiting the formation of iron strata to form BIFs

Exploiting the formation of iron strata to form BIFs

Iron minerals in BIFs are the largest source of iron ore in the world. However, this stone is worth more than making steel. Geologists have mined them by documenting their rich history spanning 3.8 billion to 0.8 billion years ago.

However, the origin of the oldest BIFs remains a mystery. What scientists need is the help of organisms to form the current common sense, but which species? Single-celled marine organisms don’t leave behind any bones or shells for us to understand, but Papineau thinks there may be minerals or geochemical fossils in the BIFs.

He and his colleagues found that the carbon material in BIFs is closely related to apatite – a mineral containing phosphorus. This means that what forms in BIFs lies in their finished products.

To verify this, Papineau’s team will study the carbon contained in the BIF and compare it with other carbon minerals that are not of biological origin, including those found in a Martian meteorite .

This study has the potential to demonstrate that bacterial biomass is bound and deposited together with iron minerals” – professor Andreas Kappler from the University of Tuebingen in Germany, who was not involved in the study.

Early appearance of “oxygen released”

The early arrival of "exhaled oxygen"

It is possible that the bacteria built into the BIF are cyanobacteria, because the oxygen from these bacteria causes the iron to oxidize in the seas before GOE event. But if cyanobacteria appeared before the GOE, why did it take hundreds of millions of years for the oxygen released to accumulate in the atmosphere?

Papineau and his colleagues found part of the answer in the complex intersection of biology and geography. Oxygen from cyanobacteria can be destroyed by the predominance of methane. These two gases react with each other to produce carbon dioxide (CO2) and water.

Oxygen cannot accumulate in an environment rich in methane” said Papineau.

Methane is thought to come from bacteria called methane-producing bacteria (methanogens), releasing methane after consuming carbon dioxide and hydrogen gas.

In this case, the methanogens and cyanobacteria shared the ancient sea, but the methanogens dominated—releasing methane, constraining oxygen, and warming the planet with the greenhouse effect. However, by the time of the GOE event, these organisms were beginning to fade away and the depletion of atmospheric methane filled with oxygen from cyanobacteria.

No “nickel” to reserve

Electron microscopy image of methanogenic bacteria.Electron microscopy image of methanogenic bacteria.

Connecting the GOE event to the reduction of methanogens has been mentioned before, but there is still little evidence to support the disappearance of nickel. Recently, however, Dr. Papineau and his colleagues announced in the journal Nature that: “About 2.7 billion years ago, the nickel concentration in BIFs dropped dramatically“.

Content nickel in the ocean fell by 50% just before the GOE event. This is important because methanogens depend on nickel to live: it is the main raw material for enzymes involved in metabolism in the process of methane formation. When the nickel content decreases, it means that the methanogens will be “starve“.

The case of nickel scarcity makes the pre-GOE development of cyanobacteria more plausible, but more evidence is still needed to support this.

Kappler believes: “Research on the origin of oldest BIFs can tell us life evolved the ability to exhale oxygen and thus change the world forever“.

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