The origin of oxygen on Earth

The first half of Earth's history is completely free of oxygen, but that doesn't mean there's no life. There is still a lot of controversy with the main biological elements in the 'oxygen money' world and researchers are looking for clues from the oldest sedimentary rocks on our planet.

Most scientists believe that the amount of oxygen in the atmosphere is negligible until 2.4 billion years ago, when the Great Oxidation Event (GOE) occurred. The jump in oxygen concentration is mainly caused by cyanobacteria - photosynthetic bacteria that breathe oxygen. When and how this oxygen-producing bacterium appears is unknown, due to the fact that the GOE event is the intersection of global freezing, mineral volatility and the abundance of new species.

The cyanobacteria scum is now considered a nuisance, but these bacteria have oxidized our planet 2 billion years ago. (Photo: Department of Health, Washington State)

Dominic Papineau of the Carnegie Institution of Washington, said: 'We don't know what the cause is and what the consequences are. Some events happen at the same time, so the story is still unclear. ' To help solve this geographic question, Papineau is studying banded iron formations (BIFs) or iron formation, sedimentary rocks formed at the bottom of ancient seas.

Papineau's research, funded by NASA's Evolutionary Biology Program, focuses on certain minerals within BIFs that may be closely related to the life (and death) of ancient bacteria.

Learn BIFs

Iron minerals in BIFs are the largest source of iron ore in the world. However, these stones are much more valuable than steel.Geographers exploit them because of rich historical records that last from 3.8 billion to 0.8 billion years ago.

However, the oldest source of BIF is still a mystery. Scientists think that they need the help of organisms to be able to form, but which organisms? The unicellular marine animals do not leave bones or shells so we can find out, but Papineau thinks that there may still be minerals or fossilized localization in BIFs.

Banded iron formation (BIF). (Photo: Paul Hoffman, Harvard University) He and colleagues discovered carbon materials in BIFs related to apatite, a phosphate mineral that is often closely related to biology. This means that what constitutes BIF is still in their own products.

To test this, Papineau's team will study the carbon in BIF and compare it with other non-biological carbon-based minerals, including minerals found in a Martian meteorite.

Andreas Kappler of Tuebingen University in Germany, who is not involved in the study, said: 'This research has the potential to prove that bacterial biomass is linked and deposited with iron minerals'.

The early occurrence of bacteria exhaling oxygen

It is possible that the bacteria that make up BIF are cyanobacteria, because the oxygen from these bacteria causes iron to oxidize in the seas before the GOE event.

But if the cyanobacteria appeared long before the GOE, why does it take hundreds of millions of years for the oxygen they breathe to accumulate in the atmosphere?

Papineau and colleagues may have found part of the answer in the complex context of biology and geography.

Oxygen from cyanobacteria may have been destroyed due to the superiority of methane. These two gases react with each other to produce carbon dioxide and water.

Papineau explains: 'Oxygen cannot accumulate in methane-rich environments'.

Methane is thought to originate from bacteria called methanogens, which release methane after consuming carbon dioxide and hydrogen.

In this case, methanogen and cyanobacteria share ancient waters, but methanogens dominate - their methane release inhibits oxygen, and warms the planet through a greenhouse effect. However, until the time of GOE, these organisms began to disappear, and oxygen from the cyanobacteria filled the atmosphere was exhausted of methane.

Poor

Linking the GOE event with the decline of methanogen has been mentioned before, but there is little evidence to support this hypothesis. However, recently Papineau and colleagues reported in Nature that the concentration of nickel in BIFs dropped significantly by 2.7 billion years ago.

Sea level of nickel is reduced by 50% just before GOE happens. This is important because methanogens depend on nickel: it is the central material for metabolic enzymes involved in methane formation.When nickel levels decrease, methanogens are 'hungry'.

The situation of scarce nickel makes the pre-GOE development of cyanobacteria more reasonable, but more evidence is needed to confirm this.

Kappler believes that studying the origin of the oldest BIFs can tell us when life begins to develop the ability to breathe oxygen and thus change the world forever.