When did oxygen appear on the globe?

Mohammed Shaban

In the first known chapter of the antiquity, the actors of this story began to play their roles. Her hero, later known as oxygen, missed this chapter.

This absence lasted long, starting from more than four billion years to 2.5 billion years, making viewers of that era of primitive monocellular organisms that rely on food sulfur as a source of energy.

Between sulfur and oxygen
This separation changed when bluish green bacteria attempted photosynthesis, producing oxygen in the atmosphere for about 2.5 to 2.3 billion years.

But the story of the "rise of oxygen" into the atmosphere - one of the greatest stories of Earth's history - is always told by the rival hero, sulfur.

This is due to the availability of stable sulfur isotopes in rocky sediments of the seas and oceans.

With the advent of oxygen, the proportion of isotopes of sulfur began to change. Hence, scientists infer the timing of the emergence of oxygen in this scene, by analyzing the sedimentary rocks and the date range in which the observed isotope sulfur change in these rocks.

Stable isotopes of sulfur
In a recent EU-funded study published in the journal Nature Communications on October 29, scientists at the European Institute of Oceanography in France presented a new perspective on understanding the story of oxygen on Earth.

The stable isotopes of sulfur preserved in sedimentary rocks on the seabed and oceans are important clues to the timing of oxygen on Earth.

These sulfur isotopes show a distinct response to change in oxygen at levels below one in 1,000 percent of what is now in the atmosphere.

The lack of oxygen gas 2.5 billion years ago has given some chemical reactions to the atmosphere using sulfur gases, which lead to stable sulfur isotopes in rocks older than 2.5 billion years. But these isotopes disappeared from the rocks between 2.5 and 2.3 billion years ago.

Thus, according to Kellinsworth, this time period was considered to be the period in which enough oxygen accumulated in the atmosphere, preventing sulfur-based chemical reactions from occurring.

However, we do not have an explanation of how sulfur isotopes change when they first interact with oxygen, nor do we know the local factors that may have affected sulfur isotopes formed in the past.

The absence of sulfur is not evidence
By analyzing some of Australia's 2.31 billion-year-old rocks, scientists found one of its stable isotopes of sulfur. Scientists have been able to show that some stable isotopes of sulfur - an indicator of low oxygen - can turn into rocks that indicate an increase in oxygen, which means that the atmospheric factors that occurred to the rocks in the past may be the reason for our mistaken conclusion about the lack of oxygen in the atmosphere Aerial, even if the opposite.

Therefore, the inferiority of oxygen due to the presence of these sulfur-containing isotopes is wrong.

"The main problem of determining the timing of oxygen in the atmosphere and linking it to the disappearance of sulfur isotopes from these rocks about 2.3 billion years ago is that we hypothesized that there is no sulfate recycling in the rocks. More recently, it made us believe that oxygen had come into the atmosphere at a newer time (2.3 billion years) than it actually was. ”

Future hopes
The researchers found a stable isotope of sulfur and oxygen together - called barite - in the discovered rocks dating back to 2.31 billion years. Barites were found in rocks formed near the shore along with other fossils and sedimentary stromatolites.

"This study enabled us to find out whether the isotopes of sulfur in the rocks, which existed 2.3 billion years ago, reflect the state of the atmosphere at the time, or is it just a recycling that happened to sulfur and then reappeared in This time talking.

This is critical, as we used to associate the emergence of isotopes of sulfur in sedimentary rocks with a lack of oxygen in the atmosphere. So the presence of sulfur at this relatively recent time (2.3 to 2.5 billion years) does not mean that oxygen was not available during that period.

"In our research, we have refuted this concept, which may help future studies determine the timing of oxygen in our atmosphere more precisely," Kellensworth said.