To date, 21% of the air we breathe consists of molecular oxygen. But this gas was not always in such quantity, are not always able to support life — indeed, virtually absent in the atmosphere during the first 2 billion years of Earth’s history. When oxygen first began to gather on Earth? Scientists at mit have found the answer. In a paper published recently in Science Advances, a group of scientists announced that the Earth’s atmosphere has experienced the first tangible and irreversible injection of oxygen approximately 2,33 billion years ago. This period marked the beginning of the great oxygenation event, after which oxygen began his victorious attack on the Ground.
Scientists have also determined that this initial rise of atmospheric oxygen, though small, occurred in only 1-10 million years and caused a series of events that led to the proliferation of multicellular life.
“This is the beginning of a very long period, which resulted in a complicated life,” says Roger Sammons, senior author and Professor in the Department of earth, atmospheric and planetary Sciences at MIT. — It took about 1.7 billion years to have evolved animals, such as those that we have today. But the presence of molecular oxygen in the ocean and atmosphere means that the organisms that breathe oxygen could thrive”.
The air smelled of oxygen
In General, scientists agree that oxygen, despite the lack of in the atmosphere most likely was brewed in the ocean as a by-product of photosynthesis cyanobacteria already 3 billion years ago. But according to Sammons, the oxygen in the ancient ocean “instantly absorbed” with hungry microbes, ferrous iron and other interested persons, not letting him escape into the atmosphere.
“In the air could be leaking oxygen before, but their duration and content are currently impossible to measure,” says Sammons.
Everything changed with the period of the great oxygenation, which marked the beginning of the permanent presence of oxygen in the atmosphere. Previous estimates had put the start IN at around 2.3 billion years with uncertainty of tens or hundreds of millions of years.
“The Dating of this event has remained fairly inaccurate still,” says Sammons.
Forced to move
To accurately determine the time of occurrence IN the Sammons colleagues first analyzed the rocks of that period in search of a specific pattern of isotope of sulfur. When volcanoes erupt, they emit sulfur gases that can chemically and isotopically separated under the influence of ultraviolet radiation. The structure of the isotopes formed in this process depends on the fact that there was oxygen above a certain threshold or not.
Scientists have tried to identify major transition in a specific isotope pattern series — mass-independent fraction of sulfur isotopes (S-MIF) in order to determine when oxygen first appeared in Earth’s atmosphere. For this they studied from sediment cores collected during the expedition, scientists in South Africa.
“Jingmin Luo is a very hardworking guy,” says Sammons about another scientist who participated in the writing of this work. — He found traces of S-MIF in the deep rocks, the absence of these traces in the shallow rocks, but between them, nothing. So he returned back to South Africa”.
There he took samples from the rest of the sediment cores and the two nearby and found that the transition S-MIF meaning permanent bridging oxygen of the above — mentioned threshold of 2.33 happened a billion years ago, plus or minus 7 million years. The uncertainty is much lower when compared with previous estimates.
The scientists also found a large isotope fractionation of sulphur-34, which indicates the increase of sea level of sulfates at the same time. This sulfate was supposed to appear due to the reaction between atmospheric oxygen and sulfide minerals on land, as well as sulfur dioxide from volcanoes. Then this sulfate was used by the inhabitants of the ocean, sulfate-breathing bacteria, with the production of a specific pattern of sulfur-34 in lower layers of sedimentary rocks that have been dated between 1 and 10 million years after the transition of S-MIF.
These results indicate that the initial accumulation of oxygen in the atmosphere was relatively quick. Since its first appearance 2,33 billion years ago, oxygen accumulated in sufficiently high concentrations to exert vyvetrivaniya effect on the breed in 10 million years. This process of weathering has vasilciuc more of sulphate and some metals in the water and thus into the oceans. Sammons indicates that it took some time, before the earth system reached a stable state by the burial of organic carbon and exceeded the threshold of oxygen required for further stimulation of biological evolution.
“Complex life could not be approved on the planet, while the oxygen remained the prerogative of the ocean depths,” says Sammons. And it took a long, long time. But this is the first step in a series of processes.”
Now, when scientists have restricted the flow IN terms of, Sammons hopes to find more clues that will lead to a cause or mechanism of this event. One of the hypotheses that scientists want to study is the connection between the sudden and rapid appearance of oxygen and “Earth-snow”, a period when the continents and oceans of the Earth were mostly covered with ice.
In addition, you need to understand why these our 21% oxygen in the atmosphere remain stable for a long time.
Scientists said that oxygen first appeared in earth’s atmosphere
Ilya Hel