The proportion of oxygen in the Earth’s atmosphere remained extremely low after the appearance of the first photosynthetic microbes because the rocks of the ancient continents actively absorbed its molecules, preventing them from accumulating in the ocean and air, according to an article published in the journal Nature Geoscience.
“The saturation of the Earth’s atmosphere with oxygen could occur at any time, and all that was needed was the” right “chemical composition of the continents.We discovered that the chemical composition of the continents changed dramatically at the very time when oxygen began to accumulate in the primary ocean waters of the planet “Says Matthijs Smit of the University of British Columbia in Vancouver, Canada.
As scientists believe today, the Earth in the distant past had little to do with itself today – in its atmosphere there was no oxygen and there was a lot of carbon dioxide and methane. Its waters, reminiscent of the temperature and consistency of boiling thick soup, were inhabited by bizarre extremophile bacteria, traces of which in the form of deposits of peculiar “blankets” from the colonies of microbes, scientists often find in the oldest rocks of the Earth.
When exactly life was born, while nobody knows – there is conflicting evidence that it existed already 3.3-3.7 billion years ago or even 4 billion years ago, virtually immediately after the completion of the formation of the Earth and the moon and the end of their “bombardment” large asteroids and comets, which brought the “bricks of life” to Earth.
This life, as Smith tells, existed before the event, which geologists call the “great oxygen disaster.” Approximately 2.4-2.32 billion years ago, the oxygen concentration in the atmosphere rose sharply, rising from 0.0001% to 21% today. The cause of its appearance today are the first photosynthetic organisms, cyanobacteria, which cleared the atmosphere of CO2 and filled it with oxygen.
On the other hand, as the scientists note, it remains unclear what exactly inhibited the growth of oxygen concentration in water and in the Earth’s atmosphere in those hundreds of millions of years when cyanobacteria already existed in the primary ocean of the planet.
Some scientists suggest that the “extra” oxygen was absorbed by the primary continental rocks of the Earth formed at a time when there was practically no oxygen in its atmosphere, while others believe that the remains of living organisms that accumulated on the bottom took the role of the “absorber” of oxygen Earth’s oceans are hundreds of millions of years old.
Smith and his colleague Klaus Mezger from the University of Bern in Switzerland found new evidence in favor of the first hypothesis by analyzing the chemical composition of tens of thousands of cortical samples formed long before the onset of the “oxygen disaster” and at a time when the proportion of oxygen in the atmosphere grew at the maximum rate.
For this analysis, scientists used an ingenious technique – they measured the proportions of chromium and uranium in these rocks, reacting differently to the process of destruction of rocks by oxygen and water. Accordingly, the more these differences, the longer and stronger the elements acted on these rocks, which allows us to understand what role the continents of the Earth played in the appearance of its oxygen reserves.
As shown by these measurements, the proportions of chromium and oxygen in continental rocks began to change approximately three billion years ago, which coincides with the appearance of the first photosynthetic organisms. Approximately 300 million years before the “oxygen disaster”, their proportion varies dramatically, indicating a similarly sharp change of one type of rock to another, almost not absorbing oxygen. This is what scientists believe was the reason for the beginning of the “oxygen disaster” that dramatically changed the face of the Earth and its first inhabitants and made it suitable for the existence of man and other modern living beings.