(ORDO NEWS) — About a fifth of our planet’s atmosphere is oxygen, an essential gas necessary for the existence of complex life forms.
Scientists believed that the main and practically the only source of it were living organisms – photosynthetic plants and bacteria. But now they may have to rethink their views.
The first photosynthetic organisms, cyanobacteria , appeared on Earth about three and a half billion years ago.
For a long time, scientists believed that living organisms served as almost the only source of free oxygen, which for almost three billion years did not accumulate in the atmosphere, but was absorbed by terrestrial rocks and sea water.
Now, however, researchers have found that at least some of the early oxygen may have come from another source.
Oxygen could enter the atmosphere from underground, as a result of movements and destruction of the earth’s crust.
On the current Earth, the plates of its crust are actively moving, and in subduction zones , some plates are submerged under others. But scientists are still arguing whether the same pattern was observed billions of years ago.
If yes, then of particular interest is the formation of oxidized magmas , in the creation of which oxidized bottom sediments and cold sea water participate.
Such magmas are distinguished by an increased content of water and oxygen, which are “stored” under the Earth’s surface for many years.
An international team of researchers decided to check whether traces of oxidation are present in Neoarchean granitoid rocks collected in Canada.
For greater accuracy, scientists studied the composition of zircon crystals contained in these rocks: they are the most resistant to environmental influences and help to clarify the conditions for the formation of the rock, as well as its age.
It turned out that about 2750 million years ago, the amount of oxidized sulfur increased in these rocks, which could only come there from an oxygen-containing source.
Since granitoid rocks are of igneous origin, this means that oxidized magmas were already forming under the crust of the Neoarchean Earth, and oxygen could be released into the atmosphere during volcanic eruptions.
So far, scientists cannot say where oxygen came from in the earth’s magma of that time, because there was still very little of it in the oceans.
Perhaps, in the process of subduction, oceanic water plunged deep into our planet, where water molecules were destroyed into hydrogen and free oxygen, and the latter was already oxidizing the overlying layers of magma.
Since the Earth is now the only celestial body in the solar system that has observed the movement of tectonic plates, new data may explain the lack of oxygen on other planets, not only orbiting the Sun, but also in other places in the universe.
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