Sources of this oxygen are intended for publication available at Natural Earth Sciences. The basic conclusion in this case is that some of the oxygen that appeared on the young Earth was of tectonic origin. As the plates that make up our planet’s crust shifted, they were damaged and oxygen was released into the atmosphere.
The dominant tectonic activity today is plate tectonics, which causes oceanic crust to collapse into the Earth’s mantle at points called subduction zones. It is debatable whether similar events occurred in the Archean Era, an eon that lasted roughly 4 to 2.5 billion years.
It is also known that one of the features of today’s subduction zones is the occurrence of oxidative magma. This forms when oxidized sediment and dense cold water near the ocean floor enter the Earth’s mantle. As a result, igneous rocks with a high oxygen and water content are formed. If similar structures existed in the distant past, this indicates the possibility of subduction zones and plate tectonics some 2.7 billion years ago.
Oxygen probably appeared in Earth’s atmosphere about 2.7 billion years ago
By collecting samples in North America, scientists have been able to assess magma oxygenation from this period. Their particular attention was drawn to apatite, a mineral found in zircon crystals. They are very durable and long-lived, so they can be a kind of time capsules that provide information about this phenomenon from billions of years ago.
Apatite crystals are 30 microns wide, that is, they correspond to the size of human skin cells. Because it contains sulfur, by measuring its amount, researchers can answer a key question: Did apatite form from oxidized magmas? While the sulfur content was initially essentially zero, it increased to about 2,000 ppm about 2,705 million years ago. Rule? Igneous rocks became richer in sulfur.
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Moreover, the lack of dissolved oxygen in the Arche basins did not prevent the formation of sulfur-rich oxidised igneous rocks in the subduction zones. The oxygen in these regions must have come from a different source, eventually finding its way into the atmosphere during volcanic eruptions.
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