New Oxygen research;great oxygenation event study (Introduction)

by David Turell , Monday, September 18, 2017, 23:11 (2622 days ago) @ David Turell

The level of atmospheric oxygen was kept low by the Earth's surface mineral, Olivine, until it disappeared:

https://www.sciencedaily.com/releases/2017/09/170918111851.htm

"Earth's early atmosphere and oceans were devoid of free oxygen, even though tiny cyanobacteria were producing the gas as a byproduct of photosynthesis. Free oxygen is oxygen that isn't combined with other elements such as carbon or nitrogen, and aerobic organisms need it to live. A change occurred about three billion years ago, when small regions containing free oxygen began to appear in the oceans. Then, about 2.4 billion years ago, oxygen in the atmosphere suddenly increased by about 10,000 times in just 200 million years.
This period, known as the Great Oxidation Event, changed chemical reactions on the surface of the Earth completely.

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"It turned out that a staggering change occurred in the composition of continents at the same time free oxygen was starting to accumulate in the oceans," Smit said.

"Before oxygenation, continents were composed of rocks rich in magnesium and low in silica -- similar to what can be found today in places like Iceland and the Faroe Islands. But more importantly, those rocks contained a mineral called olivine. When olivine comes into contact with water, it initiates chemical reactions that consume oxygen and lock it up. That is likely what happened to the oxygen produced by cyanobacteria early in Earth's history.

"However, as the continental crust evolved to a composition more like today's, olivine virtually disappeared. Without that mineral to react with water and consume oxygen, the gas was finally allowed to accumulate. Oceans eventually became saturated, and oxygen crossed into the atmosphere.

"It really appears to have been the starting point for life diversification as we know it," Smit said. "After that change, the Earth became much more habitable and suitable for the evolution of complex life, but that needed some trigger mechanism, and that's what we may have found."

"As for what caused the composition of continents to change, that is the subject of ongoing study. Smit notes that modern plate tectonics began at around the same time, and many scientists theorize that there is a connection."

Comment: Oxygen in high amounts must be present for life to evolve and diversify. It first rose to about 10% before the Cambrian and finally reached its present 21%. This shows how the Earth had to evolve for complex life to appear.