Privileged Planet: when early oxygen appeared (Introduction)

by David Turell , Monday, February 25, 2019, 20:12 (2098 days ago) @ David Turell

Before the great oxygen event at 2.5 byo:

https://phys.org/news/2019-02-ancient-clues-earth-early-history.html

"By studying ancient rocks, researchers have determined that sometime between 2.5 and 2.3 billion years ago, Earth underwent what scientists call the "Great Oxidation Event" or "GOE" for short. O2 first accumulated in Earth's atmosphere at this time and has been present ever since.

"Through numerous studies in this field of research, however, evidence has emerged that there were minor amounts of O2 in small areas of Earth's ancient shallow oceans before the GOE.

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"Using mass spectrometers, the team measured the thallium and molybdenum isotope compositions of the Mt. McRae Shale. This was the first time both isotope systems had been measured in the same set of shale samples. As hypothesized, a predictable thallium and molybdenum isotope pattern emerged, indicating that manganese oxide minerals were being buried in the sea floor over large regions of the ancient ocean. For this burial to occur, O2 needed to have been present all the way down to the sea floor 2.5 billion-years-ago.

"These findings improve scientists' understanding of Earth's ocean oxygenation history. Accumulation of O2 was probably not restricted to small portions of the surface ocean prior to the GOE. More likely, O2 accumulation extended over large regions of the ocean and extended far into the ocean's depths. In some of these areas, O2 accumulation seems to have even extended all the way down to the sea floor.

"'our discovery forces us to re-think the initial oxygenation of Earth," states Ostrander.

"'Many lines of evidence suggest that O2 started to accumulate in Earth's atmosphere after about 2.5 billion years ago during the GOE. However, it is now apparent that Earth's initial oxygenation is a story rooted in the ocean. O2 probably accumulated in Earth's oceans—to significant levels, according to our data—well before doing so in the atmosphere."

"'Now that we know when and where O2 began to build up, the next question is why" says ASU President's Professor and co-author Anbar. "We think that bacteria that produce O2 were thriving in the oceans long before O2 began to build up in the atmosphere. What changed to cause that build-up? That's what we're working on next.'"

Comment: life first without oxygen, then living bacteria producing oxygen so the rest of the more complex organism could evolve. A stepwise process not by chance.