From Science News:
By carefully crushing rock salt, researchers have measured the chemical makeup of air pockets embedded inside the rock. This new technique reveals that oxygen made up 10.9 percent of Earth’s atmosphere around 815 million years ago. Scientists have thought that oxygen levels would not be that high until 100 million to 200 million years later. The measurements place elevated oxygen levels well before the appearance of animals in the fossil record around 650 million years ago, the researchers report in the August issue of Geology.
“I think our results will take people by surprise,” says study coauthor Nigel Blamey, a geochemist at Brock University in St. Catharines, Canada. “We came out of left field, and I think some people are going to embrace it, and other people are going to be very skeptical. But the data is what the data is.”
Scientists have previously measured ancient Earth’s oxygen supply by looking for the fingerprints of chemical reactions that require oxygen to take place (SN: 11/29/14, p. 14). Such work has suggested that oxygen levels rose sharply around 600 million years ago, during the Neoproterozoic era. More.
See also: Plate tectonics explains early Earth oxygen
All the theories of early Earth oxygen you can shake a stick at
The basic problem is that science is about measurement, and no one knows for sure how much oxygen there was on early Earth or how it changed over time. The debate is interesting and I don’t mind covering it, but it is a fruitless contention. But then, I have covered many fruitless contentions in other areas as well.
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