Widespread volcanic activity, cyanobacteria and global glaciation may sound like the plot of a new, blockbuster disaster movie, but in reality, they are all events in the mystery surrounding the development of our oxygen-rich atmosphere, according to a Penn State geoscientist.
The most extreme fluctuation in the Earths carbon cycle occurred about 2.2 billion years ago, according to Dr. Lee R. Kump, professor of geosciences and member of the Penn State Astrobiology Research Center, and the conventional explanation is that it marks the debut of our oxygen atmosphere. Recently, however, better geological dating and a better proxy measure of when oxygen occurred in the atmosphere suggest that the oxygen atmosphere appeared long before this supposedly seminal event. "The new dating and proxy clearly show that the rise of oxygen preceded its apparent cause by at least 100 million years," Kump told attendees at the Geological Society of America conference Nov. 8 in Denver.
The proxy measure of when significant oxygen appeared in the atmosphere is sulfur. In an oxygen atmosphere, which is very oxidizing, all sulfur eventually becomes sulfate, but in a reducing atmosphere – one without significant oxygen – sulfur deposits as sulfate, sulfite or even pure sulfur and retains an unusual isotopic signature of upper atmospheric processes. Better dating of these strange isotopes in rocks found them to be 2.3 billion years old or older and does suggest that oxygen appeared earlier than the carbon cycle perturbation.
Andrea Elyse Messer | EurekAlert!
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