The appearance of oxygen in the Earth's atmosphere probably did not occur as a single event, but as a long series of starts and stops, according to geoscientists who investigated rock cores from the FAR DEEP project.
The Fennoscandia Arctic Russia - Drilling Early Earth Project--FAR DEEP--took place during the summer of 2007 near Murmansk in Northwest Russia.
The project, part of the International Continental Scientific Drilling Program, drilled a series of shallow, two-inch diameter cores and, by overlapping them, created a record of stone deposited during the Proterozoic Eon--2,500 million to 542 million years ago.
"We've always thought that oxygen came into the atmosphere really quickly during an event," said Lee Kump, a geoscientist at Penn State University.
"We are no longer looking for an event. Now we're looking for when and why oxygen became a stable part of the Earth's atmosphere."
The researchers report in this week's issue of the journal Science Express that evaluation of these cores, in comparison with cores from Gabon previously analyzed by others, supports the conclusion that the Great Oxidation Event, the appearance of free oxygen in Earth's atmosphere, played out over hundreds of millions of years. Kump is the lead author of the Science Express paper.
Oxygen levels gradually crossed the low atmospheric oxygen threshold for pyrite--an iron sulfur mineral--oxidation by 2,500 million years ago, and the loss of what scientists call mass-independently fractionated (MIF) sulfur by 2,400 million years ago.
Then oxygen levels rose at an ever-increasing rate through the Paleoproterozoic, achieving about one percent of the present atmospheric level.
"The definition of when an oxygen atmosphere occurred depends on which threshold you are looking for," said Kump. "It could be when pyrite becomes oxidized, when sulfur MIF disappears, or when deep crustal oxi
|Contact: Cheryl Dybas|
National Science Foundation