Not the end, but the beginning of the world as we know it

November 08, 2004

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 Earth's 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 today (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.

If the large carbon marine sequestration episode does not coincide with the increase of oxygen, what does? Cyanobacteria -- marine organisms that are photosynthetic - produced oxygen during these early pre-oxygen atmosphere years. However, because the atmosphere was heavily reducing, the oxygen was quickly removed from the atmosphere.

The shift from a reducing atmosphere to an oxidizing one occurred when volcanic activity gradually switched from volcanoes that outgas hydrogen and carbon monoxide to those that produce water vapor and carbon dioxide, according to Kump. These mantle plume volcanoes bring molten rock up from deep within the earth.

With larger amounts of water and carbon dioxide in the atmosphere, hydrogen and carbon monoxide were no longer using up all the oxygen produced by the Cyanobacteria and the amounts of oxygen increased. In a few million years, the oxygen levels reach those of Earth's atmosphere today.

"The increases and mantle plume changes came in pulses, not all at once," says Kump. "There was a step wise increase first at 2.7 billion years ago and then at 2.4 billion years ago."

As the oxygen built up, iron rich layers called red beds, because the iron is oxidized to rust, were deposited around the world. Redbeds are considered a sign of atmospheric oxygen.

But also, as the oxygen increased, the levels of methane decreased.

"You can have a methane-rich atmosphere with a little oxygen or an oxygen-rich atmosphere with a little methane, but both cannot be high," says Kump. "Methane was the most important greenhouse gas left in the atmosphere."

Without greenhouse gases and in the presence of a faint young Sun that produced less heat than the Sun does today, the Earth cooled, according to a theory published earlier by Penn State colleagues James Kasting and Alexander Pavlov. Glaciation on a global scale followed. However, the volcanoes continued to produce carbon dioxide - a greenhouse gas - until the atmosphere warmed enough to melt the glaciers.

"We have found really oxidized basalt, which is anomalous, in Northern Russia near Scandinavia. This basalt would be a very poor sponge for soaking oxygen out of the atmosphere," says Kump. "We need to look for more evidence of these oxygen producing mantle rocks."
-end-
NASA's Astrobiology Institute funded this research.

Penn State

Related Greenhouse Gas Articles from Brightsurf:

Make your own greenhouse gas logger
Researchers at Linköping University's Department of Thematic Studies, Environmental Change, have developed a simple logger for greenhouse gas flows.

Old carbon reservoirs unlikely to cause massive greenhouse gas release
As global temperatures rise, permafrost and methane hydrates -- large reservoirs of ancient carbon -- have the potential to break down, releasing enormous quantities of the potent greenhouse gas methane.

Mediterranean rainfall immediately affected by greenhouse gas changes
Mediterranean-type climates face immediate drops in rainfall when greenhouse gases rise, but this could be interrupted quickly if emissions are cut.

Seeking better guidelines for inventorying greenhouse gas emissions
Governments around the world are striving to hit reduction targets using Intergovernmental Panel on Climate Change (IPCC) guidelines to limit global warming.

Nitrous oxide, a greenhouse gas, is on the rise
A new study from an international group of scientists finds we are releasing more of the greenhouse gas nitrous oxide into the atmosphere than previously thought.

Atmospheric pressure impacts greenhouse gas emissions from leaky oil and gas wells
Fluctuations in atmospheric pressure can heavily influence how much natural gas leaks from wells below the ground surface at oil and gas sites, according to new University of British Columbia research.

Natural-gas leaks are important source of greenhouse gas emissions in Los Angeles
Liyin He, a Caltech graduate student, finds that methane in L.A.'s air correlates with the seasonal use of gas for heating homes and businesses

From greenhouse gas to fuel
University of Delaware scientists are part of an international team of researchers that has revealed a new approach to convert carbon dioxide gas into valuable chemicals and fuels.

UBC researchers explore an often ignored source of greenhouse gas
In a new study from UBC's Okanagan campus, researchers have discovered a surprising new source of carbon dioxide (CO2) emissions -- bicarbonates hidden in the lake water used to irrigate local orchards.

Corncob ethanol may help cut China's greenhouse gas emissions
A new Biofuels, Bioproducts and Biorefining study has found that using ethanol from corncobs for energy production may help reduce greenhouse gas emissions in China, if used instead of starch-based ethanol.

Read More: Greenhouse Gas News and Greenhouse Gas Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.