The (Once Slow) Decline of Atmospheric Oxygen

4 Nov

Atmospheric oxygen has been decreasing at a relatively rapid rate.

Photo: Shutterstock

Oxygen is not only important to life, it has a great impact on evolution. Previous eras in the Earth’s history have had more atmospheric oxygen than we do now, and that contributed to the life that formed. Dinosaurs, for example, lived in an era with more oxygen, which contributed to their ability to grow so large. Now, very large land animals are rare.

A recent study of ice cores from Greenland has helped scientists determine atmospheric oxygen levels over the last 800,000 years. Over that time, oxygen levels decreased by 0.7 percent. Geologists say this is a pretty standard pace. However, within the last 100 years oxygen rates have declined by 0.1 percent, far faster than normal.

The cause of the rapid oxygen decline is the rampant use of fossil fuels, which puts too much carbon dioxide in the atmosphere.

“The planet has various processes that can keep carbon dioxide levels in check,” says Daniel Stolper, a postdoctoral research associate in Princeton University’s Department of Geosciences.

One of these is called silicate weathering. Carbon dioxide reacts with exposed rock to produce calcium carbonate. This traps carbon dioxide in solid form. The researchers have a hypothesis that as temperatures rise due to an increase in carbon dioxide, silicate weathering rates also increase.

Other carbon dioxide removal methods include plant respiration and sequestering it in water or soil.

Those processes for sequestering carbon that worked alongside the 0.7 percent decrease in oxygen, had a much longer timetable in which to work, but now they can’t keep up with humankind.

“The earth can take care of extra carbon dioxide when it has hundreds of thousands or millions of years to get its act together,” says study co-author John Higgins, an assistant professor of geosciences at Princeton University. “In contrast, humankind is releasing carbon dioxide today so quickly that [these processes] can’t possibly respond fast enough.”

Will this new research solve the problem? No, but knowing more about the rate at which the atmosphere naturally changes could help us to better understand how that process is changing the world we currently live in.

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