Ice core analyses indicates atmospheric oxygen levels have fallen 0.7 percent over the past 800,000 years

September 23, 2016 by Bob Yirka, Phys.org report
Credit: NASA/JSC Gateway to Astronaut Photography of Earth

(Phys.org)—A small team of researchers with Princeton University has found evidence that suggests that the amount of oxygen in the Earth's atmosphere has dropped by 0.7 percent over the past 800,000 years. In their paper published in the journal Science, the team describes their analyses of ice core samples taken from Antarctica and Greenland and offer some possible explanations for what they found.

Scientists have suspected that have fallen over the past million years or so, but have not been able to prove it, or even to offer reasonable estimates as to how much has taken place. They would like to know more about the history of oxygen levels because they have been tied very closely to life evolving on the planet and because they have had such a big impact on geochemical cycles—learning more about its history might offer clues about the future. In this new effort, the researchers sought to offer more concrete evidence. They studied a number of ice core samples that contained trapped representing air samples going back almost a million years.

In studying their data, the researchers found that had fallen by 0.7 percent over the past 800,000 years—they also calculated that oxygen sinks had removed approximately 1.7 percent more oxygen over that time period than sources had added. They also point out that the change is not a cause for alarm, noting that the difference is equivalent to riding an elevator to the 30th floor of a skyscraper.

The researchers suggest there are two possible reasons for the drain of oxygen. The first is that erosion around the globe has exposed more pyrite and organic compounds—prior research has found that both react with oxygen, causing it to be pulled from the air. The second possibility is a cooling ocean driving more oxygen-consuming microbe activity. They acknowledge that it could be something else entirely and suggest that more research needs to be done—they also suggest that a better understanding of what made our planet habitable may help us in finding others out there in space.

Explore further: Scientists measure the air breathed by Earth's first animals

More information: D. A. Stolper et al. A Pleistocene ice core record of atmospheric O2 concentrations, Science (2016). DOI: 10.1126/science.aaf5445

Abstract
The history of atmospheric O2 partial pressures (PO2) is inextricably linked to the coevolution of life and Earth's biogeochemical cycles. Reconstructions of past PO2 rely on models and proxies but often markedly disagree. We present a record of PO2 reconstructed using O2/N2 ratios from ancient air trapped in ice. This record indicates that PO2 declined by 7 per mil (0.7%) over the past 800,000 years, requiring that O2 sinks were ~2% larger than sources. This decline is consistent with changes in burial and weathering fluxes of organic carbon and pyrite driven by either Neogene cooling or increasing Pleistocene erosion rates. The 800,000-year record of steady average carbon dioxide partial pressures (PCO2) but declining PO2 provides distinctive evidence that a silicate weathering feedback stabilizes PCO2 on million-year time scales.

Related Stories

Humble moss helped create our oxygen-rich atmosphere

August 15, 2016

The evolution of the first land plants including mosses may explain a long-standing mystery of how Earth's atmosphere became enriched with oxygen, according to an international study led by the University of Exeter.

Rust under pressure could explain deep Earth anomalies

June 8, 2016

Using laboratory techniques to mimic the conditions found deep inside the Earth, a team of Carnegie scientists led by Ho-Kwang "Dave" Mao has identified a form of iron oxide that they believe could explain seismic and geothermal ...

Recommended for you

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Bongstar420
not rated yet Sep 25, 2016
Interesting..but since it "doesn't" have anything to do with global warming, it doesn't warrant any attention from the public.

Or any one hardly at all for that matter. lol

It would seem the average CO2 levels are declining slightly as well (not including the last 500 years). Much of the decline seems in the pre 80k years time.Current levels are significantly higher than the last 100k years average, almost certainly mostly from burning fossil fuels and farming.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.