Ground to Air: Ancient Rocks Reveal a Massive Carbon Shift

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Did carbon releases tip the climate from cold to balmy? Image Credit: Arinas

For billions of years, the weather has been a hot topic.  Perhaps early organisms chatted about it as they passed each other in the primeval seas. In recent decades, the climate and the composition of the earth’s atmosphere have also become popular dinner table and conference conversation, as evidenced by the current discussions that swirl around the viability of the Kyoto Accord.

A study released today focuses our attention on the small, cumulative changes that can lead to huge swings in the planet’s atmospheric and climatic systems. Some have called humans a ‘god’ species. But are we the only ones who have played with the planet’s atmosphere, causing massive change? Of course not. We’re just the only ones that we remember.

The planet seems slow and unwieldy, but it is a complex system that can tip from one extreme to another. The key to one such shift is found in two billion year old Russian rocks. Scientists at Penn State acquired 3600 meters of drill core from the Russian Arctic. These rocks formed during the time when the earth’s atmosphere was becoming rich in oxygen, suitable for the growth of eukaryotic organisms. As they did routine carbon isotope studies on the rocks, Lee Kump and his colleagues discovered that they told the story of massive change in the earth’s carbon balance.

The story begins in the carbon deposits located in sedimentary rocks. As the earth moves mountain ranges upward, the sedimentary rocks move up, erode, and are exposed to the air. The rocks react with oxygen in the air, and this reaction releases carbon dioxide.

Rising oxygen levels triggered mass oxidation of sedimentary rocks. Image Credit: dyet

But before there was an oxygen-rich atmosphere, the carbon simply accumulated in the rocks. It was only when early organisms started to make large quantities of oxygen that the atmosphere gradually became more oxygen-rich. Kump speculates that the rising levels of oxygen destroyed much of the methane in the atmosphere. Methane is a greenhouse gas, so when much of it was lost, the earth cooled.

Into the atmosphere of an ice-covered earth came even more oxygen from early organisms. When levels hit perhaps one percent of today’s levels, another shift happened, this time one that may have warmed the earth. Oxygen levels became high enough to trigger the oxidation of all that rock-bound carbon. All of the carbon in the rocks reacted in the same time frame, releasing a massive amount of carbon into the atmosphere.

What happened next? According to Dr Kump, that is still a bit of a mystery. At the time, the earth was covered in glaciers. After the oxidation event, the earth warmed.  While a warmer earth might seem more conducive to life, the inflow of carbon into the atmosphere would have changed the balance of atmospheric gases, making life tough for oxygen-loving prehistoric organisms.

Kump told Decoded Science that while the focus of the study was atmospheric oxygen levels, the discovery of a huge shift in carbon levels shows how “the Earth is a tightly coupled system involving atmosphere, ocean, land, and life that evolves through a series of events, often triggered by the passage of thresholds (tipping points) that are difficult to predict and thus always a bit of a surprise.” For those who love to tinker with the atmosphere and therefore the climate, the idea of triggers and sudden shifts can be frightening. Although the study of 2 billion year old rocks might not seem to be relevant to climate and atmospheric science today, it is well worth a sober look.

References

Kump, L. R., Junium, C., Arthur, M. A., Brasier, A., Fallick, A., Melezhik, V., Lepland, A., Črne, A. E., Luo, G. Isotopic Evidence for Massive Oxidation of Organic Matter Following the Great Oxidation Event. Science. December 1, 2011. Accessed December 1, 2011.

Personal Interview. Lee R. Kump. November 29, 2011.

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