Washington, April 30 : A new study has suggested that before the era of fossil fuels, the carbon dioxide (CO2) in the atmosphere was checked by Earth's minerals.
Carried out by researchers from the University of Hawaii and Carnegie Institution, the study links the pre-human stability to connections between carbon dioxide in the atmosphere and the breakdown of minerals in the Earth's crust.
While the process occurs far too slowly to have halted the historical buildup of carbon dioxide from human sources, the finding gives scientists new insights into the complexities of the carbon cycle.
Fort he research, Ken Caldeira of the Carnegie Institution's Department of Global Ecology and Richard Zeebe of the University of Hawaii studied levels of carbon dioxide in the atmosphere over the past 610,000 years using data from gas bubbles trapped in Antarctic ice cores.
They used these records, plus geochemical data from ocean sediments, to model how carbon dioxide released into the atmosphere by volcanoes and other natural sources is ultimately recycled via carbon-bearing minerals back into the crust.
According to the study, when carbon dioxide levels in the atmosphere rise, the chemical reactions that break down silicate minerals in soils are accelerated.
Among the products of these reactions are calcium ions, which dissolve in water and are washed to the ocean by rivers. Marine organisms such as mollusks combine the calcium ions with dissolved carbon dioxide to make their shells (calcium carbonate), which removes both calcium and carbon dioxide from the ocean, restoring the balance.
The researchers found that over hundreds of thousands of years, the equilibrium between carbon dioxide input and removal was never more than one to two percent out of balance, a strong indication of a natural feedback system.
This natural feedback acts as a thermostat, which is critical for the long-term stability of climate.
During Earth's history, it has probably helped to prevent runaway greenhouse and icehouse conditions over time scales of millions to billions of years - a prerequisite for sustaining liquid water on the planet's surface.
"The system is finely in tune," said Caldeira. "That one or two percent imbalance works out to an average imbalance in natural carbon dioxide emissions that is thousands of times smaller than our current emissions from industry and the destruction of forests," he added.
Previous researchers had suggested that such a system existed, but the new study provides the first observational evidence supporting the theory, and confirms its role in stabilizing the carbon cycle.