Carbon Dioxide Kept In Check

Land plants may have played a vital role in maintaining a consistent concentration of atmospheric CO₂ over the past 24 million years, helping to prevent Earth from freezing over, scientists report (Nature 2009, 460, 85). This CO₂ stability has been a mystery because of an inherent imbalance of two important geological processes. According to best estimates, the uptake of CO₂ during the weathering of silica-based minerals that occurs as mountain ranges grow should have far exceeded the CO₂ output from volcanic activity. Without some kind of balancing influence, a “runaway icehouse” effect stemming from declining CO₂ levels should have rendered Earth a frozen ball by now. Yale University’s Mark Pagani and colleagues suggest that the decline in plant growth that comes with lower CO₂ concentrations curbs the plants’ ability to weather rocks, thereby providing a negative-feedback system to keep CO₂ levels from falling too far.