Earth-System Stability Through Geologic Time

Daniel Rothman

Lorenz Center, Department of Earth, Atmospheric, and Planetary Sciences, MIT




Five times in the past 500 million years, mass extinctions have resulted in the loss of greater than three-fourths of living species. Each of these events is associated with a significant perturbation of Earth's carbon cycle. But there are also many such environmental events in the geologic record that are not associated with mass extinctions. What makes them different? We show that natural perturbations of carbon cycle exhibit a characteristic rate of change consistent with the cycle's maximum rate of quasistatic evolution. We identify this rate with marginal stability, and find that mass extinctions occur on the fast, unstable side of the stability boundary. These results suggest that the great extinction events of the geologic past, and potentially a "sixth extinction" associated with modern environmental change, are characterized by common mechanisms of instability.