Earth System Stability Through Geologic Time

Abstract:

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 significant environmental
change recorded in the carbon-isotopic composition of sedimentary
rocks. There are also many such environmental events in the geologic
record that are not associated with mass extinctions. What makes them
different? Two factors appear important: the size of the
environmental perturbation, and the time scale over which it occurs.
We show that the natural perturbations of Earth's carbon cycle during the
past 500 million years exhibit a characteristic rate of change over
two orders of magnitude in time scale. This characteristic rate is
consistent with the maximum rate that limits quasistatic (i.e., near
steady-state) evolution of the carbon cycle. We identify this rate with
marginal stability, and show 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.