Lessons from the Past?
The geological record is replete with extinction events, their intensity ranging from the small and local to global mass extinctions that shattered Earth's biological order. Inevitably, extinctions were followed by rediversification, directed in the case of the largest events by ecological reorganization. What can we learn from paleobiology, other than the oft-quoted observation that recovery proceeds slowly in the wake of grand scale biotic disruption (40, 53, 54)? Can we find generalities among extinction episodes that can guide thinking about our own future? Or, is it the differences among extinction events that should command our attention? As David Jablonski (63) asks in these proceedings, should we even focus on the five great mass extinctions that capture most attention, or do the more numerous, smaller events scattered throughout the geological record provide closer analogs for the present?
The geologic record contains much evidence of bounce-back processes (49, 54-59), but how far will these serve as analytic blueprints for what lies ahead? How can we estimate time frames at issue? Should we anticipate a minimum period of several million years [perhaps as much as 10 million (56)] before evolution can reestablish anywhere near the biological configurations and ecological circuitry existing before the current crisis? Will some recovery processes operate in some sectors of the biosphere, others in others, and with widely varying rates (55, 58, 60)?
In some major extinctions, for example the Cretaceous-Tertiary boundary event, environmental perturbation was swift and sure, but also short-lived. Recovery began soon after disruption. In the present biotic crisis, it is hard to envision a scenario under which the factors that are driving the biosphere toward grand scale biodiversity loss will be mitigated in the wake of such loss. On the contrary, on any time scale we can envisage (and any scenario that does not involve early mass mortality for humankind), the situation becomes bad and then stays bad for some time to come. Thus, on the time scale of the human species, environmental disruption (or at least aspects of it) is permanent. Under these circumstances (which may, to some degree, be approximated by the persistent environmental discord after the Permian-Triassic mass extinction), the prospects for rediversification are limited.
Answers to all your Biology Questions
