The Sixth Extinction: An Unnatural History

youngest—Tyrannosaurus rex teeth from the late Cretaceous—are farther
away. If you stand at the edge of the exhibit, which is really the only place
from which to view it, you are positioned right where the victims of the
Sixth Extinction should go.
In an extinction event of our own making, what happens to us? One
possibility—the possibility implied by the Hall of Biodiversity—is that we,
too, will eventually be undone by our “transformation of the ecological
landscape.” The logic behind this way of thinking runs as follows: having
freed ourselves from the constraints of evolution, humans nevertheless
remain dependent on the earth’s biological and geochemical systems. By
disrupting these systems—cutting down tropical rainforests, altering the
composition of the atmosphere, acidifying the oceans—we’re putting our
own survival in danger. Among the many lessons that emerge from the
geologic record, perhaps the most sobering is that in life, as in mutual
funds, past performance is no guarantee of future results. When a mass
extinction occurs, it takes out the weak and also lays low the strong. V-
shaped graptolites were everywhere, and then they were nowhere.
Ammonites swam around for hundreds of millions of years, and then they
were gone. The anthropologist Richard Leakey has warned that “Homo
sapiens might not only be the agent of the sixth extinction, but also risks
being one of its victims.” A sign in the Hall of Biodiversity offers a quote
from the Stanford ecologist Paul Ehrlich: IN PUSHING OTHER SPECIES TO
EXTINCTION, HUMANITY IS BUSY SAWING OFF THE LIMB ON WHICH IT PERCHES.
Another possibility—considered by some to be more upbeat—is that
human ingenuity will outrun any disaster human ingenuity sets in
motion. There are serious scientists who argue, for instance, that should
global warming become too grave a threat, we can counteract it by
reengineering the atmosphere. Some schemes involve scattering sulfates
into the stratosphere to reflect sunlight back out to space; others involve
shooting water droplets over the Pacific to brighten clouds. If none of this
works and things really go south, there are those who maintain people
will still be OK; we’ll simply decamp to other planets. One recent book