The Sixth Extinction: An Unnatural History

it moved and incinerating anything in its path. “Basically, if you were a
triceratops in Alberta, you had about two minutes before you got
vaporized” is how one geologist put it to me.
In the process of excavating the enormous crater, the asteroid blasted
into the air more than fifty times its own mass in pulverized rock. As the
ejecta fell back through the atmosphere, the particles incandesced,
lighting the sky everywhere at once from directly overhead and
generating enough heat to, in effect, broil the surface of the planet. Owing
to the composition of the Yucatán Peninsula, the dust thrown up was rich
in sulfur. Sulfate aerosols are particularly effective at blocking sunlight,
which is the reason a single volcanic eruption, like Krakatoa, can depress
global temperatures for years. After the initial heat pulse, the world
experienced a multiseason “impact winter.” Forests were decimated.
Palynologists, who study ancient spores and pollen, have found that
diverse plant communities were replaced entirely by rapidly dispersing
ferns. (This phenomenon has become known as the “fern spike.”) Marine
ecosystems effectively collapsed, and they remained in that state for at
least half a million, and perhaps as many as several million, years. (The
desolate post-impact sea has been dubbed the “Strangelove ocean.”)
It’s impossible to give anything close to a full account of the various
species, genera, families, and even whole orders that went extinct at the
K-T boundary. On land, every animal larger than a cat seems to have died
out. The event’s most famous victims, the dinosaurs—or, to be more
precise, the non-avian dinosaurs—suffered a hundred percent losses.
Among the groups that were probably alive right up to the end of the
Cretaceous were such familiar museum shop fixtures as hadrosaurs,
ankylosaurs, tyrannosauruses, and triceratops. (The cover of Walter
Alvarez’s book on the extinction, T. Rex and the Crater of Doom, shows an
angry-looking tyrannosaurus reacting with horror to the impact.)
Pterosaurs, too, disappeared. Birds were also hard-hit; perhaps three-
quarters of all bird families, perhaps more, went extinct. Enantiornithine
birds, which retained such archaic features as teeth, were wiped out, as