22
I
n the early days of studying
fossils, many people denied
they could be extinct species.
They failed to see why God would
create and destroy creatures before
humans ever appeared, arguing
that unfamiliar fossil species might
still be living somewhere on Earth.
In the late 18th century, French
zoologist Georges Cuvier looked
into this by exploring the anatomy
of living and fossil elephants. He
proved that fossil forms such as
mammoths and mastodons were
anatomically distinct from living
elephants, so they must represent
extinct species. (It was highly
unlikely that they still lived on
Earth without being noticed.)
Cuvier believed that Earth had
experienced a series of distinct
ages, each of which ended with a
“revolution” that destroyed existing
flora and fauna. He did not, though,believe that the evidence of fossil
remains supported a theory of
evolution. Nevertheless, Cuvier’s
central views have continued to
win support, and modern evidence
points to at least five catastrophic
mass extinction events in Earth’s
past, including the one that wiped
out the dinosaurs. Unlike Cuvier,
however, today’s scientists know
that life is not recreated out of
nothing after a catastrophe. Rather,
when a mass extinction event kills
off many species, those left will
evolve and multiply—sometimes
relatively quickly—to fill vacant
ecological niches, as the mammals
did after the age of the dinosaurs. ■A WORLD PREVIOUS
TO OURS, DESTROYED
BY CATASTROPHE
EXTINCTION AND CHANGE
IN CONTEXT
KEY FIGURE
Georges Cuvier (1769 –1832)BEFORE
Late 1400s Leonardo da Vinci
argues that fossils are the
remains of living creatures,
not just shapes spontaneously
formed in the earth.1660s English scientist Robert
Hooke suggests that fossils are
extinct creatures, since no
similar forms can be found
on Earth today.AFTER
1841 English anatomist
Richard Owen calls huge
reptile fossils “dinosaurs.”1859 Charles Darwin’s On the
Origin of Species explains how
evolution can occur through
“natural selection.”1980 US scientists Luis
and Walter Alvarez present
evidence that an asteroid
hit Earth at the time of the
extinction of the dinosaurs.Cuvier coined the name “mastodon”
for its Greek meaning of “breast tooth,”
referring to the nipplelike patterns on
the creature’s teeth, which were unlike
those of any living elephants.See also: Evolution by natural selection 24–31 ■ Ecological niches 50–51
■ An ancient ice age 198–199 ■ Mass extinctions 218–223US_022-023_Extinction_and_Change_Uniformitarianism.indd 22 12/11/18 6:24 PM