How Geologists Tell Time:
One of the factors that confronted Darwin when he
was formulating his ideas about natural selection was the amount of
time that it would require for change to accumulate to the point that
new species could evolve. The Victorian view of the age of the Earth
was based on estimates derived from interpretations of scripture by
Archbishop Ussher, who in 1654 proclaimed that the Earth was formed on
October 23rd, 4004 B.C. While Darwin was developing his thoughts
about natural selection, geologists were refining their calculations
for the age of the Earth. How did scientists determine that
the Earth was, in fact, many millions of years older than this, and
that therefore there was enough time for the processes of natural
selection to occur?
Photographs courtesy of the University of California Museum of
Paleontology: (http://evolution.berkeley.edu/)