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heat flow, most notably by Clarence King, director of the Geological Survey
of Canada. King, using Kelvin's methodology, arrived at an even lower esti-
mate than Kelvin's; he calculated that the earth was only 24 million years old.
The Kelvin-King conclusions regarding the age of the earth were
widely but not universally accepted. The chief dissenters were those familiar
with evolution and the fossil record—such as Darwin's "bulldog," Thomas
Huxley—and those who studied the rate at which sedimentary rocks accu-
mulate. Twenty-four million years was far too short a time to accommodate
all of the evolutionary changes visible in the fossil record, and it was also too
short to account for the amount of sedimentary rock present on the earth's
surface. With regard to the latter, in 1895 the geologist William Sollas esti-
mated that thickness to be more than 100,000 meters, if it were to be piled
upward in one continuous column. A column of sediment 60 miles tall, sit-
ting on the surface of the earth, would certainly take time to form, assuming
that the processes (and rates) of sedimentary rock accumulation have been
uniform through time. Sollas then asked the following question: What
is
the
rate at which sedimentary rocks, past and present, can be expected to accu-
mulate? He assumed that sedimentary rocks accumulate at a rate of about 1
meter each 300 years and thus arrived at an estimate of about 34 million
years for the age of the earth since sedimentation began. This figure was very
much a
minimum,
for it assumed that the sedimentary rocks accumulated
without pause or break. In fact, however, most sedimentary rocks accumulate
in sporadic fashion, and there may be long periods of time when no sedi-
ments accumulate. Furthermore, the Sollas estimate did not account for the
long stretch of time that passed, because of the eatth's eatly, molten surface,
before sedimentation even began.
A mote ingenious attempt to arrive at a reliable estimate of earth's age
came to be known as the "salt clock." The amount of salt in the ocean, and
the tate at which it arrived there, were thought to offer a way of calculating
the age of the earth. Using this method, several chemists arrived at an esti-
mate of about 100 million years.
By the eatliest part of the twentieth century, physicists, chemists, and
geologists had reached consensus on a figure of between 25 and 100 million
