Geoscience Reference
In-Depth Information
The Bank of Time
Those Confounded Millions of Years
Even using their own methods to calculate the age of the Earth, geologists could
not escape Kelvin's influence. Each calculation from geology depended on its own
assumptions, and each gave at least a slightly different answer. How could an indi-
vidual calculator tell whether his result was anywhere close to right? In the second
half of the nineteenth century there was only one way, and that was to compare
one's result with that of the lone external authority: Lord Kelvin. The temptation
proved irresistible to the geological calculators, who “produced an amazing vari-
ety of methods and an even greater homogeneity of results.” 1
One of the first was John Phillips (1800-1874). “Nothing can be simpler in as-
pect than the problem of the age of the stratified crust of the globe on the Uniform-
itarian hypothesis,” he wrote in 1860. “We have only to find out the rate of accu-
mulation of sediment in the sea—the thickness of deposits produced in a year, or
century,orsomelonghistoricperiod—andapplythismeasureorratetotheancient
deposits.” 2 He reported that “the Ganges River delivers 1/111th of an inch of sedi-
ment in a year.” Geologists had estimated the maximum thickness of the sediments
in the Ganges Basin at 72,000 feet. Divide accumulation by rate, and you have the
“calculated antiquity of the base of the stratified rocks = 95,904,000 years.” 3
We might describe Phillips's method by analogy to an hourglass. If you know
the rate at which sand passes through the constriction, and you know the amount
of sand in the bottom of the hourglass, divide amount by rate and you have the
time elapsed since the hourglass was turned over. Or, instead of using the amount
of sand in the bottom, analogous to sedimentation, you could use the amount re-
maining in the top, analogous to erosion.
Phillips was well aware that his answer relied on several assumptions: that the
rate of sediment accumulation was accurately known, that it had not changed over
geologic time, and that erosion had not removed some of the accumulated sedi-
ments. Even making different assumptions, however, Phillips said that his result
“cannot be reduced to so little as 38,000,000 years” (136). He also noted that the
Ganges carries more sediment than other great rivers, so that his 96-million-year
estimate for the age of the Earth's crust “may be much too short” (126).
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