Geoscience Reference
In-Depth Information
lations of Kelvin and King, arriving at an age of 60 million years. Even “with bet-
ter data,” he avowed, “this age will not be changed by more than perhaps 5 million
years.” Granting the physicists no quarter, in another paper that same year Becker
wrote that although “geologists would assuredly rejoice in the discovery of a valid
method” of measuring rock ages, “one condition of acceptance would clearly be
that it should give periods of the same order of magnitude as is indicated by purely
of geology.
By the teens, in contrast to Becker and Joly, other prominent geologists, includ-
ing Thomas Chamberlin, had begun to reconcile ages calculated from geologic
evidence with the ages calculated from radioactivity. One of the most influential
wasJosephBarrell(1869-1919),astructuralgeologistatYale.Ina143-pagepaper
in 1917, Barrell explained why the geological hourglasses had given false results.
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First, the rates of erosion and sedimentation throughout geological time had var-
ied greatly. Second, since today's rate of erosion is believed to be higher than the
long-term average, geologic processes appear to have run faster in the past than
they actually had. Third, the rate of erosion and the rate of sedimentation have not
been equal, as the hourglass calculators had assumed. Fourth and fatally, gaps rep-
resenting unknown amounts of time riddle the sedimentary record. (A fifth reason
isthatnineteenth-century geologists hadnowayofknowingthatPrecambrian time
accounts for nearly 90 percent of all geologic time.)
For such reasons, Barrell wrote, “Geologic time is certainly much
longer—perhaps ten or fifteen times longer—than the estimates based on a strictly
uniformitarian interpretation” (749). An earlier generation of geologists, “feeling
the need of meeting the demands of the physicists,” he wrote, had with difficulty
compressed their estimates into the range allowed by Kelvin and his followers.
Now with the advent of radioactivity, a new crop of “physicists destroy[ed] the
conclusions previously built by physicists” and “granted upwards of
1,500,000,000” years (749). “Many geologists,” Barrell wrote, “adjusted to the
previous limitations, shook their heads in sorrow and indignation at the new pro-
mulgations of this dictatorial hierarchy of exact scientists” (749).
He said that the evidence from radioactivity showing that as much as 500 milli-
onyearsmighthaveelapsed sincetheCambrian periodbeganwas“notinconflict”
brian time, it seemed probable to Barrell that “the oldest known rocks are as much
as 1,400,000,000 years of age” (881).
A Precocious Young Man
