The Bank of Time - Four Revolutions in the Earth Sciences - page 13

Another who attempted the hourglass method was none other than Charles Dar-
win (1809-1882), who ever after regretted the attempt. Darwin was a disciple of
Lyell, whose monumental Principles of Geology he had taken with him aboard the
Beagle . Later Darwin wrote: “He who can read Sir Charles Lyell's grand work
on the Principles of Geology, which the future historian will recognize as having
produced a revolution in natural science, and yet does not admit how vast have
been the past periods of time, may at once close this volume.” 4 Lyell repeatedly
referred to geologic time as “indefinite,” thus allowing plenty for natural selection
and evolution.
In the first edition of Origin of Species , Darwin fell prey to one of those im-
pulses that writers give into in a weak moment but as soon as they witness their
idea in print wish they had resisted. Darwin offhandedly threw in a calculation of
how long it had taken erosion to excavate a valley in southern England called the
Weald. He estimated the rate of erosion at “one inch per century,” a rotund num-
ber that has the feel of an educated guess—or possibly just a guess. Estimating the
amount of rock that erosion had removed to leave the Weald as we find it today,
and dividing by the rate, Darwin calculated that “the denudation of the Weald must
haverequired 306,662,400years; orsaythree hundredmillion years.” 5 Almost im-
mediately, critics pounced on what they saw as an absurdly high result. Darwin
began rapidly to backpedal from what he came to call “those confounded millions
of years.” 6
No Further Funds at Our Disposal
T. Mellard Reade (1832-1909), a British architect, engineer, and amateur geolo-
gist, was another hourglass calculator. Phillips and others had used the amount of
sediment carried by the world's great rivers, but Reade thought he had a better
method: the amount of “soluble constituents”—dissolved salts like carbonates,
sulfates, and chlorides—in river water. 7 Using the rate of delivery of salt to the
ocean and the amount of salt in the ocean, Reade had a new hourglass.
Reade improved on some of Phillip's assumptions but made at least as many
himself. After “laborious” calculations, his answer for the age of the sedimentary
rocks came out at 526 million years, which he regarded as a minimum. 8 Paraphras-
ing Hutton, Reade concluded, “We may speculate on a beginning, but we can find
no trace of it by geological methods” (30).
Although Reade had said that “it defies calculation to reach a maximum beyond
which we can say the age of the earth does not extend,” in 1893, he defied himself
by making just such a calculation (27). “Physicists say that from the thermal con-