Geoscience Reference
In-Depth Information
epochs of paroxysmal and catastrophic action, interposed between
periods of comparative tranquillity?"
2
3
He predicted that the question
"will probably for some time divide the geological world into two
sects, which may perhaps be designated as the Uniformitarians and
the Catastrophists."
2
4
He was both wrong and right. The biblical cata-
strophists of Lyell's day were clearly in the wrong and disappeared
more quickly than Whewell predicted, but they have been replaced
by today's neocatastrophists, the pro-impactors.
In order to understand how the earth works, and how geologists
practice their science, the two types of uniformity have to be disen-
tangled. The constancy of law and process, which Gould has called
methodological uniformitarianism,
describes not how the earth works,
but how geologists ought to work. In common with other scientists,
geologists reject supernatural explanations and employ known, sim-
ple processes before they turn to unknown, complicated ones. For
example, today we can see streams eroding and depositing; it is only
logical to assume that they have been doing so ever since liquid
water appeared on the surface of the earth, and that many sedimen-
tary deposits were formed by stream action.
Of course, this is not only the way that all science ought to work
and does. It is nothing more than common sense, well expressed
by William of Ockham in the fourteenth century: "One should
not assume the existence of more things than are logically neces-
sary." Throughout the history of science up to the space age, mete-
orite impact was simply a vague idea with very little to support it.
Thus to endorse it, based on the knowledge available, was to violate
Ockham's razor, as it has come to be called. But today just the oppo-
site is the case. As we will see, scientists today are logically required
to acknowledge that impact has happened numerous times.
All scientists reason from cases in which they can examine cause
and effect to those in which only effect is evident. This is especially
true in geology, where practically everything took place before we
arrived. But nothing is special about methodological uniformity; it
says only that geology is a science.
The classic example of the success of methodological unifor-
mitarianism was the work of Swiss geologist and naturalist Louis
Agassiz, who noted that modern glaciers high in the Alps could be
seen to gouge rocks from their beds and to carry the dislodged
pieces along, sometimes moving boulders as big as a carriage. When
these glaciers melted back, the rocks over which they had passed
were left polished and grooved; as they receded from their points of
farthest advance, they were seen to leave behind ridges of rock
debris. Agassiz then proceeded to find all of these features and more
