Travel Reference
In-Depth Information
did a given mountain chain form, or an ancient sea? When did a particularly
interesting or important evolutionary event occur? The tools we need to
take these first steps in reconstructing the past vary from the simplicity of a
rock hammer to the arcane electronics of an atom-separating mass spectro-
graph.
How do you tell time in the present? You look at your watch or the
clock on the wall. And if no clock was available? You listen to the radio or
watch television and wait for some announcement of the time. But say these
avenues are cut off as well. Now you must rely on far more basic and crude
time keepers: sunrise and sunset. Perhaps you can estimate high noon. But
the middle of the night on a cloudy evening? Remove technology, and time
becomes a very different—and difficult—quantity to pin down.
Without technology, time moves from the absolute to the relative—
with no recourse to an external standard, one's ability to determine time be-
comes a relative measure. Day follows night; midday follows morning; a
grumbling stomach follows sleep. Time-keeping in such circumstances is very
crude, just like trying to date a random fossil found on a beach. You have
awakened in the middle of the night, wondering what time it is; you have
found a fossil on the beach, wondering how old it is. Without some contex-
tual information and with no technology available, you are lost. But even
here the metaphor breaks down. In the middle of the night you find your
watch, and the riddle is solved. But with the fossil on the beach, there is no
watch that will ever help you, no machine that will ever pin down this fos-
sil's age in anything other than great crude swaths of million-year, or even
hundred-million-year intervals. No wonder the early geologists wrestled so
determinedly with this problem.
More than any other field of science, geology is inexorably linked to
the concepts of time. The science of geology has been described as the sci-
ence of telling time—establishing dates and sequences of earth events.
Sooner or later any geological investigation moves from process to history,
and thus to events that occurred during the passage of some discrete time in-
terval in the past. To a geologist, measuring time is almost a religion. In no
other field of science has it been necessary to codify a time scale applicable only
