Geoscience Reference
In-Depth Information
“determined to reject not only many proposed mechanisms such as convection but
also observations and measurements.”
Jeffreys “denied” the implication of the symmetry of magnetic anomalies and
“sarcastically belittled” the evidence of reversals:
The author actually implies that the hypotheses and models of plate tectonics, continental drift,
and convection can be
proved
to be wrong. In the Earth sciences, and perhaps in every natural
science, the easiest thing we can do is make a
model
and test it against observations. To
prove
that nature behaves in a certain way is much more difficult. But to prove that a complex sys-
tem in nature cannot behave in a certain way is extraordinarily difficult. Perhaps it is altogether
impossible.
10
Nur captures what united Bucher, Ewing, Jeffreys, and MacDonald: they re-
garded continental drift as having long been proven to be impossible. Therefore,
they believed, any evidence to the contrary must be mistaken. In contrast to the
other three, however, Ewing did not go out of his way publicly to deride the new
findings. In this writer's opinion, Ewing was wrong but reasonable; Bucher, Jef-
freys, and MacDonald were wrong and unreasonable.
Lack of a Mechanism
By 1965, few geologists and not even all geophysicists accepted both seafloor
spreading and continental drift. Five years later almost all did. But any scientific
theory is subject to replacement by a better one, should the data demand. Could
plate tectonics turn out to be wrong?
In the 1970s, the United States began to establish a network of satellites to allow
precise determination of geographic locations, at first reserving it for the military,
then later making it available to all. As millions of people are now aware, the GPS
application in their cell phone can track their position to within a few feet while
they are out for a walk.
Scientists soon began to set up GPS stations at critical locations to measure
changes in their geographic position over time. They found that the tectonic plates
and the continents they carry are moving in the same direction and close to the
speed that geophysicists had deduced from magnetic anomalies and plate geo-
metry. Thus that tectonic plates move is no longer a theory but an observational
fact, in real time.
But remember that plate tectonics describes only the motion of plates. Have sci-
entists found the missing “mechanism” of drift? By the mid-1960s, most geolo-
gists had come to accept Holmes's then nearly forty-year-old concept of a convect-
ing mantle. According to this model, a rising, diverging convection cell “pushes”
