Geoscience Reference
In-Depth Information
The Newton of Drift
Wegener saved the mechanism of drift—the “displacement forces”—to near the
end of the topic. He noted that to this point he had proceeded empirically, “without
making any assumptions about the origin of the processes.” This, he wrote, is the
proper method of science. Only after “the formulation of the laws of falling bodies
and of the planetary orbits was first determined purely inductively . . . did Newton
appear and show how to derive these laws deductively from the one formula of
universal gravitation.” Wegener added, “the Newton of drift theory has not yet ap-
peared. His absence need cause no anxiety; the theory is still young and still often
treated with suspicion. It is probable, at any rate, that the complete solution of the
problem of the driving forces will still be a long time coming” (167).
Having the advantage of hindsight, one can argue that that would have been
an excellent place for Wegener to write “The End” and begin planning his next
expedition. But he did not, instead going on to search in vain for the cause of
drift, thereby providing his critics with the one argument that they would use most
tellingly against him and his theory: drift “lacked a mechanism.”
In his discussion of possible causes, Wegener began with the Hungarian phys-
icist Baron Roland von Eötvös, who had studied the gradient of gravity on the
Earth's surface. Owing to the Earth's shape as an oblate spheroid, Eötvös said, a
small force, the
polflucht
, would propel continents toward the equator. Wegener
identified the Eötvös force “as the only one of which we have precise knowledge”
(168) and argued that the “pole-flight force is enough to displace the continental
blocks through the sima [the fluid substratum], but not enough to produce the great
fold-mountain ranges” (174). The latter fact did not concern Wegener, who wisely
argued in effect that since fold-mountains exist, so must the forces that produced
them, even though we may not be able to identify those forces (174). This would
have been the ideal argument to extend to the entire planet.
From there Wegener moved to other possible causes of drift, such as the tides
pulled in the solid Earth by the attraction of the Sun and the Moon, the precession
of the equinoxes, and so on, a limp and unpersuasive list little advanced from the
putative causes identified in his 1912 paper (175).
On the next-to-last page of the main section of the topic, Wegener came up with
a provocative idea that he attributed to others: “convection currents in the sima.”
Thanks to the heat from radioactivity, he wrote, the warming sima might “rise be-
low the continents up to their lower boundary, then flow along under them to the
ocean region, where it turns downwards, returning to the continents after reach-
ing greater depths.” The resulting friction could “disrupt the continental cover and
