Geoscience Reference
In-Depth Information
er turned to the work of the Swiss geologist Émile Argand, who had shown that
when the Southern Hemisphere continents are reassembled, folding and other geo-
logical features align. This led Argand to become one of drift's strongest support-
ers, writing that “the soundness of any theory is no more than its ability to portray
the entirety of facts known to date. In this respect the theory of drift of the large
continental land masses is in an excellent state of health” (96).
Then came the arguments from paleontology and biology. Here much of the
evidence had been assembled by generations of paleontologists, though in Wegen-
er's view they had misinterpreted that evidence to support the idea of land bridges.
Infuriatingly to Wegener, some did not even seem to care: “A large proportion of
today's biologists believe that it is immaterial whether one assumes sunken contin-
ental bridges or drift of continents—a perfectly preposterous attitude” (97).
The fossil evidence for drift, he wrote, “is particularly clear in the case of the
former land connection between South America and Africa.” He cited two ex-
amples. First were fossils of a small Permian reptile,
Mesosaurus
, found only in
southeastern Brazil and southwestern Africa, and in identical rocks. Second was
the fossil fern
Glossopteris
, found in all the Southern Hemisphere continents. How
could these organisms, and countless others, have crossed thousands of miles of
ocean water? They couldn't: there must have been some land connection between
the continents. It came down “simply to a matter of choosing between drift theory
andpermanenceoftheoceanbasins”(98).Butgeologistshadalreadyfalsifiedper-
manence.
From ancient organisms Wegener turned to living ones. How, for example, ex-
cept by drift can one explain the remarkable similarity of modern earthworm gen-
era on different continents? An author who had reassembled the continents using
species of a single earthworm family found that continental drift explained the dis-
tribution “in quite a remarkable way” (116). Or take the peculiar Australian mar-
supials and monotremes, like the platypus, that have no close relatives in the rest
of Asia but whose South American cousins closely resemble them, down to their
parasites. How other than by continental drift to explain that of 175 species of a
singleflatwormfamily,three-quartersarefoundonlyinAustraliaandSouthAmer-
ica (109)?
Wegener was neither a geologist nor a paleontologist; in those fields he had to
rely on the work of others. But in paleoclimatology he was an expert. Certain rock
types reveal the climate that existed when the rocks were deposited. Glacial tillites
connote cold conditions; coal, high humidity; desert sandstones, aridity; salt and
gypsum, warmth and evaporation; thick limestone beds, warm waters of the trop-
ics and subtropics; and so on. Fossil plants and animals also provide clues: the ab-
