Geoscience Reference
In-Depth Information
sence of annual rings in fossil trees, for example, indicates a tropical climate; the
presence of Glossopteris , a wet one.
Geologists had long known that the climate of Europe had varied considerably
inthe past. Some ofthe most convincing evidence fordrift came fromSpitsbergen,
the largest and only inhabited island in the Svalbard archipelago midway between
Norway and the North Pole. At 78°45' North, Spitsbergen faces the chilly Arctic
Ocean, but its rocks and fossils reveal that its climate had once been more clement.
During the lower Tertiary, this now frigid spot had magnolia, grapevines, and a
wider variety of trees than central Europe has today. Going back farther in time to
the Carboniferous, the island had sago palms, now found only in the tropics. Still
farther back and beds of gypsum reveal that Spitsbergen once had a dry, subtropic-
al climate.
The late Paleozoic glacial deposits capped the evidence for drift. Geologists had
found them not only in South Africa but in each of the Southern Hemisphere con-
tinents and even in the Falkland Islands off the tip of South America. As Wegen-
er noted, these traces of a late Paleozoic ice age “are now widely separated and
involve almost half the surface of the globe!” 12 At the time that Spitsbergen was
warm and sunny, an inland ice sheet buried South Africa. Thus one could not ex-
plain the climate of one or the other location by claiming that the entire globe
had warmed or cooled. Continental drift, on the other hand, could easily resolve
the conundrum: merely assume that the Southern Hemisphere continents had once
clustered around the South Pole. “No better corroboration of our theory could be
desired,” Wegener summed up. 13
There was one just one problem: in a few places, late Paleozoic rocks that geo-
logists had classified as glacial tillites did occur in the Northern Hemisphere, well
outsidetheGondwanalandclusterandwhere,accordingtodrifttheory,theyshould
not have been. The best known of these was the Squantum Tillite, a well-studied
rock formation near Boston. Wegener argued that his theory should be judged “by
the large number of reliable and mutually consistent pieces of evidence, not by the
one anomaly” (136). By this time he had taught himself enough geology to know
that jumbled glacial deposits can be hard to distinguish from landslide and mud-
flow debris. He speculated that the Squantum Tillite would turn out to be “pseudo-
glacial, as so many other conglomerates already have” (136). He turned out to be
right. But for his many critics, one exception disproved the rule. 14
Wegener could not suppress his frustration: “The obvious needs no backing by
outside opinion, and the willfully blind cannot be helped by any means,” he wrote.
“As far as we are concerned, it is not now a question of whether the continental
blocks have moved; doubt is no longer possible” (133).
Search WWH ::




Custom Search