Box 1.1
Continental drift
The idea of continental drift, proposed by the German geophysicist Alfred Wegener
(1880–1930), was originally motivated by the observation that fossils of identical
plants and animals are found on opposite sides of the Atlantic. The standard
explanation at that time (1911) postulated that land bridges, now sunken, had once
connected far-flung continents, but this could not explain certain geological features
such as the close fit between the coastlines of Africa and South America, the match
between the Appalachian mountains of eastern North America with the Scottish
Highlands, and the fact that the distinctive rock strata of the Karroo system of South
Africa were identical to those of the Santa Catarina system in Brazil. Using these
arguments and a variety of fossil records, Wegener boldly proposed that all these
observations could be explained by assuming that about 300 million years ago all the
continents themselves had once been massed together in a single super-continent he
called Pangea (from the Greek for ‘‘all the Earth’’) which has since been fractured
into the current geography. Wegener was not the first to suggest this, but he was the
first to present extensive evidence for it.
Though some scientists supported this hypothesis, the reaction from the
geophysical community was almost uniformly hostile, and often exceptionally
harsh and scathing. Part of the problem was that Wegener provided no convincing
mechanism for how the continents might move: he envisioned the continents
plowing through the Earth’s crust driven by tidal and centrifugal forces, but his
opponents noted that these forces are too weak for the task, and that the shape of