An Idea to Pursue - Four Revolutions in the Earth Sciences - page 53

quakes and floods.” 3 Several others, including the Prussian explorer and natural-
ist Alexander von Humboldt and the French geographer Antonio Snider-Pelligrini,
would also note the similarity of the facing Atlantic coastlines. But it was Alfred
Wegener who fully developed the idea.
Wegener's private letters showed that by 1911 he had grasped what many geo-
logists found hard to swallow: The old ideas were fading, but there were no satis-
factory new ideas to replace them.
During the second half of the nineteenth century, scientists accepted LaPlace's
modelfortheoriginofthesolarsystem,whichenvisionedtheEarthasbornmolten
and having been cooling and contracting ever since. This led the American geo-
logist James Dwight Dana (1813-1895) to develop a model in which contraction
provided the force for geologic change. Dana thought the portions of the Earth that
cooled first had become the continents, followed by the slower cooling and further
contraction of portions that became the ocean basins. According to this view, the
continents and ocean basins have been present since near the beginning of geolo-
gic time: they are permanent.
The Austrian geologist Eduard Suess (1831-1914) more fully developed the
contraction idea in a multivolume work called Der Antlitz der Erde ( The Face of
the Earth ). 4 As contraction continued throughout earth history, Suess wrote, sec-
tions of the continents that had foundered to become ocean basins were uplifted
again to reappear as continents, while adjacent sections themselves foundered to
become new ocean basins, and so on. Continents and ocean basins are thus inter-
changeable, differing onlyinelevation. Suessbelieved that contraction hadcreated
the Earth's mountains as the rigid outer crust compressed to fit around the shrink-
ing interior, like the skin of an apple wrinkling as the core desiccates beneath it. 5
“The breaking up of the terrestrial globe, this it is we witnessed,” Suess wrote.
“Great segments of the Earth's crust have sunk hundreds, in some cases even thou-
sands, of feet deep, and not the slightest inequality of the surface remains to indic-
ate the fracture. Time has leveled all.” 6
By the twentieth century, the weaknesses in Suess's model had become all too
obvious. Why are the wrinkles on the apple skin—the mountain belts—restricted
to a few elongate regions of the Earth rather than spreading more evenly across
the globe? If contraction goes on continuously, why has mountain building pro-
ceeded in waves, each followed by quiet periods? Why did the Alps, the Andes,
the Himalayas, and the Rockies rise during the Tertiary period, after most of geo-
logic time had already passed? Why do the world's large mountain ranges differ
so? 7 Such questions cast doubt on contraction, but three new findings sank it. They