Continental Drift: Not Even Wrong - Four Revolutions in the Earth Sciences - page 81

A rising and diverging convection cell, shown by the arrows, pulls a continental
block apart and drags the sundered fragments, now continents in their own right,
to either side. In between, a new ocean basin forms. Since the lighter continental
material cannot sink into the denser mantle, it piles up at the edges, where “moun-
tain building would have been accomplished on the continental margins.”
If oceans can open as Holmes illustrated, can they also close? How else could
the putative supercontinent, Pangaea, have assembled but by continental drift in
reverse? Holmes noted that Van der Gracht had suggested that the Atlantic Ocean
mighthavehadanancestor thatclosed duringtheeventthatcreated theAppalachi-
ans and the Caledonides. “Granted convection currents,” Holmes wrote, “the con-
tinents may open out and reclose in an endless variety of patterns” (346). Here
Holmes was forty years ahead of his time.
Holmes took Wegener's theory, with its many flaws but generally correct
concept, and improved it to the degree possible in the late 1920s. Certainly, he got
some details wrong. But four decades after Holmes's 1929 paper, geologists ac-
cepted convection as the mechanism of drift. We accept convection today, even
though we still do not fully understand how it works.
Fairytale
In the last sentence of his TGSG article, Holmes wrote that the “general geological
success [of the convection-current model] seems to justify its tentative adoption as
a working hypothesis of unusual promise.” 12 But as we have seen, geologists ig-
nored this appeal to their oft-avowed principle.
In December 1930, Schuchert read Holmes's 1929 TGSG article. It sufficiently
impressed him that he wrote to another Yale colleague, Chester Longwell, saying,
“It is along the lines laid down by Holmes that geologists will eventually solve the
causes of reformative mountains and how they are made.” 13 Schuchert's wish to
use the downturning convection cells to get rid of land bridges when they were
no longer needed might explain his enthusiasm. But Holmes had firmly and re-
peatedly rejected the sinking of land bridges, much less entire continents. At about
this time, Schuchert began to fall sway to Willis, who admonished the apparently
vacillating paleontologist, “Pray don't get Wegener and Willis mixed up in your
mind.” 14 Schuchert never again did.
Theyear1932sawthepublication ofthetwinpapersfromSchuchertandWillis:
“Gondwana Land Bridges” and “Isthmian Links.” A new generation would show
that land bridges and isthmian links had been figments of the imagination, yet the