Geoscience Reference
In-Depth Information
No Way
Let us now return to Fred Vine, at Cambridge in January 1962, listening to Harry
Hess. The talk so inspired young Vine that he titled his own forthcoming student
address to the Cambridge Geology Club “HypotHESSes.” In the early 1960s, it
was a rare geologist who knew and accepted both that the Earth's magnetic field
had reversed and that the seafloors were spreading from the ridges. Hess's ideas
had reached the broader geological community only with the Buddington volume
in November 1962, and such a specialized topic typically is not widely read. Being
able to hear directly from Hess early that year, Fred Vine was in the right place at
the right time. But that was not enough. A scientific breakthrough requires a mind
prepared to think the previously unthinkable.
Vine set to work interpreting Matthews's magnetic data from the Carlsberg
Ridge, focusing on two puzzling underwater volcanic seamounts. He found he
could interpret their magnetism by assuming that one was normally magnetized
and the other reversed, as though the lava forming one seamount had solidified
while the magnetic field was normally oriented and the other while the field was
reversed. Extending this thought to what to anyone else would have seemed an ab-
surdity, Vine wondered whether half the entire seafloor could be normally magnet-
ized and the other half reversed. That could have happened if submarine volcanic
eruptions had occurred randomly through time, and over the entire seafloor, some
erupting when the field is normal and some when it is reversed. But if Hess were
right about seafloor spreading, there was another way: volcanic rocks could erupt
on the ridge crest above an upwelling convection cell, solidify, magnetize accord-
ing to the polarity of the magnetic field at the time, and be swept to either side. By
the time the next batch of lava erupted, the field might have reversed. Then strips
of alternating polarity would lie in long, linear bands of positively and reversely
magnetized rock parallel to the ridge crest and reveal themselves as the stripes on
the Raff-Mason map. Vine said that “although in a way [this insight] was a big
leap, for me it was a fairly small leap,” both because he “believed in spreading”
and because it instantly made sense of otherwise “very improbable structures”: the
zebra stripes.
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