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good deal of creativity, filled in the many gaps in data with the kind of
patterns that she divined
should
be there. Her powers of inference were
considerable. From the early data, back in the early 1950s, she began
to suspect that the top of the Mid-Atlantic Ridge was not, in fact, a
ridge. Rather, running right down the middle of this enormous ele-
vated mass there was a notch: a narrow valley, that she thought resem-
bled a rift valley, where a long central plug of rock had slid downwards
between two parallel fault planes. 'Nonsense,' snorted Heezen, 'that's
just girl talk.' Marie Tharp stuck to her guns—and she was right. She
had discovered one of the fundamental structures in the ocean (Fig. 5).
It showed that the ridge was not so much being pushed up as pulled
apart (and Heezen was later to give her credit for being right). It's a
pity, though, that the realization was to lead them both, for a time, up
a very bizarre garden path.
The Ocean Machine
One of the reasons why Bruce Heezen didn't at first like the idea of a
rift valley running the length of the Atlantic was because, like many
geologists of the 1950s, he thought that continental drift was non-
sense. Yes, the edges of the continents did seem to fit together in an
uncanny sort of way, as Alfred Wegener and others had suggested
years ago. And yes, the crust of the oceans was different, being denser
(because of having more iron and magnesium and less silica) than
that of the continents. This explains why the continents are raised
high, and why the ocean floor lies several kilometres below them. But
to plough the continents for thousands of kilometres
sideways
through
the oceans? That was absurd, surely.
However, when Heezen convinced himself of the rift valley in the
central Atlantic, and saw that the whole ocean must be pulling apart
along the rift, with basalt lava welling up to fill this ever-opening frac-
ture, he agreed that the oceans must be getting bigger. This needed
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