Geology Reference
In-Depth Information
3
Why moving plates?
How were plates conceived of? How do we know they move? How were
mantle plumes conceived?
The main story of the idea of continental drift and its ultimate transformation
into the theory of plate tectonics has been well told (e.g. [12, 13]), and will not
be recounted in detail here. However, the particular observations that led to the
conception of moving plates are perhaps not so well known, as evidenced by
the lack of recognition of the person who first conceived of plates. Also, the
evidence that persuaded large segments of the geophysical and broader geological
community of the reality of moving plates is worth repeating, so we know we
are dealing with a theory well based in observations, and not just accepted on the
authority of textbooks already a few decades old. (I say 'already' because I came
into the Earth sciences in 1968, just after the view of the geophysical community
had been transformed, and before many geologists had been persuaded, so of course
to me it doesn't seem long ago.)
3.1 The lead-up
Alfred Wegener conceived of continental drift around 1912 [14] on the basis of the
rough match of continental outlines across the Atlantic Ocean, which he was not
the first to notice. He supported the concept with geological and palaeontological
evidence. He refuted with sound physics the rival theory of land bridges that
had risen and sunk, notably that there should be large and observable gravity
anomalies associated with such changes. His arguments were opposed by people,
notably Harold Jeffreys [15], who had little knowledge of the relevant properties of
solids, and in particular apparently little awareness of good geological arguments
13
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