#Continents in Collision
For all who have been lurking on the recent threads about continental drift and
plate tectonics, and would like to know more about the subject, I'd like to
recommend a book I found at Half Price Books yesterday, called CONTINENTS IN
COLLISION. It's one of Time-Life Books' series about Planet Earth. While I
generally don't think much of Time-Life publications, this series is an
exception. The photography and artwork are excellent, and the text is well
written and easy to follow.
The book starts by looking at the old geological orthodoxy, the
contracting-earth theory, then reviews various ideas of continental motion
advanced in the 1800s and early 1900s. All of them foundered on one simple
thing: they couldn't provide a mechanism. It wasn't until after WW II, with
the development of new and sophisticated methods of probing the ocean floors,
that the required mechanism was found in the form of sea-floor spreading,
transforming the hypotheses of continental drift into the comprehensive theory
of plate tectonics.
Despite the fact that it's written for a nonscientist, and suffers a bit from
oversimplifying things, this is really an excellent look at modern geology.
The idea that a picture is worth a thousand words is proven true by a spread on
pp.84-5, a reproduction of sub-bottom sonar scans of the Kuriles Trench north
of Japan, the meeting place of the Pacific Plate and the Eurasian Plate, where
the Pacific Plate is being subducted. The scans are detailed enough to show
multiple layers of sediment as well as the bedrock layer below. The scan
plainly shows both plates curving sharply downward, but the Eurasian Plate
simply stops where it meets the Pacific Plate, while the Pacific Plate is
clearly visible continuing even deeper. Better proof of subduction one could
not ask for.
What's most impressive about the history of continental-motion ideas is two
things. First is how very fast orthodox geology reversed itself in the 60s and
embraced the idea when only ten years before it was considered purest nonsense.
Since established scientists tend to be a conservative bunch, this can be taken
as proof of how convincing the new theory was, and how inadequate the old ideas
all were.
Second is how sea-floor spreading and then plate tectonics proved to be a grand
unifying theory of geology. _Everything_ came together under plate tectonics:
volcanology, seismology, terrestrial geology, oceanic geology, it all came
together into one coherent whole. In twenty years it completely swept away all
possible counter-theories, explaining every known fact and incorporating every
new discovery without faltering. A faster, more complete scientific revolution
I've never heard of.
JSW