CompuServe Thread

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