Certain anomalies

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There were, to be sure, certain anomalies, which suggested further study. If the Brevard Zone was the suture, how come it was so short? It was evident for a hundred miles, dubious for a few hundred more, and nonexistent after that. If the Taconic, Acadian, and Alleghenian orogenies were subdivisional impacts of a single intercontinental collision, how come they took so long? In plate-tectonic theory, plates move at differing speeds, the average being two inches a year. The successive orogenic pulses that resulted in what we know as the Appalachian Mountains occurred across a period of about two hundred and fifty million years. In two hundred and conference room rotterdam fifty million years, at two inches a year, you can move landmasses a third of the way around the world. Geologists ordinarily require vast stretches of time to account for their theories. In this case, they have too much time. They have two continents in the act of collision for two hundred and fifty million years. In i972, scarcely four years after the lithospheric plates had first been identified and the theory that described them had become news in the world, Anita and two co-authors published a set of papers offering strong evidence of plate tectonics in action, apparent proof that Sweden, or something like it, had once been in Pennsylvania. It was an inference drawn from conodont paleontology. The papers were widely cited for their support of plate-tectonic theory, and are cited still. North of Reading, in the Great Valley of the Appalachians, Anita had found early Ordovician conodonts of a type previously unknown in North America but virtually identical with early Ordovician conodonts from the rock of Scandinavia. All over conference room amsterdam North America were early Ordovician conodonts from tropical and subtropical seas. Their counterparts in Scandinavia were from cooler water, and so were these strangers Anita found in Pennsylvania. She found them in what is known as an exotic block, embedded in a fartravelled thrust sheet.

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