Virtually identical

Gerelateerde afbeelding

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 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 co-working space zwolle 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 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. They happened to be within a third of a mile of warm-water American conodonts in rock of about the co-working space arnhem same age which had moved hardly at all. The Scandinavian conodonts had apparently come to Pennsylvania with the closing of the protoAtlantic ocean and been dropped ashore off the leading edge of the arriving plate.

Geef een reactie

Het e-mailadres wordt niet gepubliceerd. Vereiste velden zijn gemarkeerd met *