Rocky III


March 1, 2008

When it comes to plate tectonics, dinosaurs help tell the story.

The recent Carved in Stone articles have talked about  Rocky — a 1.8-billion-year-old grey and pink banded metamorphic  rock referred to as “gneiss” (pronounced nice). Last month, we saw how Rocky wandered around the globe and learned how the  magnetic minerals in the rock  help geologists determine the  path he took. I also lamented  that my grand kids Donovan  (4 years old) and Delaney  (3 years old) probably do  not care much for magnetic  minerals or plate tectonics. Well, there  is more to the story. Here is something I  am sure the kids will like — dinosaurs!

Between 248-206 million years ago,  South America, Africa, Antarctica,  India, and Australia were all clumped  together. As early as 1596, Dutch map  maker Abraham Ortelius suggested that  the Americas were “torn away from  Europe and Africa” and that “the vestiges  of the rupture reveal themselves,  if someone brings forward a map of the  world and considers carefully the coasts  of the three [continents].” Ortelius’ idea  resurfaced in 1858 when geographer  Antonio Snider-Pellegrini made a map  showing how the American and African  continents may have fit together.

However, it was not until 1912 that  the movement of continents was given  serious consideration as a scientific theory.  Alfred Wegener, a German meteorologist,  proposed that the land masses  on the globe had been a single continent  and that they began to break apart  about 200 million years ago. His theory  was based, in part, on the remarkable  fit of the South American and African  continents. But Wegener  was intrigued by the occurrence  of unusual geologic  structures and fossils found  on matching coastlines of  a number of continents (as  shown on the accompanying  illustration), which are  now widely separated by  oceans. Cynognathus and  Lystrosaurus were land reptiles.  If they tried to swim  across the ocean they would  have sunk like a rock. Mesosaurus  was a freshwater  reptile and couldn’t swim  very far, certainly not  across the ocean. Glossopteris  — it was a fern with big heavy seeds that could not be blown across  the ocean. Wegener reasoned it was  impossible for these organisms to  traverse the great distances across the  oceans. To him, the fossils were the most compelling evidence that the  continents had once been joined.

Scientists have used this evidence  to help develop the theory of plate  tectonics and reconstruct Rocky’s  journey across the globe. The next time Donovan or Delaney wear their dinosaur pajamas, I will tell them the  story of Cynognathus, Lystrosaurus,  and Mesosaurus.

Do you think they will like it?

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