March 1, 2008
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?