Hello :) So the continental drift theory is basically saying that the continents were once attached in a big mass of land and drifted apart over time. The depth of the oceans don't really have anything to do with this. Neither does the climate in South America or the size of glaciers. Fossils of the same kind however, were found in several continents. This supports the theory that animals once roamed around in that area when the continents were attached. Hope this helps. :D