The older students should be able to complete the puzzle in a shorter amount of time than the younger students
The shape of the continents had been observed, that they fit together like a puzzle; this is easy to see with Africa and South America. Volcanoes and earthquakes had been found to only erupt in certain places - at the plate boundaries. Also, similar fossils had been found where the continents may have been connected. When satellite was introduced, some plate boundaries could even be seen from outer space.
forward reaction equals reverse reaction