Due to the theory of continental drift, continents and landmasses can move apart and together on plates. This particular case has the fossils dating back to approx. 300 mya, when there was the supercontinent Pangea. During this time, all modern continents were squished together, allowing for all of the continents mentioned in the question above to be connected, in turn allowing for the Glossopteris plant to grow and fossilize on all of the continents.
