Final answer:
The distribution of Glossopteris fossils supports continental drift as it suggests these plants once existed on a connected supercontinent, with evidence too compelling for coincidence, seed density, absence of bird dispersal, and ancient climate differences.
Step-by-step explanation:
The distribution of fossils of Glossopteris on landmasses that are widely separated today was cited as evidence for continental drift primarily for several reasons. First, the existence of identical life forms on landmasses that are now vast distances apart could not be easily explained by coincidence alone. Also, the seeds of Glossopteris were likely too dense to float across such significant expanses of ocean, ruling out natural seed dispersal through water. During the time that Glossopteris thrived, birds were not yet present to assist in the spread of its seeds across oceans. Additionally, fossils of this plant are found in Antarctica, which is currently much too cold to support the lush plant life that once existed.
Alfred Wegener's theory of continental drift was initially conceived upon observing the congruent shapes of continents, and it was bolstered by fossil evidence showing similar species on widely separated continents. This was the case with Glossopteris, indicating that the continents of Africa, South America, Australia, India, and Antarctica were once connected, forming part of a supercontinent named Pangaea. Wegener's evidence suggested that these continents harbored the same flora at one time, supporting the idea that they were once joined and have since drifted apart due to tectonic plate movement.
Biogeography today helps explain the distribution of organisms based on evolutionary changes in conjunction with the movement of tectonic plates over geological time. Broad groups of organisms, like Glossopteris, that evolved before Pangaea broke up are found worldwide, indicating their distribution before the continental separation.