Final answer:
The coastlines of South America and Africa led to early theories they had been connected, forming the basis for Alfred Wegener's continental drift theory which included the supercontinent Pangaea and contributed to modern plate tectonics.
Step-by-step explanation:
The shapes of the coastlines of South America and Africa led to early suggestions that they had been joined at one time. German scientist Alfred Wegener proposed the idea of continental drift in 1915, supported by evidence including the congruent shapes of continental coastlines and similarities in fossils and living species across these continents.
Wegener's theory suggested that all continents were once part of a supercontinent called Pangaea. This hypothesis set the groundwork for the modern understanding of plate tectonics, though at the time, Wegener's ideas were not fully accepted due to the lack of an explanation for the mechanism causing continental movement.