Final Answer:
Wegener believed continents were once joined based on matching coastlines (e.g., South America and Africa) and shared geological features and fossils. His theory, later supported by plate tectonics, explained past continental drift.
Step-by-step explanation:
Alfred Wegener proposed the theory of continental drift in the early 20th century, suggesting that continents were once part of a supercontinent called Pangaea. His primary observation was the apparent fit of the coastlines of South America and Africa, which led him to speculate that these continents were once connected.
Wegener also noted similarities in geological features, such as identical rock formations and the presence of identical fossils on continents now separated by oceans.
Despite Wegener's compelling evidence, his theory faced skepticism during his time due to the lack of a mechanism explaining how continents could move. It wasn't until later, with the development of the theory of plate tectonics, that Wegener's ideas gained widespread acceptance. Plate tectonics provided the mechanism for the movement of continents and offered a comprehensive explanation for various geological phenomena.