Final answer:
The scientific community initially rejected Alfred Wegener's continental drift theory due to the lack of a convincing mechanism for how continents could move, but it was later accepted with the development of plate tectonics.
Step-by-step explanation:
When German scientist Alfred Wegener first proposed his theory of continental drift in 1915, the scientific community rejected his ideas largely because he could not provide a convincing mechanism to explain how the continents could move. Wegener had presented evidence such as the shapes of continents fitting together like puzzle pieces, the presence of matching fossils on widely separated continents, and signs that continents had changed position relative to the poles.
However, without a clear explanation of the forces driving continental movement, his peers found the concept too speculative. It was only after the development of the theory of plate tectonics in the 1960s—which offered a comprehensive mechanism for the movement of Earth's lithospheric plates—that Wegener's idea gained widespread acceptance.