Final answer:
Alfred Wegener's theory of continental drift was rejected because he couldn't provide a mechanism for how continents moved. His idea was too radical for the era's scientific consensus. Later, the theory of plate tectonics provided the needed evidence and mechanism, validating Wegener's hypothesis.
Step-by-step explanation:
When Alfred Wegener proposed his theory of continental drift, the scientific community rejected his ideas primarily because he lacked a plausible mechanism to explain how the continents moved. Wegener's hypothesis, introduced in 1915, suggested that the continents were once joined in a supercontinent called Pangaea and had since drifted apart. He presented evidence such as the jigsaw fit of continents, similar fossils found on different continents, and matching geological formations, which pointed towards previously connected landmasses. However, the concept of solid continents moving thousands of miles was, at the time, considered revolutionary and went against prevailing scientific understanding.
Moreover, the geological data available in the early 20th century was insufficient to support such a dramatic rethinking of Earth's structure. The development of the theory of plate tectonics several decades later provided the needed mechanism and evidence, validating Wegener's initial ideas and revolutionizing the field of geology. At that point, the once-controversial concept of continental drift became widely accepted and formed the foundation for our modern understanding of a dynamic Earth.