Final answer:
Alfred Wegener proposed the continental drift hypothesis but was considered an outsider because his idea lacked sufficient evidence and a plausible mechanism for the movement of continents. His theory was eventually accepted as evidence for plate tectonics accumulated.
Step-by-step explanation:
Alfred Wegener was indeed considered an outsider by the scientific community primarily because of his revolutionary idea, which was the continental drift hypothesis. Born in 1880 in Berlin, Wegener was passionate about the Earth sciences and eventually proposed the idea that the continents are slowly shifting. Despite his formal education and doctorate in astronomy, his transition to Earth sciences and lack of a comprehensive mechanism to explain the movement of continents led to skepticism from his peers. His theory did not gain acceptance until much later when more evidence emerged and supported the concept, which then became central to the modern understanding of a dynamic Earth.
Wegener's hypothesis faced resistance due to the scientific community's requirement for more evidence and a clear mechanism that would fit with the existing understanding of Earth's processes. However, after Wegener's death, and with the advancement of scientific research, his ideas were eventually vindicated, leading to the widely accepted theory of plate tectonics.