Final answer:
Alfred Wegener was the key person to propose the idea of continental drift, which eventually led to the theory of plate tectonics, further developed in the 1960s with contributions from Harry Hess.
Step-by-step explanation:
The key person in the discovery of plate movement was the German scientist Alfred Wegener. Wegener proposed the groundbreaking idea of continental drift in 1915. He suggested that continents once formed a single supercontinent called Pangea and later drifted apart. Despite presenting four key pieces of evidence: the jigsaw fit of the continents, matching fossils, and mountain ranges across oceans, and paleoclimate indicators, his theory met with skepticism due to the lack of a plausible mechanism explaining the movement of continents. It wasn't until the 1960s that Wegener's theory gained traction, notably with the contribution of oceanographer Harry Hess, whose hypothesis of sea-floor spreading provided the missing mechanism and helped to advance the understanding of plate tectonics. Over time, the combination of geological, oceanographic, and geophysical research finally allowed Wegener's idea to evolve into the widely accepted theory of plate tectonics we recognize today.