Final answer:
Alfred Wegener first developed the theory that eventually became known as plate tectonics by proposing the theory of continental drift.
Step-by-step explanation:
The theory that eventually became known as plate tectonics was first developed by Alfred Wegener. Wegener proposed the theory of continental drift in the early 20th century, suggesting that the Earth's continents were once joined together in a single landmass called Pangaea and gradually drifted apart.
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