What evidence did Alfred Wegener use to support his hypothesis of continental drift? What additional evidence was added later (post-World War II) that suggested seafloor spreading? How do these two ideas unite to form the theory of plate tectonics?

Question

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Answer 1

Answer: Wegener noted (a) the shape of the continents, (b) paleoclimatic evidence including glaciation of the southern portion of the Pangean supercontinent, (c) terrestrial fossil organisms that matched up across ocean basins, and mountain belts such as the Appalachians/Caledonians. After World War II, the shape of the seafloor was revealed, and it included both oceanic ridges and deep-ocean trenches. These observations gave rise to the idea of seafloor spreading. Paleomagnetic signatures in the oceanic crust, the thickness of seafloor strata (found out via oceanic drilling) and hot-spot tracks (from mantle plumes) helped to reinforce the idea of plate tectonics. The basic idea behind plate tectonics is that the lithosphere is broken into a series of slab-shaped fragments called plates, and these plates move due to the motions of the underlying mantle. They can move together, producing convergent boundaries (deep-ocean trenches, volcanic island arcs, continental volcanic arcs, or mountain ranges form at the boundary); they can move apart (continental rifts and oceanic ridges form at the boundary); or they can slide laterally past their neighbors (earthquakes and offset features will occur at the boundary).