1. Discovery of mid-ocean ridges and trenches, as well as oceanic crustal ages that get progressively older from ridges to trenches.
2. Parallel sets of magnetic data recorded in Fe-rich crust that show magnetic reversals in Earth's polarity and support seafloor spreading.
3. Studies showing that it is more likely that the poles are in a fixed position and the continents are moving, as indicated by the orientation of -bearing minerals in crustal rocks.