One of the original evidences, also for sea floor spreading, was magnetic mapping in the Atlantic during WWII for ASW purposes.
If your wandering around in the middle of nowhere and find magmatic outcrop with neat little holes cored in it, its from “paleomaggots”, guys that study/survey the magnetic record frozen in the rock at cooling.
Next time I’m out hiking the bottom of the Atlantic, I’ll keep an eye out for those holes.