The direction of the poles shows in rock strata. As magma cools, anything magnetic will line up and show the direction.
Sea floor spreading leaves the same telltale . . . magma upwelling and being cooled by the ocean takes on the magnetic polarization at the time it solidifies. Alternating stripes of different magnetic polarization document the pole flips and constituted validation of the spreading theory.Back in the 1950s you could sit in a classroom with a map of the world up front, and see plain as day that the continents looked like fitting jigsaw pieces - and yet be told when you questioned it, that that was not significant. Finally they did paleo research and found that ancient rocks from different sides of the ocean matched up. And then there was the magnetic pole reversal mapping on the sea floor . . .