We are truly in motion no matter where we stand on the planet. The tectonic plates that compose the crust of the Earth are in motion at a measurable rate. Everything on the crust of the Earth changes its location in relation to the planet. Yes, the plates are moving over the mantle, and we can measure this motion to determine the rate of plate movement by figuring the distances and times involved. For example, if we know the past location of a certain island, then we can measure the distance between the present location of the island and its location millions of years ago to determine the speed of the plate on which the island is located.