In science class, they teach us about tectonic plates. That I can comprehend. Plates just under the earth's surface that float above an inner layer of magma. That I understand. But what I don't understand is that if the plates move, and are continually being recycled in the Earth's core thanks to the rock cycle, how do we know how old the earth is according to evolution? Because if the tectonic plates really do fold under each other to the point where they are melted, renewed, then return to cooler areas where they rejoin the tectonic plates only to do the whole circuit again, how can we use the earth to tell how old it is? Have I made a point that someone can explain to me, or is my education really bad?