It is fairly common in thinking about the Earth to find that variation or progression through space is closely connected with variation or progression through time. For example, within a basin of undeformed sedimentary rocks, the downward direction corresponds to increasing time since deposition. On the seafloor, distance away from the mid-ocean-ridge spreading center corresponds to increasing time since formation of that strip of seafloor. As a consequence, geologists often think about distance in space when they really want to be thinking abo
