At http://phys.org/print400858229.html …. apparently, ocean bottom crust in the modern world is thinner than it was prior to the break up of the supercontinent of Pangea. Plate tectonics has subsequently caused the crust to cool and at the same time thin it. All that heat and plate activity after 170 million years ago is being blamed for a thicker ocean floor crust at that time. The study involves computer modelling.
Meanwhile, at http://phys.org/print400958143.html … a new study into Plate Tectonics that involves understanding what comes up and what goes down into the Mantle. This is where the olivine rock comes in as olivine is supposed to be a marker of former Mantle material.