His criterion could only have been that they seemed compelling to him. His guyots, he had by now decided, were volcanoes that grew at spreading centers, where they protruded above the ocean surface and were attacked by waves. With the moving ocean floor they travelled slowly down to the abyssal plains and went on eventually to “ride down into the jaw crusher” of the deep trenches, where they were consumed. “The earth is a dynamic body with its surface constantly changing,” he wrote, and he agreed with others that the force driving it all must be heat from deep in the mantle, moving in huge revolving cells (an idea that had been around in one flexplek huren groningen form or another since i839 and is still the prevailing guess in answer to the unresolved question: What is the engine of plate tectonics?). Hess reasoned also that the heat involved in the making of new seafloor is what keeps the ocean rises high, and that moving outward the new material gradually cools and subsides. The rises seemed to be impermanent features, the seafloor altogether “ephemeral.” “The whole ocean is virtually swept clean (replaced by new mantle material) every three hundred to four hundred million years,” he wrote, not then suspecting that ocean crust is actually consumed in half that time. “This accounts for the relatively thin veneer of sediments on the ocean floor, the relatively small number of volcanic seamounts, and the present absence of evidence of rocks older than Cretaceous in the flexplek huren amsterdam oceans.” In ending, he said, “The writer has attempted to invent an evolution for ocean basins. It is hardly likely that all of the numerous assumptions made are correct. Nevertheless it appears to be a useful framework for testing various and sundry groups of hypotheses relating to the oceans. It is hoped that the framework with necessary patching and repair may eventually form the basis for a new and sounder structure.” In i963, Drummond Matthews and Fred Vine, of Cambridge University, published an extraordinary piece of science that gave to Hess’s structure much added strength. Magnetometers dragged back and forth across the seas had recorded magnetism of two quite different intensities. Plotted on a map, these magnetic differences ran in stripes that were parallel to the mid-ocean ridges.