Now we know that heat causes movements of the mantle, mainly the upper mantle, within the interior of the earth. Let's return to the surface at the mid-ocean ridges, which we identified in our transect across the Atlantic.
During and after World War
II, oceanographers used echo profilers to measure the water depths and
identify some of the features on the seafloor.
Remember echo-profiling, or
echo-sounding, is where sound is sent out from the
bottom of a ship and an echo is returned from the seafloor. The
resulting profiles of the seafloor, although few in number, were used to
make the first modern maps of the seafloor
around the world.