Longitude required a sea-going clock to determine when, for example, the sun is directly overhead. Oceanic crust is being formed today at mid-ocean ridges. The are no analogous formation regions for continental crust, though there is renewal on a geologic time scale. Make a sketch and use the principle of isostasy to explain your answer.
Oceanic crust is more dense.
If the crust is in isostatic balance over a relatively uniform-density mantle, then the greater thickness of continental crust relative to oceanic crust requires that continental crust be less dense. The distribution of seismic activity over the earth is not uniform. Many of the deepest earthquakes are associated with ocean trenches where oceanic crust subducts under continental crust. Shadow zones for S-waves generated by earthquakes, which can't travel through liquids. Whereas P-waves, which can travel through liquids, don't have shadow zones.