21.   The composition of displaced terranes ranges from that of typical oceanic crust to significantly less dense granitic rock with clear continental affinities.

22.   As these plateaus are more buoyant than normal oceanic crust they would tend to resist subduction and therefore be accreted to continents lying along plate margins.

23.   As the oceanic crust dives into trenches, the continental crust collects above them.

24.   As the oceanic crust moves deep into the mantle, it takes water with it, embedded in the molecules of the rock.

25.   Continental crust is on average five times thicker than oceanic crust, and it tends to be far more ancient.

26.   Subducting oceanic crust can also act like sandpaper, tearing off bits of overlying continental crust as it sinks.

27.   That, anyway, is classical plate tectonic theory, and it works fine for oceanic crust.

28.   The idea is reinforced by seismic analysis indicating the object reflects seismic waves in a more complicated manner than ordinary oceanic crust.