Seismologists indicate that the average thickness of basaltic ocean crust is about 7 km. As a thought experiment, imagine that a particular bit of solid oceanic crust with the same bulk density that you calculated for basalt is floating in a sea of upper mantle material that has a bulk density of 3.3 g/cm3 and that is hot enough to flow. (In fact, most of the oceanic crust is on top of a relatively cool, solid part of the upper mantle that does not flow, but let’s not spoil the fun with details.) Use what you have learned about Archimedes’ Principle, buoyancy, and isostasy to estimate (i. e., to calculate) how high (in km) basalt would float in a viscous, flowing upper mantle. Show your work.

The upper surface of oceanic crust in this imaginary world would be about mantle. km above the level of the upper