On average, Earth's crust and upper mantle has a density of about 3.0
g/cm^3.  If Earth shrinks in size by 0.1 meter in radius, the gravitational
potential energy of the top layer of our planet would be converted into
heat.  Think of it as a layer of the planet falling 0.1 meter.

(a) About how much energy would be released if such a shrinkage occurred?
You will need to know the mass of the layer of Earth that falls, the
distance it falls, and Earth's gravitational acceleration at its surface.

(b) How does this compare to the total energy released by the atomic
bomb detonated over Hiroshima?  This energy is, of course, spread out
over the entire planet; would we notice it?  Again, use numerical common
sense in your answer.