Chapter 9, Problem 79AP

As a first approximation. Earth's continents may be thought of as granitr blocks floating in a denser rock (called peridotitc) in the same way that ice floats in water. (a) Show that a formula describing this phenomenon is

  ρ_gt = ρ_pd

where ρ_g is the density of granite (2.8 × 10³ kg/m³), ρ_p is the density of peridotite (3.3 × 10³ kg/m³), t is the thickness of a continent, and d is the depth to which a continent floats in the peridotite. (b) If a continent sinks 5.0 km into the peridotite layer (this surface may be thought of as the ocean floor), what is the thickness of the continent?