If the continental crust were thinner than its average thickness of 40 km, would it depress the mantle more or less than it does now? Explain.
To understand whether a thinner continental crust would depress the mantle more or less than its current state, we need to look at the concept of isostasy. Isostasy is the equilibrium that exists between Earth's lithosphere (which includes the crust and the rigid uppermost part of the mantle) and the asthenosphere (which is a more ductile part of the upper mantle).
The principle of isostasy states that areas of higher elevation, like mountains and continents, tend to "float" on the denser asthenosphere below, while areas of lower elevation, like ocean basins, sink into the asthenosphere to maintain balance. This is primarily due to the differences in density between the continental crust and the underlying mantle.
Now, let's consider the scenario where the continental crust is thinner than its average thickness of 40 km. In this case, the overall density of the crust would be lower than before because there is less mass present. Remember, density is calculated by dividing the mass of an object by its volume.
With a lower density, the thinner continental crust would exert less buoyancy on the underlying mantle compared to a thicker crust. This means that the mantle beneath the thinner crust would experience less compression or depression.
In simpler terms, with a thinner continental crust, there would be less weight pressing down on the mantle, resulting in a smaller depressional effect. So, if the continental crust were thinner than its average thickness, it would depress the mantle less than it does now.