GEOLOGY

Detailed explanation-1: -The Earth is covered by two kinds of crust-continental and oceanic. The thinner oceanic crust is normally a little more than four miles thick, while the thicker continental crust is often as much as 25 miles thick. Continental crust is also much less dense than its oceanic counterpart.

Detailed explanation-2: -Continental crust is thickest under mountain ranges, where it bulges downward into the mantle, forming a mountain root. Geophysical data also show that continental crust would “float” on oceanic crust because continental crust is less dense (continental crust, 2.7 g/cm 3; oceanic crust, 3.0 g/cm 3).

Detailed explanation-3: -The crust is thickened by the compressive forces related to subduction or continental collision. The buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, which is where the thickest crust is found.

Detailed explanation-4: -Continental crust is typically 40 km (25 miles) thick, while oceanic crust is much thinner, averaging about 6 km (4 miles) in thickness.

Detailed explanation-5: -Oceanic crust is generally composed of dark-colored rocks called basalt and gabbro. It is thinner and denser than continental crust, which is made of light-colored rocks called andesite and granite. The low density of continental crust causes it to “float” high atop the viscous mantle, forming dry land.