How do continental crust and oceanic crust differ in composition and thickness?

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volcanology — Earth sciences Geologist using a rock hammer to sample active pahoehoe lava for geochemical analysis on the Kilauea volcano, Hawaii, June 26, 2009.

The continental and oceanic crusts differ significantly in their physical and chemical properties, which dictates their buoyancy and elevation on Earth's surface.

Composition

The continental crust is primarily granitic in composition, resulting in a lower density of approximately 2.7 grams per cubic cm. In contrast, the oceanic crust is basaltic, meaning it is richer in iron and magnesium. This composition gives oceanic crust a higher density, typically ranging from 2.9 to 3 grams per cubic cm.1

Thickness and Elevation

These density differences influence how the crusts interact with the underlying mantle:

Thickness: Continental crust is significantly thicker, averaging about 40 km (25 miles), whereas oceanic crust is much thinner, averaging only about 6 km (4 miles).1
Elevation: Due to its lower density and greater buoyancy, continental crust floats higher in the mantle, maintaining an average elevation of 840 metres (2,750 feet) above sea level. The denser oceanic crust sits much lower, at an average depth of 3,790 metres (12,400 feet) below sea level.1