Question

which of the following statements about earths crust is true? the oceanic crust is mostly composed of basalt, while the continental crust is mostly composed of granite. the oceanic crust is typically older than the continental crust. the continental crust is denser than the oceanic crust. the continental and oceanic crusts have the same thickness.

Explanation:

• Oceanic crust composition: Oceanic crust is mainly basalt. Basalt is a fine - grained, dark - colored igneous rock formed from the rapid cooling of lava at the ocean floor.
• Continental crust composition: Continental crust is mainly granite. Granite is a coarse - grained, light - colored igneous rock formed from the slow cooling of magma beneath the Earth's surface.
• Age comparison: Oceanic crust is generally younger than continental crust. New oceanic crust is constantly formed at mid - ocean ridges through volcanic activity, while continental crust has been around for a very long time (some parts are over 3 billion years old).
• Density comparison: Oceanic crust is denser (about \(3.0\ g/cm^{3}\)) than continental crust (about \(2.7\ g/cm^{3}\)). This density difference is one of the reasons why oceanic crust subducts (dives beneath) continental crust at convergent plate boundaries.
• Thickness comparison: Oceanic crust is thinner (about 5 - 10 km) compared to continental crust (about 30 - 70 km).

Answer:

The oceanic crust is mostly composed of basalt, while the continental crust is mostly composed of granite.