Which term is used for the upper part of Earth's crust rich in silica and aluminum?

Which term is used for the upper part of Earth's crust rich in silica and aluminum?

• A. Rock
• B. Shield Volcano
• C. Run-off
• D. Sial

Answer: (D)

Sial refers to the upper part of the Earth's crust that is rich in silica and aluminium. This composition characterizes the continental crust, which is made mainly of granitic rocks that are light in color and less dense than the oceanic crust. The term contrasts with sima, which is the lower crust portion richer in magnesium and iron and more dense. So, the correct term specifically naming the silica-aluminium-rich upper crust is sial. The other options don’t describe crust composition: rock is a general term for any solid mineral material; shield volcano is a type of volcano; run-off is water movement on the surface.

Sial refers to the upper part of the Earth's crust that is rich in silica and aluminium. This composition characterizes the continental crust, which is made mainly of granitic rocks that are light in color and less dense than the oceanic crust. The term contrasts with sima, which is the lower crust portion richer in magnesium and iron and more dense. So, the correct term specifically naming the silica-aluminium-rich upper crust is sial. The other options don’t describe crust composition: rock is a general term for any solid mineral material; shield volcano is a type of volcano; run-off is water movement on the surface.