The part of the earth's crust which is made up of silica and alumina is the_____?

Step 1: Analyze the question The question asks for the layer of the earth's crust made up mainly of silica (Si) and alumina (Al).

Step 2: Explain the concept The earth's crust is divided into two parts, and the names come from their main minerals:

• Sial = Silica + Alumina. This is the upper, lighter layer of the crust. It forms the continents and is mostly granitic rock.
• Sima = Silica + Magnesia (magnesium). This is the lower, denser layer. It underlies the ocean floors and is mostly basaltic rock.

The other options are not parts of the crust:

• Mantle: the layer beneath the crust, rich in iron and magnesium silicates.
• Barysphere (also called the core): the innermost part of the earth, made mostly of nickel and iron (sometimes called Nife).

Step 3: Solve

• Silica and alumina give Si + Al = Sial.
• Sima (A) contains magnesia, not alumina.
• Mantle (B) and Barysphere (C) are not part of the crust.

Step 4: Answer The correct option is D. Sial.

Tip: Read the names as abbreviations of the elements.

• SiAl = Silica + Alumina (continents, on top)
• SiMa = Silica + Magnesia (ocean floors, below)
• NiFe = Nickel + Iron (core)

Remember that Al comes above Ma, because Sial sits on top of Sima.