Question

The lower part of the crust known as ‘Oceanic Crust’ is rich in _____
A. Aluminium and copper
B. Magnesium and aluminium
C. Copper and gold
D. Silica and magnesium

Answer 1

Hint: Oceanic crust, the outermost layer of Earth's lithosphere that is found under the oceans and formed at spreading centres on oceanic ridges, which occur at divergent plate boundaries. It is also called 'sima' because of the elements it contains. Since it is the lower layer, it is more likely to have heavier minerals.

Complete answer:
The Earth is divided into three primary layers- The crust, the mantle and the core. These layers are further divided into subparts. The crust is divided into the continental and oceanic crust. This division is based on the chemical composition of these layers as well as the other properties. The oceanic crust is the lower part of the crust. Let us see which of the given elements are most abundant in the oceanic crust.-

A. Aluminium and copper are not most commonly found in the Oceanic floor. Instead, aluminium is found mostly in the continental crust and copper is present in all parts of the crust. Thus, this is not the correct answer.

B. Magnesium and aluminium are not the main constituents of the oceanic crust. While magnesium is abundant in this part of the crust, aluminium is not. So, this is also not the correct answer.

C. Copper and Gold are not richly present in only the oceanic crust either. Both these elements are found in different spots in both the layers of the crust.

D. Silica and magnesium are the most abundantly found elements in the oceanic crust. This is the reason why the layer is also called SiMa (Silicon and Magnesium). Therefore, this is the correct answer.

Therefore, the correct answer is Option ‘D’.

Note:
i) Since the Oceanic crust is the lowest layer of the crust, it is also called the basal layer.
ii) Similar to the oceanic crust being called SiMa, the continental crust is also called SiAl due to the presence of Silica and Aluminium.
iii) The oceanic crust is denser than the continental crust.
iv) When SiMa comes to the surface of the earth due to geological processes like volcanic eruptions or faulting, it most often takes the form of basalt.