Th earth's crust consists essentially of?

The question is asking about the composition of the Earth's crust. The Earth's crust is the outermost layer of the Earth, and it is made up of different elements.

The options given are:

- Option A: magnesium and silica

- Option B: silica and aluminium (Correct)

- Option C: calcium and aluminium

- Option D: magnesium and calcium

To determine the correct answer, we need to know the main elements that make up the Earth's crust. The Earth's crust is primarily composed of silica and aluminium, which are found in Option B. Therefore, the correct answer is Option B: silica and aluminium.

Silica is a compound made up of silicon and oxygen, and it is a major component of many minerals found in the Earth's crust. Aluminium is a metal that is also commonly found in the Earth's crust. These two elements make up a significant portion of the composition of the Earth's crust.

It's important to note that while magnesium and calcium are also present in the Earth's crust, they are not the primary components. The main elements that make up the Earth's crust are silica and aluminium.

Understanding the composition of the Earth's crust is essential in studying geology and understanding the processes that shape the Earth's surface. By studying the different elements present in the Earth's crust, scientists can gain insights into the formation of rocks, mountains, and other geological features.

In summary, the Earth's crust consists primarily of silica and aluminium, making Option B the correct answer.