UPSC, SSC Structure of the Earth Questions and Answers - 1

Question: 1

Explain the terms SIAL and SIMA?

SIAL: It is the outer layer of the earth’s crust. It is composed of rocks rich in Silica and Aluminium. So, it is called SIAL taking “SI” from “Silica” and “AL” form “Aluminum”. Its density is lighter. It is exposed on the continents.

SIMA: It is composed of layers of the earth’s crust below SIAL. It is composed of layers having materials rich in Silica and Magnesium. So, it is called SIMA, taking “SI” from “Silica” and “Ma” from Magnesium. It extends up to a depth of 2900 kms. Its density is higher than SIAL because density increases with depth. It forms the floor of the oceans.

Question: 2

Why is the inner core solid?

The inner core has a thickness about 1220 kms. It is made up of a solid mass of iron and nickel with a temperature of about 4000°C. It is under such extreme pressure that it remains solid.

Question: 3

What are SAIL rocks?

The less dense and light SAIL materials floated over the dense and heavy SIMA materials, when they were in molten stage. When they solidified, SIAL rocks formed the upper layer and SIMA rocks formed the lower layer. They are in segments on top of the SIMA.

Question: 4

Describe briefly about the asthenosphere?

The top layer of the upper mantle 100 to 200 kms is known as asthenosphere. This layer has physical properties that are different from the rest of the upper mantle.

Question: 5

What is the composition of mantle rocks?

The mantle surrounds the core and has a thickness of 2900 kms. It is composed of iron, magnesium, aluminium, silicon and oxygen silicate compounds.