NCERT Class 7 Geography — Chapter 1: Inside Our Earth

mcqeasy

With reference to the composition of the Earth’s crust, the term ‘Sial’ refers to which of the following combinations?

Official previous-year question

Verified 1 Aug 2026.

Options

ASilica and Alumina
BSilica and Iron
CSilica and Magnesium
DSilica and Nickel

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Solution

The correct option is

Silica and Alumina

Explanation

The Earth's interior is chemically differentiated into distinct layers based on the abundance of specific elements. Historically, geologists like Edward Suess classified these layers into Sial, Sima, and Nife based on their mineral composition.

Detailed Analysis:

Sial: The term is derived from the first two letters of Silica (Si) and Alumina (Al). This combination constitutes the upper layer of the Earth's crust. It is less dense than the underlying layers and primarily forms the continental crust, which consists largely of granitic rocks.
Sima: This term refers to a combination of Silica (Si) and Magnesium (Ma). It constitutes the lower crust and is the primary component of the oceanic crust, consisting mainly of denser basaltic rocks.
Nife: This refers to the innermost layer (Core), composed of Nickel (Ni) and Ferrous (Fe) (Iron).

Key Takeaway: Sial refers to the Silica and Alumina-rich continental crust, whereas Sima refers to the Silica and Magnesium-rich oceanic crust.

Your note

More from Chapter 1: Inside Our Earth

Consider the following statements regarding the interior of the Earth: 1. The crust is the thickest layer of the Earth. 2. The oceanic crust is thinner than the continental crust. 3. The mantle extends up to a depth of only 100 km. Which of the statements given above is/are correct?

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Consider the following statements regarding the Earth's core: 1. It is the innermost layer with a radius of about 3500 km. 2. It is mainly composed of silica and magnesium. 3. It has very high temperature and pressure. Which of the statements given above is/are correct?

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Which of the following correctly represents the volume composition of the Earth’s layers?

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The oceanic crust mainly consists of which of the following mineral constituents?

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Consider the following pairs regarding rock types and their word origins: 1. Igneous : Latin word meaning 'fire' 2. Sedimentary : Latin word meaning 'settle down' 3. Metamorphic : Greek word meaning 'change of form' 4. Fossils : Latin word meaning 'hard rock' How many of the above pairs are correctly matched?

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The correct option is

Silica and Alumina

Explanation

Detailed Analysis:

Sial: The term is derived from the first two letters of Silica (Si) and Alumina (Al). This combination constitutes the upper layer of the Earth's crust. It is less dense than the underlying layers and primarily forms the continental crust, which consists largely of granitic rocks.
Sima: This term refers to a combination of Silica (Si) and Magnesium (Ma). It constitutes the lower crust and is the primary component of the oceanic crust, consisting mainly of denser basaltic rocks.
Nife: This refers to the innermost layer (Core), composed of Nickel (Ni) and Ferrous (Fe) (Iron).

Key Takeaway: Sial refers to the Silica and Alumina-rich continental crust, whereas Sima refers to the Silica and Magnesium-rich oceanic crust.