The Interior of the Earth Chapter Notes | Window on the Word Class 7: Solutions, Notes & Worksheets PDF Download

The Layers of the Earth

• The Earth is a large spherical rock.
• Beneath its surface lie different layers, similar to the layers of an onion.
• These layers are concentric, meaning they are arranged one inside the other.
• Scientists have discovered that the Earth is not solid all the way through; it consists of various layers.

Crust:

• The crust is the outermost layer of the Earth and forms its surface.
• It is the thinnest of the three layers.
• The crust can be divided into two parts: the continental crust and the oceanic crust.

Continental Crust:

• Forms the continents and extends to a depth of 35 to 70 km.
• Composed mainly of silica and aluminium, it is known as sial.

Oceanic Crust:

• Makes up the ocean floor and extends to a depth of 5 to 10 km.
• Thinner and denser than the continental crust.
• Composed mainly of silica and magnesium, it is termed sima.

Earth's Layers

• The mantle lies beneath the Earth's crust and is approximately 2,900 km thick.
• Comprising more than three-fourths of Earth's volume, it consists of silica, iron, magnesium, and aluminum.
• The mantle is divided into the upper mantle and the lower mantle, with most of it being semi-solid molten rock known as magma.
• Temperature in the mantle ranges between 650 and 1200 degrees Celsius.
• The core is the innermost layer of the Earth with a radius of about 3,500 km.
• It is primarily composed of nickel and iron, also known as nife.
• The core is further classified into the outer core (liquid) and the inner core (solid under extreme pressure).
• Temperatures in the core are estimated to exceed 5000 degrees Celsius.

Rocks

• The Earth's crust consists of hard, solid materials known as rocks.
• Rocks vary in colors, sizes, and textures. They can be classified into three main groups: igneous, sedimentary, and metamorphic.
• Magma moves upward towards the Earth's crust, cools, and solidifies to form rocks, known as igneous rocks.
• Igneous rocks, also referred to as primary rocks, can be further categorized into two groups.

Igneous Rocks

• Magma that flows out onto the surface of the Earth through volcanic eruptions is known as lava.
• When lava cools and solidifies, it forms extrusive rocks.
• Extrusive rocks are very finely grained and sometimes even glassy due to the fast cooling of lava.
• Intrusive igneous rocks are formed when magma is trapped under the crust, cools down, and solidifies.
• These rocks form large crystals and have a coarse structure as the cooling process takes place slowly beneath the Earth's surface.

Sedimentary Rocks:

• Rocks break down into sediment over time.
• Sediment is carried by wind and water, then deposited in various locations.
• Through compression and hardening, sediment forms sedimentary rocks.
• These rocks, also known as stratified rocks, are formed in layers.
• Sedimentary rocks are generally more porous and softer than igneous rocks.
• Limestone is an example of a sedimentary rock.
• Fossils are commonly found in sedimentary rocks.

Metamorphic Rocks:

• Under heat and pressure, igneous and sedimentary rocks can change into metamorphic rocks.
• For instance, limestone can transform into marble when subjected to intense heat and pressure.

Minerals

• Rocks consist of various naturally occurring substances known as minerals.
• Each mineral possesses a unique chemical composition and specific physical properties.

Classification of Minerals

Minerals are broadly categorized into two main types:

Metallic Minerals

• Generally found in igneous rocks.
• Rocks rich in metallic minerals are termed as ores.
• Examples include iron ore, copper, and bauxite.

Non-Metallic Minerals

• Primarily found in sedimentary rocks.
• Examples encompass limestone, mica, and kaolinite.

Rock Cycle

• Formation of all rocks begins with magma deep inside the Earth.
• Magma cools to form igneous rocks.
• Igneous rocks are brought to the Earth's surface by geological movements like folding and faulting.
• Over time, rocks break down due to weathering and erosion, forming sediments.
• Water, wind, or ice transport sediments to various locations where they are deposited in layers.
• With time, sediments accumulate, get compressed, and harden to form sedimentary rocks.
• Under conditions of high temperature and pressure, igneous and sedimentary rocks can transform into metamorphic rocks.
• Movements of the Earth may push metamorphic rocks deep into the mantle where they can revert to molten magma, solidifying again into igneous rocks.
• This continuous process, where one type of rock changes into another, is known as the rock cycle.

Fossil Fuels

• Fossil fuels, crucial energy sources, are located in sedimentary rocks.
• They originate from the decomposition of ancient fossils, plants, and animals that were buried deep in the Earth's crust millions of years ago.

Uses of Rocks, Minerals, and Fossil Fuels

Rocks, minerals, and fossil fuels are essential natural resources with various important applications.

Uses of Rocks

• Rocks are primarily utilized in construction for building blocks, cement, and concrete.
• Marble and soapstone, types of rocks, are commonly used in sculpting.

Uses of Minerals

• Minerals serve as sources for significant metals like iron, gold, aluminum, copper, and silver.
• Iron ore, a mineral, is crucial in steel production.

Uses of Fossil Fuels

• Fossil fuels are the primary source of energy for various activities such as cooking, transportation, and industrial operations.