Inside Our Earth - Class 7

There are three layers inside the earth. 1. Crust, 2. Mantle and 3. Core.

Question: What is earth crust?

Answer:  The uppermost layer of the earth where we are living is called as the crust of the earth.

Question: What are the important characteristics of the earth crust?

  • Crust is thin layer. It is almost 35 km on the continental part and 5 km on the ocean floor area.
  • The continental part of the earth crust is generally made up of silicon (Si) and aluminium(Al), hence this layer is known as ‘SiAl’ layer.
  • The oceanic part of the earth crust is mainly made up of Silicon (Si) and magnesium (ma), hence this layer is known as ‘Sima’.
  • We are living on sial layer and ocean water is on sima layer of the earth crust.
Question: What do you know about mantle? (Inside Our Earth)

Answer: Mantle is the second layer of the earth just beneath the crust.

  • Mantle is extended up to 2900 km from the earth surface.
  • This layer is divided from the earth crust through the layer namely asthenosphere.
  • Mantle is divided into two parts. Upper part of the mantle is known as ‘Crofesima’ and lower part is known as ‘nifesima’.
Q1. Discuss about the earth crust. (Inside Our Earth)
Ans: The upper most layer overthe earth’s surface is called the crust.
  • It is the thinnest of all the layers.
  • It is about 35 km.on the continental masses and only 5 km. on the ocean floors.
  • The main mineral constituents of the continental mass are silica and alumina. It is thus called sial (si-silica and al-alumina).
  • The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium).
Q2. Discuss about the mantle of the interior of the earth.
Ans: Just beneath the crustis the mantle which extends up to a depth of 2900 km. below the crust.
– The upper part of the mantle is called ‘crofesima’ and lower part is called as ‘nifesima’.
Q3. Discuss about the core of the earth.
Ans: The innermost layer is the core with a radius of about 3500 km.
  • It is mainly made up of nickel and iron and is called  nife  (ni  – nickel and  fe  – ferrous i.e. iron).
  • The central core has very high temperature and pressure.
  • The radius of the earth is 6371 km. and core is extended up to this distance.
Q4. What do you mean by rocks? (Inside Our Earth)
Ans: The earth’s crust is made up of various types of rocks. Any natural mass of mineral matter that makes up the earth’s crust is called a  rock. Rocks can be of different colour, size and texture. For example- igneous rocks, sedimentary rocks, metamorphic rocks etc.
Q5. Discuss about different types of rocks.
Ans: There are three major types of rocks:
A) Igneous rocks:
When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called  primary rocks. Basalts, granite etc are the igneous rock.
B) sedimentary rocks:
Rocks roll down, crack, and hit each other and are broken down into small fragments. These materials are transported and deposited by wind, water, etc. and form rocks layer. For example, sandstone is made from grains of sand.
C) metamorphic rocks.
Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble.
Q6. Discuss about the process of sedimentary rock formation.
Ans: Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called  sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks.
For example, sandstone is made from grains of sand. These rocks may also contain fossils of plants, animals and other microorganisms that once lived on them.
Q7. Explain about the rock cycle.
Ans: One type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the  rock cycle.
Igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks. When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks. The metamorphic rocks which are still under great heat and pressure melt down to form molten magma. This molten magma again can cool down and solidify into igneous rocks.

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