Samacheer Class 7 Social Science - Interior of the Earth

Weichart – Gutenberg discontinuity
2. The earthquake waves are recorded by an instrument known as ……………….
Seismograph

3. Magma rises to the surface and spreads over a vast area is known as ……………….
Lava
4. An example for active volcano ……………….
Mauna Loa in Hawaii /Mt. Strampoli / St. Helens / Pinatubo
5. Seismology is the study of ……………….
Earthquakes

1. A. Japanese term
2. B. Africa
3. D. Silica and magnesium

1. Earth quake
c) Sudden movement
2. Sima
d) Silica and magnesium
3. Pacific Ring of Fire
e) World volcanoes
4. Tsunami
a) Japanese term
5. Mt. Kenya
b) Africa

The chief cause of the Earthquake is the sudden slipping of the portion of the earth’s crust along with fractures or faults.
The sudden shifting of landmass causes upheavals.
Volcanic activity

The innermost layer of the earth is called the core. It is also known as the barysphere. It is separated from the mantle by a boundary called Weichart-Gutenberg discontinuity. The core is also divided into two parts.
The outer core, which is rich in iron, is in the liquid state.
The inner core, composed of Nickel and Ferrous (Nife), is solid in the state.

The innermost layer of the earth is called the core. The central core has very high temperature and pressure. So no one has been able to take samples from the interior of the earth.

Despite the greater thickness, the continental crust is less dense than the oceanic crust because it is made of both light and dense rock types.

SIAL
SIAL is the upper part of the crust
Consists of granite rocks
Forms the continents
Silica and Alumina are the main mineral constituents.
SIMA
SIMA is the lower part of the crust
Consists of denser basaltic rocks
Forming the ocean floors.
Silica and Magnesium are the main mineral constituents.

Active Volcano
Volcanoes that erupt frequently are called active volcanoes.
600 active volcanoes in the world.
Ex: Mt. Stromboli, St. Helens, Pinatubo, Mauna Loa
DormantVolcano
Volcanoes have no sign of activity for many years but may become active at any time.
Also called sleeping Volcano
Ex: Vesuvius Mountain, Mt. Fujiyama, Mt. Krakatoa

Earthquakes may cause changes in the earth’s surface. They are
Vibrations often set landslides in mountainous regions.
Falling of buildings is another danger of earthquakes.
Most of the houses which collapsed were made of mud and bricks and proved to be death traps.
Fire is another great danger.
The underground water system is disturbed.
Causes great disturbance in the water.
The floods and waves cause great loss of life.

There are three types of Volcanoes based on eruptions.
Active Volcanoes
Dormant Volcanoes
Extinct Volcanoes
Active Volcanoes:
It erupts frequently. Most of them lie in the Pacific Ring of Fire belt.
There are about 600 active Volcanoes in the world. Mauna Loa in Hawaii is the world’s biggest active Volcano.
Ex: Mt. Stromnoli, St. Helens, Pinatubo.
Dormant Volcanoes:
It has shown no sign of activity for many years but they may become active at any time.
It is also called a sleeping Volcano.
Ex: Vesuvius mountain, Mt. Fujiyama, Mt. Krakatoa.
Extinct Volcanoes
The top of extinct Volcanic mountains has been eroded.
Ex: Mt. Popa, Mt. Kilimanjaro and Mt. Kenya.

There are three major zones of volcanic activities in the world. They are:
The Circum – Pacific belt
The Midcontinental belt
The Mid Atlantic belt
Circum Beit
This is the volcanic zone of the convergent oceanic plate boundary. It includes the volcanoes of the eastern and western coastal areas of the Pacific Ocean. This zone is popularly termed as the Pacific Ring of Fire which has been estimated to include two-thirds of the world’s volcanoes

The temperature increases at the rate of 10°C for every 35 meters with pressure.
So the interior of the earth is in a semi-molten state called magma.
The magma under great pressure dissolves great volume and combustible gases.
This makes volcanic material burst forth through the weak spots in the earth’s crust.

Distribution of Earthquakes:
In the pacific ring of fire 68% of earthquakes occur. Another 31% of earthquakes take place in the Mediterranean – Himalayan belt and Asia minor.
The remaining percent of earthquakes occur in NorthemAfrica and Rift Valley areas, Ganga – Brahmaputra Valley.

Distribution of Volcanoes:
Volcanoes are located in regions which are intensely folded or faulted.
They are about 600 active volcanoes and thousands of dormant and extinct ones.
They occur along with the coastal mountain ranges, like offshore islands and the midst of oceans.
The Volcanic belts are the principal earthquake belts of the world.
Posted in Class 7 on September 29, 2024 September 30, 2024
Leave a Reply Cancel reply
You must be logged in to post a comment.
Facebook
Twitter
Instagram
Pinterest
Copyright © 2026 Samacheer Kalvi

The innermost layer of the earth, called the core has two parts, the outer core, and the inner core.
The outer core is rich in iron and is in a liquid state.
The inner core is made of Nickel and Ferrous which are in a solid-state.
The central core has a very high temperature and pressure

Volcanoes are constructive and Destructive.
Constructive effects:
Volcanoes provide nutrients to the surrounding soil as volcanic ash contains minerals beneficial to plants.
Some plateaus and plains are formed due to volcanic eruptions.
They cool off the earth removing heat from the interior.
Destructive effects:
They cause earthquakes, fast floods, mudslides, and rockfalls.
Dust and Ash that come out of volcanoes are very harmful to living things.

Some volcanoes are found under oceans. If an underwater volcano keeps erupting, it can rise above the ocean’s surface and thus as Island is formed.
7th Social Science Guide Interior of the Earth Additional Important Questions and Answers