NMMS Unit 1 - Interior of the Earth (7th Standard Geography Term -1)
Based on the text provided in the PDF, here are the comprehensive notes and 30 MCQs tailored for NMMS and TNPSC exam preparation.
Comprehensive Notes: Unit 1 - Interior of the Earth
1. Introduction
The Earth is a dynamic planet undergoing constant changes inside and outside.
The structure of the Earth is compared to that of an apple.
Based on earthquake waves, the Earth is divided into three concentric layers: Crust, Mantle, and Core.
2. Structure of the Earth
A. The Crust (The Outermost Layer)
Thickness: Varies from 5 to 30 km. It is about 35 km on continental masses and 5 km on ocean floors.
Composition:
Continental Crust (SIAL): Made of Granite rocks. Rich in Silica and Alumina. Average density: 2.7 g/Cm3.
Oceanic Crust (SIMA): Made of dense Basalt rocks. Rich in Silica and Magnesium. Average density: 3.0 g/Cm3.
Key Concept: Since Sial is lighter than Sima, continents "float" on the denser Sima.
Fact: The crust forms only 1% of the Earth's volume.
B. The Mantle (The Middle Layer)
Location: Beneath the crust.
Boundary: Separated from the crust by the Mohorovicic discontinuity.
Thickness: About 2,900 km.
Divisions:
Upper Mantle: Extends to 700 km. Density: 3.4 - 4.4 g/Cm3.
Lower Mantle: Extends from 700 to 2,900 km. Density: 4.4 - 5.5 g/Cm3.
Fact: The Mantle forms 84% of the Earth's volume. The Asthenosphere is the part of the mantle that flows and moves the plates.
C. The Core (The Innermost Layer)
Also known as: Barysphere.
Boundary: Separated from the mantle by the Weichart-Gutenberg discontinuity.
Divisions:
Outer Core: Rich in Iron, in a liquid state. Extends 2,900 – 5,150 km.
Inner Core: Composed of Nickel and Ferrous (NIFE). It is in a solid state due to high pressure. Extends 5,150 – 6,370 km.
Density: Average density is 13.0 g/Cm3.
Fact: The Core forms 15% of the Earth's volume.
Earth's Radius: 6,371 km.
3. Earth Movements
Lithospheric Plates: The lithosphere is broken into plates that move independently over the asthenosphere.
Tectonic Movements: The movement of these plates, driven by the Earth's internal heat.
Types of Forces:
Endogenic Forces: Act in the interior (sudden movements like earthquakes/volcanoes).
Exogenic Forces: Work on the surface (slow movements).
Plate Interactions:
Divergent: Plates move away, creating rifts.
Convergent: Plates collide. If oceanic collides with continental, the denser oceanic plate goes below (subduction), causing melting and volcanoes. If two continental plates collide, they fold to form mountains (e.g., Himalayas).
4. Earthquakes
Definition: Sudden shaking or trembling of the Earth's crust.
Key Terms:
Focus (Hypocenter): The point where vibrations originate inside the Earth.
Epicenter: The point on the surface directly above the focus.
Seismic Waves: Travel from the focus. Three types:
P waves: Longitudinal waves.
S waves: Transverse waves.
L waves: Surface waves.
Measurement: Recorded by Seismograph. Magnitude measured by Richter scale (ranges 0 to 9).
Tsunami: A Japanese term for huge sea waves caused by underwater earthquakes. A major Tsunami hit the Indian Ocean on 26th December 2004.
Distribution of Earthquakes:
Circum-Pacific Belt (Pacific Ring of Fire): 68% of earthquakes.
Mediterranean-Himalayan Belt: 31% (includes Himalayas, NW China).
African/Rift Valley Areas: Remaining %.
Earthquakes in India: Himalayan region, Ganga-Brahmaputra valley.
Notable Events: Uttar Kashi (1991), Chamoli (1999), Koyna (1967), Latur (1993).
5. Volcanoes
Definition: A vent or opening through which hot magma erupts.
Terminology:
Magma: Molten rock inside the Earth.
Lava: Molten rock on the surface.
Crater: Funnel-shaped depression at the top.
Caldera: Large basin-shaped crater formed by violent explosions blowing away the top.
Causes: Temperature increases 1°C for every 32 meters depth. Gases in magma force material out.
Scientific Study: Called Volcanology. People who study it are Volcanologists.
Types of Lava Flow:
High Viscosity: Rich in silica, little water (moves slowly).
Low Viscosity: Little silica, lot of water (moves rapidly, smooth flow).
Classification of Volcanoes (by periodicity):
Active Volcanoes: Erupt frequently.
Examples: Mt. Stromboli (Mediterranean), St. Helens (USA), Pinatubo (Philippines), Mauna Loa (Hawaii - World's biggest active volcano).
Barren Island: The only active volcano in India (Andaman Sea), last erupted in 2017.
Note: Mt. Stromboli is called the "Light House of the Mediterranean Sea".
Dormant Volcanoes: Sleeping volcanoes; no recent activity but may erupt.
Examples: Vesuvius (Italy), Mt. Fujiyama (Japan), Mt. Krakatoa (Indonesia).
Extinct Volcanoes: No eruption in past 1000 years.
Examples: Mt. Popa (Myanmar), Mt. Kilimanjaro and Mt. Kenya (Africa).
Volcanic Zones:
Circum-Pacific Belt (Ring of Fire): Coastal Pacific areas. 2/3rds of world's volcanoes.
Mid-Continental Belt: Alpine mountains, Mediterranean, Eastern Africa. (Includes Vesuvius, Stromboli, Etna). Note: Himalayas have no active volcanoes.
Mid-Atlantic Belt: Divergent boundary. Iceland is the most active area here.
30 Multiple Choice Questions (MCQs)
The structure of the Earth is scientifically compared to which fruit?
A) Orange
B) Apple
C) Watermelon
D) Mango
The average density of the Sial layer is:
A) 3.0 g/Cm3
B) 5.5 g/Cm3
C) 2.7 g/Cm3
D) 13.0 g/Cm3
What is the boundary separating the Crust and the Mantle called?
A) Weichart-Gutenberg discontinuity
B) Mohorovicic discontinuity
C) Conrad discontinuity
D) Lehmann discontinuity
Which layer constitutes 84% of the Earth's volume?
A) Crust
B) Core
C) Mantle
D) Inner Core
The innermost layer of the Earth (Core) is also known as:
A) Lithosphere
B) Barysphere
C) Asthenosphere
D) Mesosphere
Sima is rich in which two minerals?
A) Silica and Alumina
B) Silica and Magnesium
C) Nickel and Ferrous
D) Iron and Magnesium
The radius of the Earth is approximately:
A) 6,371 km
B) 5,150 km
C) 2,900 km
D) 7,000 km
The instrument used to record earthquake waves is:
A) Barometer
B) Seismograph
C) Thermometer
D) Richter Scale
The point on the Earth's surface directly above the earthquake focus is called:
A) Hypocenter
B) Crater
C) Epicenter
D) Vent
In which year did the devastating Tsunami hit the Indian Ocean?
A) 2000
B) 2004
C) 2011
D) 1999
Which belt is known as the "Pacific Ring of Fire"?
A) Mid-Continental Belt
B) Mid-Atlantic Belt
C) Circum-Pacific Belt
D) Alpine Belt
Mauna Loa, the world's biggest active volcano, is located in:
A) Japan
B) Indonesia
C) Hawaii
D) Italy
Which volcano is known as the "Light House of the Mediterranean Sea"?
A) Mt. Vesuvius
B) Mt. Stromboli
C) Mt. Etna
D) Mt. Fujiyama
The only active volcano in India is located in:
A) Lakshadweep
B) Barren Island
C) Puducherry
D) Minicoy
The inner core of the Earth is in which state?
A) Liquid
B) Gas
C) Solid
D) Semi-molten
Temperature inside the Earth increases at the rate of 1°C for every ______ meters.
A) 32
B) 64
C) 100
D) 165
Which of the following is an example of an Extinct Volcano?
A) Mt. Fuji
B) Mt. Popa
C) Mt. St. Helens
D) Mt. Stromboli
The Earth's crust is thinnest under the:
A) Mountains
B) Plateaus
C) Continents
D) Oceans
What is the approximate thickness of the Mantle?
A) 700 km
B) 2,900 km
C) 5,150 km
D) 6,370 km
The Koyna earthquake occurred in which year?
A) 1993
B) 1967
C) 1991
D) 1999
The movement of lithospheric plates is termed as:
A) Volcanic movement
B) Tectonic movement
C) Weathering
D) Erosion
Which of the following waves are also called Surface Waves?
A) P waves
B) S waves
C) L waves
D) T waves
If the crater of a volcano is very large and basin-shaped, it is called a:
A) Vent
B) Caldera
C) Fissure
D) Cone
Which mountain range was formed by the collision of two continental plates?
A) Andes
B) Rockies
C) Himalayas
D) Alps
The Richter scale measures the ______ of an earthquake.
A) Direction
B) Magnitude
C) Speed
D) Time
Which of the following minerals makes up the core (NIFE)?
A) Nickel and Iron
B) Nitrogen and Iron
C) Nickel and Ferrous
D) Nitrogen and Ferrous
Volcanoes that have shown no sign of activity for many years but may become active are called:
A) Active
B) Extinct
C) Dormant
D) Dead
Iceland is located on which volcanic belt?
A) Circum-Pacific Belt
B) Mid-Continental Belt
C) Mid-Atlantic Belt
D) Alpine-Himalayan Belt
The upper part of the mantle extends down to:
A) 2,900 km
B) 700 km
C) 5,150 km
D) 35 km
Which region in India experienced a severe earthquake in 1993?
A) Chamoli
B) Uttar Kashi
C) Latur
D) Bhuj
Answer Key
B (Apple)
C (2.7 g/Cm3)
B (Mohorovicic discontinuity)
C (Mantle - 84%)
B (Barysphere)
B (Silica and Magnesium)
A (6,371 km)
B (Seismograph)
C (Epicenter)
B (2004)
C (Circum-Pacific Belt)
C (Hawaii)
B (Mt. Stromboli)
B (Barren Island)
C (Solid)
A (32 meters)
B (Mt. Popa)
D (Oceans - 5km)
B (2,900 km)
B (1967)
B (Tectonic movement)
C (L waves)
B (Caldera)
C (Himalayas)
B (Magnitude)
C (Nickel and Ferrous)
C (Dormant)
C (Mid-Atlantic Belt)
B (700 km)
C (Latur)