Theory & Concepts
Master Physical Geography (Solar System, Earth, Atmosphere) for SSC CGL
Get comprehensive theory, expert shortcuts, and hand-picked practice questions for Physical Geography (Solar System, Earth, Atmosphere) specifically designed for the SSC CGL 2025-26 pattern.
25+
Exams Covered
100+
Study Modules
5K+
Practice Notes
45 min readGK: GeographyWeightage: High
Physical Geography: Solar System, Earth's Structure & Atmosphere
Physical Geography is a cornerstone of the General Awareness section in the SSC CGL examination. It covers the fundamental dynamics of our planet, including the composition of the Solar System, the Earth's interior layering, atmospheric stratification, global wind circulation, and key geomorphological processes. This guide outlines high-yield concepts and facts tailored to the latest CGL patterns.
Learning path
- Solar System & Planetary Dynamics
- Earth's Interior & Discontinuities
- Atmosphere, Pressure Belts & Local Winds
- 20 Premium Practice Questions
1. The Solar System & Earth Movements
The Solar System consists of the Sun and the celestial bodies bound to it by gravity. Understanding the classifications and distinct features of planets is essential:
- Inner Planets (Terrestrial / Rocky): Mercury, Venus, Earth, and Mars. They have dense, rocky compositions and few or no moons.
- Outer Planets (Jovian / Gas Giants): Jupiter, Saturn, Uranus, and Neptune. They are composed mostly of gases and ice, possess extensive ring systems, and have many moons.
- Venus: The hottest planet (due to a runaway greenhouse effect from dense CO₂ atmosphere). It is also the brightest planet, known as the "Morning Star", "Evening Star", and "Earth's Twin" (due to similar size and mass). It rotates clockwise (retrograde rotation).
- Mars: Known as the "Red Planet" due to the presence of iron oxide on its surface. It has two natural satellites: Phobos and Deimos.
- Jupiter & Saturn: Jupiter is the largest planet and has the shortest day (fastest rotation). Its moon Ganymede is the largest satellite in the solar system. Saturn is known for its spectacular ring system and its largest moon Titan, which has a dense atmosphere.
Earth's Rotation and Revolution
The Earth exhibits two primary motions that dictate seasonal and diurnal patterns:
- Rotation: The Earth spins on its axis from West to East once every 24 hours. This causes day and night and generates the Coriolis Effect (deflection of winds).
- Revolution: The Earth orbits the Sun in an elliptical path once every 365.25 days. Combined with the axial tilt of 23.5°, revolution causes seasons and changing lengths of day and night.
- Solstice:
- Summer Solstice (June 21): The Northern Hemisphere is tilted towards the Sun, resulting in the longest day of the year in the north.
- Winter Solstice (December 22): The Southern Hemisphere is tilted towards the Sun, making it the shortest day in the Northern Hemisphere.
- Equinox: The Sun shines directly over the Equator, resulting in equal day and night lengths globally. Occurs on March 21 (Vernal/Spring Equinox) and September 23 (Autumnal Equinox).
- Orbital Extremes: Perihelion is when Earth is closest to the Sun (approx. Jan 3), and Aphelion is when Earth is farthest from the Sun (approx. July 4).
Visualizing Earth's orbital positions showing Equinoxes (equal day/night) and Solstices (maximum tilt towards/away from the Sun).
2. Internal Structure of the Earth
The Earth's interior is chemically and mechanically stratified. The chemical layers consist of:
- Crust: The outermost solid layer, subdivided into the continental crust (composed of SIAL - Silica & Aluminium) and the oceanic crust (composed of SIMA - Silica & Magnesium).
- Mantle: Extends down to 2,900 km, representing about 84% of the Earth's volume. Its upper section contains the Asthenosphere, which is semi-fluid (plastic) and the primary source of volcanic magma.
- Core: The innermost layer, composed mainly of Nickel and Iron (NIFE). The outer core is liquid (responsible for Earth's magnetic field), and the inner core is solid due to extreme pressure.
Visualizing the chemical layers (Crust, Mantle, Core) and physical discontinuities of the Earth.
Seismic Discontinuities
Boundary zones separating distinct layers are marked by rapid changes in seismic wave velocities. Candidates must memorize these transitions:
| Discontinuity Name | Separates Layer A | From Layer B |
|---|---|---|
| Conrad | Upper Crust | Lower Crust |
| Mohorovicic (Moho) | Crust | Mantle |
| Repetti | Upper Mantle | Lower Mantle |
| Gutenberg | Mantle | Outer Core |
| Lehmann | Outer Core | Inner Core |
Rocks Classification
Rocks are classified into three major groups based on their mode of origin:
- Igneous Rocks: Formed by the cooling and solidification of molten rock (magma/lava). Examples: Granite, Basalt, Gabbro, and Pumice. Basil/Basalt is a major constituent of the oceanic crust.
- Sedimentary Rocks: Formed by the deposition, compaction, and cementation of mineral and organic particles over time. They often contain fossils. Examples: Sandstone, Limestone, Shale, Conglomerate, and Coal.
- Metamorphic Rocks: Formed when existing rocks undergo mineralogical and structural changes due to intense heat and pressure (without melting). Examples: Marble (from Limestone), Quartzite (from Sandstone), Slate (from Shale), and Gneiss (from Granite).
3. Atmosphere, Pressure Belts & Local Winds
The Earth's atmosphere is a protective envelope of gases. It consists primarily of Nitrogen (78%), Oxygen (21%), Argon (0.93%), and Carbon Dioxide (0.04%).
Visualizing the five major layers of the Earth's atmosphere (Troposphere to Exosphere).
Atmospheric Layers
The atmosphere is divided vertically into five layers based on temperature variations:
- Troposphere: The lowest layer where all weather phenomena (clouds, rain, storms) occur. It contains 75% of the atmosphere's mass. Temperature decreases with altitude at the rate of approximately 6.5°C per km (Normal Lapse Rate).
- Stratosphere: Extends up to 50 km. It is free from weather disturbances and clouds, making it ideal for flying commercial jet aircraft. It contains the Ozone Layer (Ozonosphere), which absorbs harmful solar Ultraviolet (UV) radiation. Temperature increases with height here.
- Mesosphere: Extends up to 80 km. It is the coldest layer of the atmosphere (temperatures drop to -100°C). Meteors burn up in this layer upon entering from space.
- Thermosphere (includes Ionosphere): Extends from 80 to 400 km. It contains electrically charged ions that reflect radio signals back to Earth, enabling wireless communication. Temperature rises rapidly with height.
- Exosphere: The uppermost layer, which gradually merges with outer space. It is composed of extremely low-density light gases like Hydrogen and Helium.
Global Pressure Belts & Winds
Differential solar heating sets up permanent high and low-pressure belts across the globe:
- Equatorial Low (Doldrums): Located between 5°N and 5°S. Characterized by intense heating, rising air, and calm winds.
- Subtropical Highs (Horse Latitudes): Located around 30°N and 30°S. Characterized by descending dry air, clear skies, and calm conditions.
- Planetary Wind Systems:
- Trade Winds: Blow from the Subtropical Highs towards the Equatorial Low.
- Westerlies: Blow from the Subtropical Highs towards the Subpolar Lows.
- Polar Easterlies: Blow from the Polar Highs towards the Subpolar Lows.
Visualizing the Earth's global pressure belts (low and high pressure zones) and the resulting planetary wind systems (Trades, Westerlies, and Easterlies).
Important Local Winds
Local winds are periodic or seasonal winds generated by localized temperature and pressure differences. These are frequently tested in CGL:
Chinook (Rockies, USA/Canada)
A warm, dry wind blowing down the eastern slopes of the Rocky Mountains. Known as the "Snow Eater" because it melts winter snow cover quickly.
Loo (Northern India / Pakistan)
A hot, dry, and dusty summer wind that blows across the Indo-Gangetic plains during May and June, causing heatwaves.
Harmattan (West Africa)
A dry, dusty wind blowing from the Sahara desert towards the Gulf of Guinea. Known as "The Doctor" due to its dry and relative health-promoting qualities compared to damp tropical air.
Sirocco (Sahara to Mediterranean)
A warm, dry, and dusty wind originating in the Sahara and blowing north across the Mediterranean Sea to Southern Europe, often bringing "blood rain" (red dust).
4. Practice Questions (20 Premium Solved Questions)
Question 01CGL Pattern
Which planetary satellite in the Solar System is the largest in size, even larger than the planet Mercury?
A) Titan
B) Ganymede
C) Phobos
D) Triton
Correct answer: B) Ganymede
Step-by-step Solution
Step 1: Compare the sizes of the largest moons. Ganymede is the largest natural satellite in the Solar System.
Step 2: Ganymede is a moon of Jupiter and has a diameter of 5,268 km, making it larger than the planet Mercury (diameter 4,879 km).
Step 3: Titan (moon of Saturn) is the second largest, and also larger than Mercury.
Conclusion: The correct option is B.
Question 02CGL Pattern
The Mohorovicic discontinuity (Moho) forms the boundary between which two layers of the Earth?
A) Upper Crust and Lower Crust
B) Crust and Mantle
C) Mantle and Core
D) Outer Core and Inner Core
Correct answer: B) Crust and Mantle
Step-by-step Solution
Step 1: Recall the order of discontinuities from outer to inner: Conrad, Mohorovicic, Repetti, Gutenberg, Lehmann.
Step 2: Conrad separates upper and lower crust.
Step 3: Mohorovicic separates the Earth's Crust from the underlying Mantle.
Conclusion: Option B is correct.
Question 03CGL Pattern
Which layer of the atmosphere contains the Ozone Layer that absorbs harmful solar ultraviolet rays?
A) Troposphere
B) Stratosphere
C) Mesosphere
D) Ionosphere
Correct answer: B) Stratosphere
Step-by-step Solution
Step 1: The Ozone Layer (Ozonosphere) is located primarily in the lower portion of the Stratosphere, from approximately 15 to 35 kilometers above Earth.
Step 2: The stratosphere is characterized by an increase in temperature with height due to absorption of UV radiation by ozone.
Conclusion: Option B is correct.
Question 04CGL Pattern
On which date does the Summer Solstice occur in the Northern Hemisphere, resulting in the longest day of the year?
A) March 21
B) June 21
C) September 23
D) December 22
Correct answer: B) June 21
Step-by-step Solution
Step 1: A solstice occurs twice a year when the Sun reaches its highest or lowest point relative to the celestial equator.
Step 2: On June 21, the Northern Hemisphere is tilted closest to the sun, making it the Summer Solstice in the north.
Step 3: This results in the maximum duration of daylight in the Northern Hemisphere.
Conclusion: Option B is correct.
Question 05CGL Pattern
Which local wind is warm, dry, blows down the eastern slopes of the Rocky Mountains, and is famously known as the 'Snow Eater'?
A) Chinook
B) Loo
C) Mistral
D) Harmattan
Correct answer: A) Chinook
Step-by-step Solution
Step 1: Chinook is a Foehn-type wind in North America.
Step 2: As it descends the eastern slopes of the Rockies, it compresses and warms up adiabatically, rapidly raising temperatures.
Step 3: This rapid warming causes snow to melt and sublimate quickly, giving it the nickname 'Snow Eater'.
Conclusion: Option A is correct.
Question 06CGL Pattern
Which type of rock is formed by the alteration of pre-existing rocks under the influence of high temperature and pressure without melting?
A) Igneous Rock
B) Sedimentary Rock
C) Metamorphic Rock
D) Volcanic Rock
Correct answer: C) Metamorphic Rock
Step-by-step Solution
Step 1: Rocks that undergo physical or chemical changes due to intense heat, pressure, or chemically active fluids are classified as metamorphic rocks.
Step 2: Igneous rocks form from cooling magma, and sedimentary rocks form from compacted sediments.
Conclusion: Option C is correct.
Question 07CGL Pattern
The semi-fluid, ductile layer in the upper mantle on which tectonic plates float is known as the:
A) Lithosphere
B) Asthenosphere
C) Barysphere
D) Hydrosphere
Correct answer: B) Asthenosphere
Step-by-step Solution
Step 1: The mechanical classification of Earth's layers includes the lithosphere (rigid outer shell) and asthenosphere.
Step 2: The asthenosphere is the highly viscous, mechanically weak, and ductile region of the upper mantle, lying below the lithosphere.
Step 3: It is the zone where partial melting occurs, supplying magma for volcanoes.
Conclusion: Option B is correct.
Question 08CGL Pattern
Which of the following gases is the third most abundant gas by volume in the Earth's atmosphere?
A) Carbon Dioxide
B) Argon
C) Hydrogen
D) Neon
Correct answer: B) Argon
Step-by-step Solution
Step 1: Analyze the gas composition of the atmosphere: Nitrogen (approx. 78.08%), Oxygen (approx. 20.95%).
Step 2: The third most abundant gas is Argon, which makes up about 0.93% of the atmosphere.
Step 3: Carbon Dioxide is fourth at about 0.04%.
Conclusion: Option B is correct.
Question 09CGL Pattern
What is the name of the planetary wind system that blows from the Subtropical High Pressure belts to the Equatorial Low Pressure belt?
A) Westerlies
B) Polar Easterlies
C) Trade Winds
D) Monsoon Winds
Correct answer: C) Trade Winds
Step-by-step Solution
Step 1: Winds blow from high pressure areas to low pressure areas.
Step 2: The winds blowing from the Subtropical Highs (horse latitudes) to the Equatorial Low (doldrums) are the Trade Winds.
Step 3: They blow from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere.
Conclusion: Option C is correct.
Question 10CGL Pattern
The point on the Earth's surface directly above the focus (hypocentre) of an earthquake is known as the:
A) Epicentre
B) Seismic Node
C) Core Point
D) Fault Line
Correct answer: A) Epicentre
Step-by-step Solution
Step 1: The place inside the Earth where the earthquake rupture starts is called the focus or hypocentre.
Step 2: The point on the Earth's surface vertically directly above the focus is the epicentre.
Step 3: Seismic waves travel outward from the epicentre, causing maximum damage near it.
Conclusion: Option A is correct.
Question 11CGL Pattern
Which planet is known as the 'Morning Star' and 'Evening Star', and rotates clockwise (from East to West) on its axis?
A) Mercury
B) Venus
C) Mars
D) Uranus
Correct answer: B) Venus
Step-by-step Solution
Step 1: Venus is visible in the east before sunrise and in the west after sunset, earning its morning/evening star nickname.
Step 2: Unlike most planets, Venus exhibits retrograde (clockwise) rotation.
Conclusion: Option B is correct.
Question 12CGL Pattern
Marble is a metamorphic rock that originates from the metamorphism of which sedimentary rock?
A) Sandstone
B) Limestone
C) Shale
D) Granite
Correct answer: B) Limestone
Step-by-step Solution
Step 1: Under high temperature and pressure, sedimentary rocks recrystallize.
Step 2: Limestone, which is made of calcium carbonate, transforms into Marble.
Step 3: Sandstone transforms into Quartzite, and Shale transforms into Slate.
Conclusion: Option B is correct.
Question 13CGL Pattern
Which atmospheric layer is the coldest, with temperatures dropping as low as -100°C, and is the layer where meteors burn up?
A) Stratosphere
B) Mesosphere
C) Thermosphere
D) Exosphere
Correct answer: B) Mesosphere
Step-by-step Solution
Step 1: Temperature decreases in the Troposphere, increases in the Stratosphere, and decreases again in the Mesosphere.
Step 2: The Mesosphere is the coldest atmospheric layer.
Step 3: It is also where most meteors vaporize (burn up) due to friction with air molecules.
Conclusion: Option B is correct.
Question 14CGL Pattern
The Gutenberg discontinuity forms the boundary separating which two major divisions of the Earth?
A) Crust and Mantle
B) Mantle and Core
C) Outer Core and Inner Core
D) Lithosphere and Asthenosphere
Correct answer: B) Mantle and Core
Step-by-step Solution
Step 1: Recall the boundary discontinuities. The Moho discontinuity separates crust and mantle.
Step 2: The Gutenberg discontinuity separates the Mantle from the Core at a depth of about 2,900 km.
Conclusion: Option B is correct.
Question 15CGL Pattern
The Coriolis Effect, which deflects winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, is caused by the Earth's:
A) Orbital Tilt
B) Revolution around the Sun
C) Rotation on its axis
D) Spherical Shape
Correct answer: C) Rotation on its axis
Step-by-step Solution
Step 1: The Coriolis effect is an inertial force.
Step 2: It is caused by the Earth's rotation. Because the Earth rotates, objects moving freely over its surface are deflected.
Step 3: This deflection is described by Ferrel's Law.
Conclusion: Option C is correct.
Question 16CGL Pattern
Which local wind blowing from the Sahara desert towards West Africa is known as 'The Doctor' because of its dry and cooling nature?
A) Loo
B) Harmattan
C) Sirocco
D) Mistral
Correct answer: B) Harmattan
Step-by-step Solution
Step 1: The Harmattan is a dry and dusty trade wind.
Step 2: It blows from the Sahara desert southwards over West Africa to the Gulf of Guinea between November and March.
Step 3: It relieves the humid tropical dampness, providing refreshing dry air, hence its nickname 'The Doctor'.
Conclusion: Option B is correct.
Question 17CGL Pattern
Which seismic wave can travel through both solid and liquid mediums, and is longitudinal in nature?
A) S-waves
B) P-waves
C) L-waves
D) Rayleigh waves
Correct answer: B) P-waves
Step-by-step Solution
Step 1: Primary (P) waves are compressional or longitudinal waves.
Step 2: Because they are compressional, they can travel through solid, liquid, and gaseous materials.
Step 3: Secondary (S) waves are shear/transverse waves and cannot travel through liquid (the liquid outer core blocks them).
Conclusion: Option B is correct.
Question 18CGL Pattern
The term 'Sial' representing the continental crust is chemically composed of which two primary elements?
A) Silicon and Aluminium
B) Silicon and Magnesium
C) Silicon and Iron
D) Sodium and Aluminium
Correct answer: A) Silicon and Aluminium
Step-by-step Solution
Step 1: SIAL is a combination of 'Si' (Silica/Silicon) and 'Al' (Aluminium).
Step 2: It refers to the upper layer of the Earth's crust, which forms the continents and is rich in silica and alumina.
Conclusion: Option A is correct.
Question 19CGL Pattern
The phenomenon of 'Aphelion' refers to the position of the Earth when it is:
A) Closest to the Sun
B) Farthest from the Sun
C) Closest to the Moon
D) Directly under the Solar Equator
Correct answer: B) Farthest from the Sun
Step-by-step Solution
Step 1: The Earth orbits the sun in an ellipse, meaning the distance varies.
Step 2: Perihelion (from Greek 'peri' meaning near) is the closest point, occurring in January.
Step 3: Aphelion (from Greek 'apo' meaning away) is the farthest point, occurring in July.
Conclusion: Option B is correct.
Question 20CGL Pattern
Which of the following is a classic example of an extrusive igneous rock, formed by rapid cooling of lava on the surface, which is rich in basaltic minerals?
A) Granite
B) Basalt
C) Gneiss
D) Sandstone
Correct answer: B) Basalt
Step-by-step Solution
Step 1: Extrusive igneous rocks form when magma reaches the surface as lava and cools rapidly.
Step 2: Basalt is a fine-grained, dark extrusive igneous rock that forms oceanic crust and volcanic plains.
Step 3: Granite is intrusive (cools slowly underground, coarse-grained).
Conclusion: Option B is correct.
Strategy errors to avoid
!
Conflating Discontinuities
Do not mix up Mohorovicic (Moho) and Gutenberg discontinuities. Moho separates the outer crust from the mantle, whereas Gutenberg divides the mantle from the deep core. Remembering them in order from outer to inner is crucial.
!
Wind Directions & Characteristics
Always associate Chinook with the USA/Canada Rocky Mountains and Harmattan with West Africa. CGL questions often pair these local winds with incorrect geographic regions to trip up candidates.