The Earth

The Earth is part of World and Physical Geography. Below are notes on 9 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Distribution of Continents and Oceans

• Continental Drift Theory (CDT): Proposed by Alfred Wegener in 1912.
• CDT Core Idea: All continents formed a single supercontinent called Pangaea (meaning "all earth") surrounded by a mega-ocean called Panthalassa (meaning "all water").
• Pangaea Breakup: Pangaea began to split around 200 million years ago into Laurasia (northern continents) and Gondwanaland (southern continents), which further broke into present-day continents.
• Evidence for CDT:
• Jigsaw Fit: Remarkable matching of coastlines (e.g., South America and Africa).
• Rocks of Same Age: Presence of similar geological structures and rock formations across oceans (e.g., Appalachian Mountains of North America and Caledonian Mountains of Europe).
• Tillite Deposits: Widespread glacial deposits (tillites) indicating ancient glaciations across different continents (India, Africa, Australia, Antarctica), suggesting a common landmass.
• Placer Deposits: Gold placers on the Ghana coast, without source rock in Africa, but found in Brazil, implying their shared origin.
• Fossil Distribution: Identical plant (e.g., Glossopteris) and animal (e.g., Mesosaurus) fossils found on widely separated continents.
• Wegener's Forces: Wegener incorrectly attributed the drift to tidal forces and pole-fleeing force.
• Seafloor Spreading: Proposed by Harry Hess (1961); new oceanic crust is formed at midoceanic ridges and destroyed at oceanic trenches.
• Plate Tectonics Theory: Describes the largescale motions of Earth's lithosphere.
• Lithospheric Plates: Earth's lithosphere is divided into several major and minor rigid plates that float and move over the semi-fluid asthenosphere.
• Driving Force: Convection currents in the mantle are the primary driving force for plate movement.
• Types of Plate Boundaries:
• Divergent Boundaries: Plates move apart (constructive), forming midoceanic ridges, rift valleys (e.g., MidAtlantic Ridge, East African Rift).
• Convergent Boundaries: Plates move towards each other (destructive), leading to subduction, mountain building, trenches, and volcanoes (e.g., Himalayas, Andes, Mariana Trench).
• Transform Boundaries: Plates slide past each other horizontally (conservative), causing earthquakes (e.g., San Andreas Fault).

Earth's Movements: Rotation, Revolution, their effects

• Earth's Rotation: Movement of Earth on its own axis.
• Rotation Direction: West to East.
• Rotation Time (Sidereal Day): Approximately 23 hours 56 minutes 4.09 seconds.
• Effects of Rotation:
• Occurrence of day and night.
• Generation of the Coriolis force, causing deflection of winds and ocean currents.
• Apparent daily movement of the Sun, Moon, and stars.
• Rotation Speed: Maximum at the Equator, decreases towards the poles, and is zero at the Poles.
• Earth's Revolution: Movement of Earth around the Sun in an elliptical orbit.
• Revolution Time: Approximately 365.25 days (one year).
• Effects of Revolution:
• Change of seasons.
• Variation in the length of day and night.
• Shifting of global wind belts.
• Perihelion: Point in Earth's orbit where it is nearest to the Sun (~147 million km). Generally occurs around January 3.
• Aphelion: Point in Earth's orbit where it is farthest from the Sun (~152 million km). Generally occurs around July 4.

Geological Time Scale

• Paleozoic Era:
• Cambrian Period: Origin of shelled animals.
• Devonian Period: First insects.
• Carboniferous Period: First reptiles.
• Mesozoic Era (Age of Reptiles): Dinosaurs present throughout.
• Triassic Period: First dinosaurs, first mammals.
• Jurassic Period: Dominance of dinosaurs, first birds.
• Cretaceous Period: Dinosaurs peaked; Mass extinction of dinosaurs (K-Pg event) occurred at period end.
• Cenozoic Era (Age of Mammals):
• Eocene Epoch: Primitive mammals diversified; Not the origin of modern man.
• Pleistocene Epoch: Emergence of early humans.
• Holocene Epoch: Modern man (Homo sapiens).

Interior of the Earth: Crust, Mantle, Core

• Earth's average density: 5.5 gm/cm³.
• Temperature increases approximately 1°C for every 32 meters of depth in the Earth's interior.
• Overall Earth's composition: Iron is the most abundant natural element.
• Crust:
• Thinnest layer of the Earth.
• Brittle in nature.
• Continental crust: ~30-70 km thick (average ~30-40 km).
• Oceanic crust: ~5-10 km thick (average ~7 km).
• Major elemental composition: Silica (Si), Aluminium (Al), Magnesium (Mg).
• Carbon content: Approximately 0.025%.
• The maximum thickness of the Lithosphere (which includes the crust) is found under continental mountain ranges like the Himalayas.
• Mantle:
• Located between the crust and the core.
• Comprises over two-thirds (approx. 84%) of the Earth's total volume and mass.
• Composed of dense silicate rocks rich in iron and magnesium.
• Core:
• Composed of the heaviest materials of the Earth, primarily Iron (Fe) and Nickel (Ni) (NIFE).
• Outer Core: Liquid state.
• Inner Core: Solid state.
• The inner core remains solid despite intense heat due to the immense pressure exerted on it, which raises its melting point significantly.
• Lithosphere:
• Comprises the Earth's crust and the uppermost solid part of the mantle.
• Discontinuities:
• Mohorovicic Discontinuity (Moho): Separates the crust from the mantle.
• Sequence of layers from Earth's center to surface: Inner Core → Outer Core → Mantle → Crust.

Latitudes and Longitudes: Graticule system, important lines

• Latitudes: Imaginary circles parallel to the Equator, measuring angular distance North or South from 0° (Equator) to 90° (Poles).
• Key Latitudes:
• Equator (0°): Divides Earth into Northern & Southern Hemispheres.
• Tropic of Cancer (23.5° N).
• Tropic of Capricorn (23.5° S).
• Arctic Circle (66.5° N).
• Antarctic Circle (66.5° S).
• Longitudes: Imaginary semicircles connecting North & South Poles, measuring angular distance East or West from 0° (Prime Meridian) to 180°.
• Key Longitudes:
• Prime Meridian (0°): Passes through Greenwich, UK; reference for global time zones.
• International Date Line (180° Longitude): Roughly follows 180° meridian, marks where a new calendar day begins.
• Graticule System: The grid network formed by the intersection of parallels of latitude and meridians of longitude, enabling precise location of any point on Earth's surface.
• Parsec (pc): Unit of astronomical distance. Defined as the distance at which one Astronomical Unit (AU) subtends an angle of one arcsecond.
• Astronomical Unit (AU): Represents the average distance from the Earth to the Sun.

Origin and Evolution of the Earth

• W.M. Davis proposed the concept of the Normal Cycle of Erosion.
• Dynamic changes on Earth's surface are influenced by electromagnetic radiation, geothermal energy, gravitational force, plate movements, Earth's rotation, and Earth's revolution.
• Natural disaster categories: Blizzards (Atmospheric), Soil erosion (Terrestrial), Tsunami (Aquatic), Locusts (Biological).
• The average temperature of the Earth is 15°C.
• Earth is the only known planet to harbor life, largely attributed to its atmosphere containing a crucial mixture of oxygen, nitrogen, and carbon dioxide.

Seasons, Solstices, and Equinoxes

• Earth's orbit around the Sun is elliptical.
• Perihelion: Earth is closest to the Sun (approx. 147 million km). Occurs around January 3.
• Aphelion: Earth is farthest from the Sun (approx. 152 million km). Occurs around July 4.
• Seasons: Primarily caused by Earth's axial tilt (23.5 degrees) relative to its orbital plane and its revolution around the Sun.
• Axial Parallelism: Earth's axis maintains its tilt in the same direction throughout its orbit.
• Summer Solstice (Northern Hemisphere): Around June 21/22. Northern Hemisphere tilted towards Sun. Sun's rays vertical over Tropic of Cancer (23.5° N). Longest day in NH, shortest day in Southern Hemisphere (SH).
• Winter Solstice (Northern Hemisphere): Around December 21/22. Northern Hemisphere tilted away from Sun. Sun's rays vertical over Tropic of Capricorn (23.5° S). Shortest day in NH, longest day in SH.
• Vernal/Spring Equinox: Around March 20/21. Sun's rays vertical over the Equator. Equal day and night globally.
• Autumnal Equinox: Around September 22/23. Sun's rays vertical over the Equator. Equal day and night globally.

Shape of the Earth: Geoid, Oblate Spheroid, Gravity

• Earth's shape is an oblate spheroid (or oblate ellipsoid), meaning it is flattened at the poles and bulges at the equator.
• This oblate spheroid shape is primarily caused by Earth's rotation, which generates centrifugal force.
• As a consequence, the equatorial diameter is greater than the polar diameter.
• Earth's rotation speed is highest at the equator and lowest at the poles.
• The equatorial circumference of the Earth is approximately 40,000 km.
• The total surface area of Earth is approximately 510 million square kilometres.
• The mean elevation of land surface on Earth is approximately 840 metres.
• Viewed from space, the Earth looks predominantly blue due to the presence of vast water bodies.
• Earth is often broadly described as "round," "spherical," or "close to that of a sphere."

Time Zones: Standard Time, International Date Line

• Earth rotates 360° in approximately 24 hours, leading to a longitudinal time difference of 15° per hour (360° / 24 hours = 15°/hour).
• Time Zones are geographic regions that observe a uniform standard time, typically differing by one hour for every 15° of longitude.
• Standard Time is the uniform time adopted over a country or a large region by referring to a specific standard meridian to avoid local time variations.
• Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC) is the reference time standard at the Prime Meridian (0° longitude), serving as the basis for all other time zones.
• The International Date Line (IDL) is an imaginary line, mostly following the 180° longitude meridian through the Pacific Ocean, where the date changes.

8. The Mars

Practice MCQs: The Earth

Earth's Movements: Rotation, Revolution, their effects

1. An effective Coriolis force results from

   Asked in: BPSC Prelims Exam 67th Cancelled

   1. solar system
   2. earth rotation
   3. interior of the earth
   4. Colorado and Gulf Streams
   Show answer

   Answer: B. earth rotation

   The Coriolis force deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The magnitude of the force depends on the object's velocity, the Earth's rotation rate, and the latitude.

2. Which of the following statements is / are correct ? 1. The earth is nearest to the Sun at Perihelion, which generally occurs on January 3 2. The earth is farthest away from the Sun at Perihelion, which generally occurs on July 4 3. The earth is farthest away from the Sun at Aphelion, which generally occurs on July 4 4. The earth is nearest to the Sun at Aphelion, which generally occurs on January 3 Select the correct answer using the code given below :

   Asked in: UPSC CDS 1 2016

   1. 1 only
   2. 2 and 4
   3. 1 and 3
   4. 1 and 2
   Show answer

   Answer: C. 1 and 3

   - Perihelion is the point in the Earth's orbit where it is nearest to the Sun. This generally occurs around January 3rd each year. - Aphelion is the point in the Earth's orbit where it is farthest from the Sun. This generally occurs around July 4th each year. - The slight eccentricity of the Earth's orbit causes this variation in distance, although it is not the primary reason for the seasons (axial tilt is).

3. Which of the following statements is true regarding earth movement ? 1. Earth rotates on its axis from west to east resulting into seasonal changes. 2. Earth revolution around sun results into occurrence of day and night on earth.

   Asked in: JPSC CS Prelims 2021

   1. Only 1 is true.
   2. Both 1 and 2 are true.
   3. Only 2 is true.
   4. Both 1 and 2 are false.
   Show answer

   Answer: D. Both 1 and 2 are false.

   Rotation is movement on an axis, causing cycles like day and night. Revolution is movement around another body, causing cycles like seasons (due to axis tilt).

4. Which one of the following statements is correct ?

   Asked in: MPSC CS Prelims 2016

   1. The Earth rotates from East to West.
   2. The Earth rotates from West to East.
   3. The Earth rotates from South to North.
   4. The Earth rotates from North to South.
   Show answer

   Answer: B. The Earth rotates from West to East.

   The Earth rotates on its axis from west to east. This rotation is why the sun, moon, and stars appear to rise in the east and set in the west.

5. The speed of rotation of the earth is least A) along the Equator B) at the North-Pole C) along the Tropic of Cancer D) along the Arctic Circle

   Asked in: ASSISTANT AUDIT OFFICER 2017 18 2017

   1. along the Equator
   2. at the North-Pole
   3. along the Tropic of Cancer
   4. along the Arctic Circle
   Show answer

   Answer: B. at the North-Pole

   The speed of Earth's rotation varies with latitude, being fastest at the equator and slowest at the poles.

6. The significance of 23 hr 56 min 4.09 sec is

   Asked in: ASSISTANT ENGINEER(ELECTRICAL) 2016 · TOURIST INFORMATION OFFICER(TIO) 2017

   1. the exact time taken by our moon to make one revolution around earth
   2. the biological cycle clock of Human body
   3. the precise time taken by earth for one rotation
   4. none of the above
   Show answer

   Answer: C. the precise time taken by earth for one rotation

   23 hours 56 minutes 4.09 seconds is the duration of one sidereal rotation of the Earth.

7. The significance of 23 hr 56 min 4.09 sec is the exact time taken by our moon to

   Asked in: ASSISTANT ENGINEER(ELECTRICAL) 2016

   1. make one revolution around earth
   2. the biological cycle clock of Human body
   3. the precise time taken by earth for one rotation
   4. none of the above
   Show answer

   Answer: C. the precise time taken by earth for one rotation

   The question tests knowledge of astronomical and geophysical time periods. The sidereal day is distinct from the solar day (24 hours), which is the time it takes for the Sun to appear in the same position in the sky.

Interior of the Earth: Crust, Mantle, Core

8. What is the approximate percentage of carbon in the Earth's crust ?

   Asked in: UPSC CDS 2 2021

   1. 0.045%
   2. 0.025%
   3. 0.015%
   4. 0.005%
   Show answer

   Answer: B. 0.025%

   - The Earth's crust is dominated by silicates. - Carbon in the crust is mainly found in carbonates and organic matter. - Its percentage by weight is relatively low compared to the major rock-forming elements.

9. Which one of the following is the thinnest layer of the Earth ?

   Asked in: UPSC Geoscientist 2024

   1. Inner Core
   2. Outer Core
   3. Mantle
   4. Crust
   Show answer

   Answer: D. Crust

   The relative thicknesses of Earth's main layers are: Crust (5-70 km), Mantle (~2900 km), Outer Core (~2300 km), and Inner Core (~1220 km).

10. Despite intense heat in the core of the Earth, how can its central part can stay in solid form ?

    Asked in: GPSC Prelims CSP 2 2017

    1. Due to the intense pressure on the central part, its boiling point is high
    2. Due to the low pressure on the central part, its boiling point is high
    3. Due to the intense pressure on the central part, its boiling point is low
    4. Due to the low pressure on the central part, its boiling point is low
    Show answer

    Answer: A. Due to the intense pressure on the central part, its boiling point is high

    The inner core of the Earth is composed primarily of iron and nickel and is extremely hot (estimated to be between 5,200°C and 6,000°C). While this temperature is well above the melting point of these metals at standard atmospheric pressure, the immense pressure at the Earth's core (estimated to be millions of times atmospheric pressure) significantly raises their melting point. At this extreme pressure, the material remains solid despite the high temperature.

11. What is the average density of the earth as a whole ?

    Asked in: GPSC Prelims CSP 2 2017

    1. 2.7 gm/cm³
    2. 3.0 gm/cm³
    3. 5.5 gm/cm³
    4. 16.0 gm/ cm³
    Show answer

    Answer: C. 5.5 gm/cm³

    The Earth is layered, with the crust being less dense (~10-13 gm/cm³) due to composition (iron-nickel) and pressure. The average density of the entire Earth, considering the mass and volume of all layers, is calculated to be around 5.5 gm/cm³.

12. Which one of the following natural elements of the earth as whole is found in highest percentage?

    Asked in: GPSC Prelims CSP 2 2019

    1. Nickel
    2. Magnesium
    3. Iron
    4. Aluminium
    Show answer

    Answer: C. Iron

    When considering the Earth as a whole (crust, mantle, and core), Iron (Fe) is the most abundant element by mass, primarily concentrated in the Earth's core.

13. What is the average increase of temperature with increasing depth in the interior of the earth?

    Asked in: MPSC CS Prelims 2015

    1. 1°C for every 32 metres
    2. 1°C for every 64 metres
    3. 1°C for every 40 metres
    4. 1°C for every 80 metres
    Show answer

    Answer: A. 1°C for every 32 metres

    The geothermal gradient is the rate of increasing temperature with respect to increasing depth within the Earth. It varies depending on geological location.

14. Examine the following statements and select the proper option. Statement ‘A’: Inner core of the Earth is made up by Nickel and Ferrous. Statement ‘B’: The Earth’s crust is made up of Silica, Aluminium and Magnesium.

    Asked in: MPSC CS Prelims 2019

    1. Statement ‘A’ and ‘B’ are both correct.
    2. Statement ‘A’ is correct and ‘B’ is wrong.
    3. Statement ‘A’ is wrong and ‘B’ is correct.
    4. Statement ‘A’ and ‘B’ are both wrong.
    Show answer

    Answer: A. Statement ‘A’ and ‘B’ are both correct.

    Statement A: The Earth's inner core is primarily composed of an alloy of iron (ferrous) and nickel, with trace amounts of other elements. This statement is correct. Statement B: The Earth's crust is primarily composed of silicate rocks. The major elements in the Earth's crust are Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, and Magnesium. While simplified, stating it is made up of Silica (Silicon and Oxygen compounds), Aluminium, and Magnesium reflects the major components of the continental crust (rich in Si and Al, often referred to as SiAl) and the oceanic crust (rich in Si and Mg, often referred to as SiMa). This statement is also considered correct in this general context.

15. The maximum depth of Lithosphere is found in the

    Asked in: UPSC NDA 1 2021

    1. Pacific Ocean.
    2. Siberian Plain.
    3. Patagonian Desert.
    4. Himalayan Mountains.
    Show answer

    Answer: D. Himalayan Mountains.

    Continental lithosphere is generally much thicker than oceanic lithosphere. Major mountain ranges formed by collision, like the Himalayas, involve significant thickening of the crust and the underlying lithospheric mantle, leading to greater overall lithospheric depth compared to oceanic areas, plains, or deserts.

16. Which one of the following best describes the Lithosphere ?

    Asked in: UPSC NDA 2 2021

    1. Upper and lower mantle
    2. Crust and core
    3. Crust and upper mantle
    4. Lower mantle and core
    Show answer

    Answer: C. Crust and upper mantle

    The Earth's structure is typically described in terms of layers: the crust, the mantle, and the core. These layers can be further divided based on physical properties (like rigidity) or chemical composition. The Lithosphere is defined as the rigid outer layer of the Earth. It consists of the entire crust (continental and oceanic) and the uppermost, rigid part of the mantle, often called the lithospheric mantle.

17. Which of the following statements is/are correct? 1. The Earth's crust is brittle in nature. 2. The mean thickness of the oceanic crust is 15 km whereas that of the continental crust is around 30 km. Select the correct answer using the code given below.

    Asked in: UPSC NDA 2 2022

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Show answer

    Answer: A. 1 only

    The Earth's crust is the outermost solid shell of the planet and exhibits brittle characteristics, particularly near the surface. Oceanic and continental crusts differ significantly in their thickness and composition.

18. The sequence of geological composition from the depth to the surface of the Earth is : A) Crust $\rightarrow$ Mantle $\rightarrow$ Inner core $\rightarrow$ Outer core B) Mantle $ \rightarrow$ Crust $\rightarrow$ Inner core $ \rightarrow$ Outer core C) Outer core $\rightarrow$ Inner core $\rightarrow$ Crust $\rightarrow$ Mantle D) Inner core $\rightarrow$ Outer core $\rightarrow$ Mantle $\rightarrow$ Crust

    Asked in: TSPSC Group 1 Prelims 2023

    1. Crust $\rightarrow$ Mantle $\rightarrow$ Inner core $\rightarrow$ Outer core
    2. Mantle $\rightarrow$ Crust $\rightarrow$ Inner core $\rightarrow$ Outer core
    3. Outer core $\rightarrow$ Inner core $\rightar‐ row$ Crust $\rightarrow$ Mantle
    4. Inner core $\rightarrow$ Outer core $\rightar‐ row$ Mantle $\rightarrow$ Crust
    Show answer

    Answer: D. Inner core $\rightarrow$ Outer core $\rightar‐ row$ Mantle $\rightarrow$ Crust

    The Earth's internal structure is layered based on seismic studies and analysis of rock properties, with density and temperature generally increasing with depth.

19. Which one among the following statements is not correct?

    Asked in: UPSC CAPF 2012

    1. The plane of separation between the crust and mantle is known as Mohorovicic discontinuity
    2. The mantle contains more than two-third of the total material mass of the Earth
    3. The mantle is composed of the heaviest materials of the Earth
    4. The inner core of the Earth is in solid state
    Show answer

    Answer: C. The mantle is composed of the heaviest materials of the Earth

    Understanding the composition and characteristics of Earth's interior layers (crust, mantle, core) is crucial for answering questions about geophysics.

20. In the structure of the planet Earth, below the mantle, the core is mainly made up of which of the following?

    Asked in: GS 32 2023 IS DEEO 1505 2024

    1. Aluminium
    2. Silicon
    3. Iron
    4. Chromium
    Show answer

    Answer: C. Iron

    The Earth's structure consists of several layers: crust, mantle, outer core, and inner core. The mantle is primarily composed of silicate rocks, rich in iron and magnesium. Below the mantle lies the core, which is divided into the outer core and the inner core. Both parts of the core are predominantly composed of iron, with a significant amount of nickel. The outer core is liquid, while the inner core is solid.

Latitudes and Longitudes: Graticule system, important lines

21. The distance at which the average radius of Earth's orbit subtends an angle of 1 arc second, is known as :

    Asked in: RO ARO pre 2023

    1. 1 astronomical unit
    2. 1 light year
    3. 1 Parsec
    4. 1 Fermi
    Show answer

    Answer: C. 1 Parsec

    A parsec is a fundamental unit of astronomical distance derived from parallax measurements, where the 'sec' in parsec comes from arcsecond. One parsec is approximately 3.26 light-years or 206,265 astronomical units.

Origin and Evolution of the Earth

22. The concept of Normal Cycle of Erosion was given by :

    Asked in: HPPSC HPAS Prelims 2017

    1. Davis, W.M.
    2. Penck, W.
    3. Strahler, A.
    4. Thornbury, W.D.
    Show answer

    Answer: A. Davis, W.M.

    Davis's Cycle of Erosion describes the sequential changes in landforms through time (stages of youth, maturity, and old age) under the influence of denudation after an initial uplift.

23. Consider the following: Electromagnetic radiation 1. Geothermal energy 2. Gravitational force 3. Plate movements 4. Rotation of the earth 5. Revolution of the earth 6. Which of the above are responsible for bringing dynamic changes on the surface of the earth?

    Asked in: UPSC IAS 2013

    1. 1, 2, 3 and 4 only
    2. 1, 3, 5 and 6 only
    3. 2, 4, 5 and 6 only
    4. 1, 2, 3, 4, 5 and 6
    Show answer

    Answer: D. 1, 2, 3, 4, 5 and 6

    - Electromagnetic radiation (primarily from the Sun): Drives climate, weather systems, erosion (through wind, water, ice), photosynthesis (biological weathering), and thermal expansion/contraction (physical weathering). - Geothermal energy: Drives plate tectonics, volcanic activity, earthquakes, formation of mountains and ocean basins, and heat flow influencing subsurface processes. - Gravitational force: Causes mass movements (landslides, rockfalls), erosion by rivers (pulling water downhill), formation of tides (along with moon), and influences atmospheric circulation and ocean currents. - Plate movements: Directly responsible for earthquakes, volcanism, mountain building (orogeny), creation of rift valleys, and continental drift, constantly reshaping the Earth's crust. - Rotation of the earth: Causes Coriolis effect (influencing weather patterns, currents), contributes to tides (along with gravity), and diurnal temperature variations causing weathering. - Revolution of the earth: Along with axial tilt, causes seasons, influencing weather patterns, rates of weathering and erosion, formation and melting of ice/snow, and biological activity.

24. Match List-I with List-II and select the correct answer using the code given below the Lists : List-I (Natural disaster) List-II (Category)

    Asked in: UPSC CISF AC EXE 2024

    1. Blizzards 1. Terrestrial
    2. Soil erosion 2. Atmospheric
    3. Tsunami 3. Biological
    4. Locusts 4. Aquatic Code : A. A-3, B-4, C-1, D-2 B. A-3, B-1, C-4, D-2 C. A-2, B-1, C-4, D-3 D. A-2, B-4, C-1, D-3
    Show answer

    Answer: C. Tsunami 3. Biological

    Natural disasters can be broadly categorized based on their origin, such as atmospheric, terrestrial, aquatic, and biological.

25. The average temperature of the Earth due to the albedo effect is

    Asked in: WBCS Main Paper 4 2023

    1. 10°C
    2. 15°C
    3. 20°C
    4. 25°C
    Show answer

    Answer: B. 15°C

    The Earth's average temperature is a result of the balance between incoming solar radiation and outgoing thermal radiation, influenced by factors such as albedo (reflectivity) and the greenhouse effect. While albedo affects how much solar radiation is absorbed, the stated average temperature of 15°C is the actual observed average temperature of the Earth's surface under current conditions, which include the effect of greenhouse gases in the atmosphere. Without the natural greenhouse effect, the average temperature would be much lower, around -18°C.

Seasons, Solstices, and Equinoxes

26. The minimum distance between the sun and the earth occurs on

    Asked in: Inspector(Legal Metrology & Consumer Affairs) 2020

    1. [A] December 22
    2. [B] June 21
    3. [C] September 22
    4. [D] January 3
    Show answer

    Answer: D. [D] January 3

    This question relates to Earth's orbital mechanics and astronomical events. It tests knowledge about the Earth's elliptical orbit around the Sun and the points of closest and farthest approach.

Shape of the Earth: Geoid, Oblate Spheroid, Gravity

27. Choose the pair of words which have the same relationship as given by Round: Earth

    Asked in: GPSC Prelims CSP 1 2019

    1. Thin : Paper
    2. Height : Mountain
    3. Cube : Dice
    4. Wood : Table
    Show answer

    Answer: C. Cube : Dice

    The relationship between 'Round' and 'Earth' is that 'Round' describes the general shape of the 'Earth'. The Earth is approximately spherical, which can be described as round. This is a Shape:Object relationship, where the first word describes the shape of the second object. Let's analyze the options: A) Thin : Paper. 'Thin' is an adjective describing a property of 'Paper', but not its fundamental shape in the same way 'Round' describes 'Earth'. Paper comes in various forms (sheets, rolls, etc.) and can be thick or thin. B) Height : Mountain. 'Height' is a measurement associated with a 'Mountain', not its shape. Mountains have various shapes (conical, jagged, etc.), but 'Height' is a property, not a shape description. C) Cube : Dice. A standard 'Dice' is typically shaped like a 'Cube'. 'Cube' describes the specific shape of a 'Dice'. This fits the Shape:Object relationship closely, where the first word is the shape of the second object. D) Wood : Table. 'Wood' is the material from which a 'Table' is made. This is a Material:Object relationship, which is different from the Shape:Object relationship in the original pair. Option C provides the best analogy where the first term describes the shape of the second term, similar to 'Round' describing 'Earth'.

28. How many million square kilometres is the surface area of the earth ?

    Asked in: HAS Prelims 2019

    1. Approximately 550 million square kilometres
    2. Approximately 520 million square kilometres
    3. Approximately 510 million square kilometres
    4. Approximately 500 million square kilometers
    Show answer

    Answer: C. Approximately 510 million square kilometres

    - The Earth's total surface area is approximately 510.1 million square kilometers. - This area is composed of continents and islands (about 149 million sq km, or 29%) and oceans and seas (about 361 million sq km, or 71%). - Knowing the approximate dimensions of the Earth (radius, circumference, surface area, volume) is part of basic geographic knowledge.

29. In a group discussion on shape and size of the Earth, three students stated the following points : 1. Student 1 : The shape of the Earth is basically an oblate spheroid. 2. Student 2 : The polar diameter of the Earth is more than the equatorial diameter. 3. Student 3 : Bulge along the equatorial region is due to revolution of the Earth. Who among the above students is/are correct?

    Asked in: UPSC NDA 1 2022

    1. Student 1 only
    2. Student 1 and Student 2 only
    3. Student 2 and Student 3 only
    4. Student 1, Student 2 and Student 3
    Show answer

    Answer: A. Student 1 only

    Student 1: "The shape of the Earth is basically an oblate spheroid." This is correct. The Earth is not a perfect sphere; it is slightly flattened at the poles and bulges at the equator. An oblate spheroid is a geometric shape that accurately represents this form. Student 2: "The polar diameter of the Earth is more than the equatorial diameter." This is incorrect. The equatorial diameter (approx. 12,756 km) is greater than the polar diameter (approx. 12,714 km) by about 42 km, due to the equatorial bulge. Student 3: "Bulge along the equatorial region is due to revolution of the Earth." This is incorrect. The equatorial bulge is primarily caused by the Earth's rotation on its axis. The centrifugal force generated by rotation is strongest at the equator, leading to the outward bulge. Revolution refers to the Earth's orbit around the Sun. Therefore, only Student 1's statement is correct.

30. According to the Geo-scientists, the shape of the earth is: 1. round 2. spherical 3. close to that of a sphere 4. an oblate ellipsoid Select the correct answer using the code given below:

    Asked in: UPSC NDA 2 2015

    1. 2, 3 and 4
    2. 1, 2 and 3
    3. 1 and 2 only
    4. 3 and 4 only
    Show answer

    Answer: D. 3 and 4 only

    Geoscientists use precise terms like 'oblate ellipsoid' to describe the Earth's shape, which deviates from a perfect sphere.

31. The equatorial circumference of the Earth is nearly

    Asked in: UKPSC CS Prelims 2016

    1. 31,000 km
    2. 40,000 km
    3. 50,000 km
    4. 64,000 km
    Show answer

    Answer: B. 40,000 km

    The equatorial circumference is the distance around the Earth at the Equator.

32. Statement I : The Earth is shaped more like a tangerine. Statement II : The Earth spins faster at the Poles.

    Asked in: UPSC CAPF 2011

    1. Both the statements are individually true and statement II is the correct explanation of statement I
    2. Both the statements are individually true but statement II is not the correct explanation of statement I
    3. Statement I is true but statement II is false
    4. Statement I is false but statement II is true
    Show answer

    Answer: C. Statement I is true but statement II is false

    The Earth's shape is an oblate spheroid, and its rotation speed is greatest at the equator.

33. Why does the Earth assume the shape of an oblate ellipsoid?

    Asked in: UPSC CAPF 2012

    1. The Earth’s rotation causes the Earth to bulge slightly at the equator and flatten at the poles
    2. The Earth’s rotation causes the Earth to bulge slightly at the poles and flatten at the equator
    3. The Earth’s revolution causes the Earth to bulge slightly at the equator and flatten at the poles
    4. The Earth’s revolution causes the Earth to bulge slightly at the poles and flatten at the equat‐ or
    Show answer

    Answer: A. The Earth’s rotation causes the Earth to bulge slightly at the equator and flatten at the poles

    The Earth's oblate ellipsoid shape (bulging at the equator, flattened at the poles) is primarily caused by the centrifugal force resulting from its rotation.

34. What is the approximate value of mean elevation of land surface on earth ? (1) 1040 metre (3) 840 metre (2) 940 metre (4) 740 metre

    Asked in: Sr. Teacher Gr II (Sanskrit Edu.) Exam 2018 3 2018 · Sr. Teacher Gr II (Sanskrit Edu.) Exam 2018 4 2018

    1. 1040 metre
    2. 940 metre
    3. 840 metre
    4. 740 metre
    Show answer

    Answer: B. 940 metre

    This question tests general knowledge about the Earth's physical geography and geomorphology.

35. Viewed from the space, the earth looks mainly (a) Blue (b) Brown (c) Yellow (d) Red

    Asked in: ASSISTANT PROSECUTION OFFICER (PRELIM.) EXAM. 2018

    1. Blue
    2. Brown
    3. Yellow
    4. Red
    Show answer

    Answer: A. Blue

    The Earth appears blue from space due to the presence of large bodies of water (oceans).

Time Zones: Standard Time, International Date Line

36. If a ship sailing from Tokyo (Japan) on Sunday at 8 AM for San Francisco (USA) takes 8 hours to reach there. On which day it will reach there?

    Asked in: GPSC Prelims CSP 2 2019

    1. On Sunday
    2. On Saturday
    3. On Monday
    4. On Sunday midnight
    Show answer

    Answer: B. On Saturday

    Crossing the International Date Line from West to East requires subtracting a day.

37. Consider the following statements regarding the rotation of the Earth : Since the Earth rotates by 15° each hour, time zones normally differ by one hour At the International Date Line, the calendar day changes – advancing a day for eastward travel, dropping back a day for westward travel Daylight saving time advances the clock by one hour The Moon rotates and revolves about the Earth in the same direction that the Earth revolves around the Sun Which of the statements given above is/are correct ?

    Asked in: UPSC CAPF 2024

    1. 1 only
    2. 3 and 4 only
    3. 1, 3 and 4
    4. 2, 3 and 4
    Show answer

    Answer: C. 1, 3 and 4

    The Earth rotates approximately 15 degrees of longitude per hour, which is the basis for standard time zones. Daylight Saving Time involves advancing clocks, typically by one hour. The Moon orbits and rotates in the same direction as Earth orbits the Sun (counter-clockwise when viewed from above the North Pole). The International Date Line works such that crossing it from west to east causes the