The Earth

1. Consider the following statements regarding the rotation of the Earth

Consider the following statements regarding the rotation of the Earth :

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  • 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 ?

1 only
3 and 4 only
1, 3 and 4
2, 3 and 4
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UPSC CAPF – 2024
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Statements 1, 3, and 4 are correct. Statement 2 is incorrect.
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 date to go back a day, while crossing from east to west causes the date to advance a day.
Standard time zones are nominally 15 degrees wide, corresponding to one hour difference, although political boundaries often cause deviations. The International Date Line is located roughly along the 180° longitude. The synchronous rotation of the Moon (rotating and revolving at the same rate and direction) is why the same side of the Moon always faces Earth.

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

Which one among the following statements is not correct?

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The plane of separation between the crust and mantle is known as Mohorovicic discontinuity
The mantle contains more than two-third of the total material mass of the Earth
The mantle is composed of the heaviest materials of the Earth
The inner core of the Earth is in solid state
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UPSC CAPF – 2012
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Statement C is incorrect. The mantle is not composed of the heaviest materials of the Earth. The inner and outer core are composed of the heaviest materials, primarily iron and nickel. The density increases from the crust through the mantle to the core.
Understanding the composition and characteristics of Earth’s interior layers (crust, mantle, core) is crucial for answering questions about geophysics.
Statement A is correct: The Mohorovicic discontinuity (Moho) is the boundary between the Earth’s crust and the mantle. Statement B is correct: The mantle constitutes about 84% of Earth’s volume and around 67% of its mass. Statement D is correct: Due to immense pressure, the inner core is in a solid state despite extremely high temperatures.

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

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

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The Earth’s rotation causes the Earth to bulge slightly at the equator and flatten at the poles
The Earth’s rotation causes the Earth to bulge slightly at the poles and flatten at the equator
The Earth’s revolution causes the Earth to bulge slightly at the equator and flatten at the poles
The Earth’s revolution causes the Earth to bulge slightly at the poles and flatten at the equator
This question was previously asked in
UPSC CAPF – 2012
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The Earth is not a perfect sphere but takes the shape of an oblate ellipsoid (or oblate spheroid), which means it is slightly flattened at the poles and bulges at the equator. This shape is a result of the Earth’s rotation. The centrifugal force generated by rotation is greatest at the equator because the linear velocity is highest there. This outward force counteracts gravity more effectively at the equator, causing the material there to bulge outwards, while the poles, experiencing minimal centrifugal force, are slightly flattened.
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.
The difference between the equatorial diameter and the polar diameter is about 43 kilometers (approximately 12,756 km vs 12,714 km). This difference is relatively small compared to the overall size of the Earth, but it is significant enough for accurate measurements and understanding of Earth’s gravity field.

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4. Statement I : The Earth is shaped more like a tangerine. Statement II

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

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Both the statements are individually true and statement II is the correct explanation of statement I
Both the statements are individually true but statement II is not the correct explanation of statement I
Statement I is true but statement II is false
Statement I is false but statement II is true
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UPSC CAPF – 2011
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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.
Statement I is true; the Earth is not a perfect sphere but is slightly flattened at the poles and bulges at the equator due to centrifugal force from its rotation, a shape often approximated by calling it an oblate spheroid or using the analogy of a tangerine or orange. Statement II is false; the Earth spins at a constant *angular* velocity (completing one rotation in roughly 24 hours), but the *linear* velocity (speed along the surface) is highest at the equator because points on the equator are farthest from the axis of rotation. The linear velocity decreases towards the poles and is essentially zero at the geographical poles which lie on the axis of rotation.

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5. Which of the following statements is/are correct? 1. The Earth’s cru

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.

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1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC NDA-2 – 2022
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Let’s analyze each statement:
1. The Earth’s crust is brittle in nature: This statement is correct. The upper part of the Earth’s crust behaves in a brittle manner, meaning it tends to break and fracture under stress rather than deform plastically. This brittle behavior is responsible for phenomena like faulting and earthquakes.
2. The mean thickness of the oceanic crust is 15 km whereas that of the continental crust is around 30 km: This statement is incorrect. The oceanic crust is significantly thinner than the continental crust. The mean thickness of the oceanic crust is typically around 5-10 km, while the mean thickness of the continental crust is around 30-40 km (and can be up to 70 km under major mountain ranges).
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.
The oceanic crust is primarily composed of basalt and gabbro and is denser than the continental crust, which is mainly composed of granitic and andesitic rocks. This difference in density and thickness is fundamental to plate tectonics and the formation of Earth’s surface features.

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

Which one of the following best describes the Lithosphere ?

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Upper and lower mantle
Crust and core
Crust and upper mantle
Lower mantle and core
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UPSC NDA-2 – 2021
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The correct option is 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.
Beneath the lithosphere lies the Asthenosphere, which is a mechanically weak, ductile layer of the upper mantle. The lithosphere essentially rides on the asthenosphere. Option A is incorrect as it omits the crust. Option B is incorrect as it includes the core but omits a large part of the mantle. Option D describes deeper layers below the lithosphere.

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7. According to the Geo-scientists, the shape of the earth is: 1. round 2

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:

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2, 3 and 4
1, 2 and 3
1 and 2 only
3 and 4 only
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UPSC NDA-2 – 2015
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The correct answer is D) 3 and 4 only. According to geoscientists, the Earth’s shape is most accurately described as an oblate ellipsoid (or oblate spheroid), meaning it is flattened at the poles and bulges at the equator due to its rotation. While it is also approximately spherical or close to that of a sphere, “oblate ellipsoid” is the precise geodetic term for its overall shape. “Close to that of a sphere” is also accurate as it acknowledges the deviation from a perfect sphere while still capturing the general shape. “Round” and “spherical” are less precise terms used in common language.
Geoscientists use precise terms like ‘oblate ellipsoid’ to describe the Earth’s shape, which deviates from a perfect sphere.
The Earth’s equatorial diameter is about 43 km larger than its polar diameter. This slight bulge makes ‘oblate ellipsoid’ the most accurate geometric model. Saying it’s “close to that of a sphere” is also factually correct, as the deviation is relatively small compared to the overall size. Therefore, options 3 and 4 represent the descriptions used by geoscientists, with 4 being the most specific geometrical model.

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8. In a group discussion on shape and size of the Earth, three students s

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?

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Student 1 only
Student 1 and Student 2 only
Student 2 and Student 3 only
Student 1, Student 2 and Student 3
This question was previously asked in
UPSC NDA-1 – 2022
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The correct answer is 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.
The Earth’s actual shape is even more irregular than an oblate spheroid due to variations in gravity and topography; this complex shape is called a geoid. However, for general purposes, an oblate spheroid is a good approximation. The difference between the equatorial and polar diameters is a consequence of the Earth’s formation and ongoing rotation.

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9. The maximum depth of Lithosphere is found in the

The maximum depth of Lithosphere is found in the

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Pacific Ocean.
Siberian Plain.
Patagonian Desert.
Himalayan Mountains.
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UPSC NDA-1 – 2021
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The lithosphere, which comprises the Earth’s crust and the rigid upper part of the mantle, varies greatly in thickness. It is generally thinnest under oceanic ridges (around 10 km) and thickest under stable continental interiors (cratons) and mountain belts formed by continental collision, where it can exceed 150-200 km.
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.
The Pacific Ocean is underlain by oceanic lithosphere, which is relatively thin compared to continental lithosphere. Siberian Plain and Patagonian Desert are continental regions, but the significant crustal root and thickened lithosphere associated with the collision forming the Himalayan mountains likely result in the maximum depth among the given options.

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

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

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Inner Core
Outer Core
Mantle
Crust
This question was previously asked in
UPSC Geoscientist – 2024
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The Earth’s layers, from outside to inside, are the Crust, Mantle, Outer Core, and Inner Core. The Crust is the outermost and thinnest layer.
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).
The thickness of the crust varies significantly; it is thinner under oceans (oceanic crust) and thicker under continents (continental crust). Despite this variation, it remains the thinnest layer compared to the mantle and core.

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