Convection currents, which move the tectonic plates, are found in which layer of the earth?
- A.Crust
- B.Mantle
- C.Outer core
- D.Inner core
Correct answer
Explanation
The correct answer is B, Mantle. Heat from the Earth's interior sets up slow convection currents in the mantle, and these drag the rigid plates resting on it.
Arthur Holmes proposed in the 1930s that hot mantle material rises, spreads sideways beneath the lithosphere, cools and sinks again, forming convection cells. The weak, partly molten upper layer of the mantle, the asthenosphere, lies just below the plates and lets them glide. Where currents rise, plates move apart at mid-ocean ridges; where they sink, plates are pulled down at subduction zones. The mantle extends from the base of the crust to about 2,900 km and holds most of the Earth's volume.
Why the others are wrong: A, the crust is the thin solid outer skin that forms the top of the plates, not where the driving currents flow. C, the outer core is liquid iron and nickel whose motion produces the Earth's magnetic field, not plate movement. D, the inner core is solid because of the enormous pressure.
Exam tip: mantle convection (Arthur Holmes) drives plates; outer core motion drives the magnetic field.
Practice Questions
View allWhich one among the following is the northernmost geographical location ?
- A.New Delhi
- B.Kathmandu
- C.Thimphu
- D.Dhaka
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New Delhi lies at about 28.6° N, a little north of both Kathmandu and Thimphu, even though Nepal and Bhutan lie to the north of most of India.
Read the full explanation →Which of the following is/are the applied forces in mechanical weathering process? 1. Gravitational force 2. Expansion force 3. Force due to water pressure Select the answer using the code given below :
- A.1 only
- B.1 and 2 only
- C.2 and 3 only
- D.1, 2 and 3
Show answer
Mechanical (physical) weathering breaks rocks without changing their chemistry, and all three forces drive it. Gravitational forces act as overburden pressure, load and shearing stress on rocks.
Read the full explanation →According to the Census 2011, the density of population in which one among the following States is the lowest ?
- A.Sikkim
- B.Nagaland
- C.Manipur
- D.Mizoram
Show answer
Census 2011 recorded about 52 persons per sq km in Mizoram, the lowest of the four states given. Mizoram is a hilly, heavily forested state with a small population of about 11 lakh, which keeps its density low.
Read the full explanation →Consider the following statements : 1. The Earth's magnetic field has reversed every few hundred thousand years. 2. When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide. 3. When living organisms originated, they modified the early atmosphere of the Earth. Which of the statements given above is/are correct ?
- A.1 only
- B.2 and 3 only
- C.1 and 3 only
- D.1, 2 and 3
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The magnetic field has flipped many times and life changed the early air, but the young Earth had almost no free oxygen.
Read the full explanation →With reference to the current trends in the cultivation of sugarcane in India, consider the following statements : 1. A substantial saving in seed material is made when 'bud chip settlings' are raised in a nursery and transplanted in the main field. 2. When direct planting of setts is done, the germination percentage is better with single-budded setts as compared to setts with many buds. 3. If bad weather conditions prevail when setts are directly planted, single-budded setts have better survival as compared to large setts. 4. Sugarcane can be cultivated using settlings prepared from tissue culture. Which of the statements given above is/are correct?
- A.1 and 2 only
- B.3 only
- C.1 and 4 only
- D.2, 3 and 4 only
Show answer
Bud chip nurseries save seed cane and tissue-culture settlings are used, but single-bud setts do worse than larger setts when planted directly.
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