The boundary that separates the crust from the mantle is known as the
- A.Conrad discontinuity
- B.Mohorovicic discontinuity
- C.Gutenberg discontinuity
- D.Lehmann discontinuity
Correct answer
Explanation
The correct answer is B, the Mohorovicic discontinuity. Named after the Croatian seismologist who noticed that earthquake waves suddenly speed up at a certain depth, it marks the base of the crust and the top of the mantle, and is commonly shortened to the Moho.
Option A, the Conrad discontinuity, lies inside the crust itself, between its lighter upper part and its denser lower part. Option C, the Gutenberg discontinuity, lies much deeper, at about 2,900 kilometres, and separates the mantle from the outer core; it is the usual distractor in this question. Option D, the Lehmann discontinuity, separates the liquid outer core from the solid inner core and is named after the Danish seismologist who identified the inner core. Revise the four names in order of depth, from Conrad to Lehmann, and the matching questions become easy marks.
Read the full article: Structure of the Earth and Rocks: Layers, Waves and Types
Practice Questions
View allWhich of the following seismic waves cannot travel through liquids?
- A.Primary or P waves
- B.Secondary or S waves
- C.Surface or L waves
- D.All three types
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They are transverse waves, in which particles vibrate at right angles to the direction of travel, and such motion cannot be sustained in a fluid, so S waves die out at the outer core.
Read the full explanation →Marble is a metamorphic rock formed from which of the following parent rocks?
- A.Sandstone
- B.Shale
- C.Limestone
- D.Granite
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Limestone is a sedimentary rock made largely of calcium carbonate, and when heat and pressure recrystallise it without melting it, the result is marble, the stone used in the Taj Mahal and in the Dilwara temples.
Read the full explanation →The Deccan Trap of peninsular India is composed mainly of which rock?
- A.Granite
- B.Basalt
- C.Limestone
- D.Gneiss
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The Deccan Trap was formed by vast fissure eruptions in which lava spread over the surface and cooled quickly, giving a fine-grained extrusive igneous rock, basalt.
Read the full explanation →Fossils of ancient plants and animals are found mainly in which type of rock?
- A.Igneous rocks
- B.Sedimentary rocks
- C.Metamorphic rocks
- D.Plutonic rocks
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They are built up layer by layer as sediment settles over the remains of living things and hardens gently, so shells, bones and plant matter survive as fossils.
Read the full explanation →Which element is the most abundant in the Earth crust by weight?
- A.Silicon
- B.Aluminium
- C.Oxygen
- D.Iron
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Almost half the weight of the crust, about 46.6 per cent, is oxygen, because it is locked into the silicate minerals of which nearly all crustal rocks are made rather than existing as free gas.
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