The discontinuity that separates the outer core from the inner core is called the
- A.Repetti discontinuity
- B.Lehmann discontinuity
- C.Moho discontinuity
- D.Conrad discontinuity
Correct answer
Explanation
The correct answer is B, the Lehmann discontinuity. It marks the change from the molten outer core to the solid inner core, and is named after Inge Lehmann, who deduced from the behaviour of earthquake waves that the innermost part of the planet is solid.
Option A, the Repetti discontinuity, lies far above it, between the upper and the lower mantle. Option C, the Moho or Mohorovicic discontinuity, is the crust and mantle boundary and is the shallowest of the named surfaces after the Conrad. Option D, the Conrad discontinuity, lies within the crust itself, dividing its upper and lower parts. Candidates lose this mark by learning only two names, so list all five from the surface downward: Conrad, Moho, Repetti, Gutenberg and Lehmann, and attach one depth to the list, the 2,900 kilometres of the Gutenberg surface, since that figure anchors every other layer in the diagram.
Read the full article: Structure of the Earth and Rocks: Layers, Waves and Types
Practice Questions
View allThe boundary that separates the crust from the mantle is known as the
- A.Conrad discontinuity
- B.Mohorovicic discontinuity
- C.Gutenberg discontinuity
- D.Lehmann discontinuity
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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.
Read the full explanation →Which 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.
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