UNIVERSE
PLANETARY INTERIORS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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The crust is denser than the mantle is
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The crust is liquid and the mantle is solid
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The crust is solid and the mantle is liquid
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The crust is less dense than the mantle
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Detailed explanation-1: -What is Moho Discontinuity? The ‘Moho Discontinuity’ is the boundary between the crust and mantle. It has been named so as it was discovered by Croatian Seismologist Andrija Mohorovicic. This boundary marks a change in the seismic waves velocity from the crust to the uppermost mantle within the lithospheric plate.
Detailed explanation-2: -This sudden velocity change shows us that at the Moho, there is a significant change in the density of the material. The layer beneath the crust (the mantle) is more dense than the crust, and so the P-waves speed up when they enter it. Moho: What is It?
Detailed explanation-3: -Seismic waves tell us that the Earth’s interior consists of a series of concentric shells, with a thin outer crust, a mantle, a liquid outer core, and a solid inner core. P waves, meaning primary waves, travel fastest and thus arrive first at seismic stations. The S, or secondary, waves arrive after the P waves.
Detailed explanation-4: -P waves would decrease in speed and S waves would disappear.
Detailed explanation-5: -Seismic velocities tend to gradually increase with depth in the mantle due to the increasing pressure, and therefore density, with depth. However, seismic waves recorded at distances corresponding to depths of around 100 km to 250 km arrive later than expected indicating a zone of low seismic wave velocity.