Consider the following statements regarding the Earth’s crust:

I. The continental crust is thinner under fold mountains.

II. The mean thickness of ocean crust is 30 km.

III. The Earth’s crust is brittle in nature.A.I onlyB.I and IIC.III onlyD.I and III

Question

Consider the following statements regarding the Earth's crust: I. The continental crust is thinner under fold mountains. II. The mean thickness of ocean crust is 30 km. III. The Earth's crust is brittle in nature.

Accepted Answer

III only. Statement I is wrong. Continental crust is actually thicker, not thinner, under fold mountains. Fold mountains form when plates push together and compress the crust, forcing rock upward into peaks. The same compression also pushes rock downward, creating a deep crustal root beneath the range. Because of this, crust under the Himalayas can reach nearly 90 kilometres thick, far more than average. Statement II is wrong. Ocean crust averages only around 6 to 10 kilometres, not 30 kilometres. A thickness of about 30 to 40 kilometres actually describes average continental crust, not oceanic crust. Statement III is correct. The crust is solid, rigid rock, and it genuinely behaves as brittle material. This is unlike the hot, semi-solid mantle below it, which can slowly flow instead of cracking. So only statement III holds true, making option (c) the answer.

Consider the following statements regarding the Earth’s crust: I. The continental crust is thinner under fold mountains. II. The mean thickness of ocean crust is 30 km. III. The Earth’s crust is brittle in nature.

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