Multiple choice

Consider the following statements regarding Earth's topmost layer:

  1. Transverse earthquake waves move at a speed of 3.5 km/second in that layer.
  2. The specific gravity is 2.7.
  3. It is shallowest under the continents and deepest under the oceans.
  4. Magnesium is present in abundance.

Which of the above statements are correct?

  1. 2 and 3

  2. 1 and 2

  3. 1, 2 and 4

  4. 3 and 4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The Earth's topmost layer (the continental crust) has a specific gravity of about 2.7 and seismic waves (P-waves) travel through it at roughly 6-7 km/s, though S-waves are slower. Statement 3 is incorrect because the crust is thickest under continents and thinnest under oceans. Statement 4 is incorrect because the continental crust is primarily granitic (rich in silica and aluminum), not magnesium-rich (which is characteristic of the oceanic crust).

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