Gate 2011 1.3

1.3 The P-wave velocity of the earth’s mantle at the Mohorovicic discontinuity is

 (A) 5.5 km/s 

(B) 6.0 km/s 

(C) 7.0 km/s

(D) 8.0 km/s 

The Moho is the boundary between the crust and the mantle in the earth.

 The boundary is between 25 and 60 km deep beneath the continents and between 5 and 8 km deep beneath the ocean floor.

Typical values for P-wave velocity in earthquakes are in the range 5 to 8 km/s. The precise speed varies according to the region of the Earth's interior, from less than 6 km/s in the Earth's crust to 13.5 km/s in the lower mantle, and 11 km/s through the inner core.

2011 1.2

1.2 Which of the following rocks contributes to the highest amount of radioactive heat in the earth’s crust?

(A) basalt

(B) gabbro

(C) dunite

(D) Granite

GRANITE: It mainly consists of a larger part of earth crust and mostly contain alkali feldspar (K- felds part) & Quartz with small amount of other accessory minerals Since K (potassium) is a radioactive element because of its hight abundancy contributes to the highest amount of radioactive heat in the earth crust