In the d" layer, the portion of the mantle closest to the core-mantle boundary is hypothesized to be partially melted because the s-wave velocities decrease by 30% when passing through it.
a) true
b) false

True

Explanation:

The D layer is a transition zone between the solid portion of the lower mantle and the liquid outer core. Because S-waves only travel through solids, it has been hypothesized that a partially molten transition zone would affect the velocity of these S-waves by slowing them down considerably as the rock layer becomes less solid. The waves that are able to travel through a non-solid medium are the P-waves, which are more energetic than S-waves.

the answer is crop rotation

c. seafloor spreading occurs.

d. crust becomes molten rock.

e. denser plates slide under lighter plates.