Dr. Chang is studying seismic waves. He notices that seismic waves (a type known as P-waves) travel faster through the mantle than through the outer core. What can he conclude from this observation?
A.
The mantle is wider than the inner core.
B.
The mantle is not as dense as the outer core.
C.
The inner core is wider than the mantle.
D.
The outer core is not as dense as the mantle.