Complete the following analogy.
asthenosphere is to mantle convection as is to earth's magnetic field.
a. outer core
b. lower mantle
c. radioactive material
d. asteroid bombardment

The earth has four layers; the crust, the mantle, the outer core and the inner core. The Earth’s magnetic field is the combination from the convection it receives from the outer core and the Coriolis Effect. The answer is letter A. The outer core is composed mostly of liquid nickel and iron. It is expected to have that state of metal because it has a higher temperature. The inner core cannot hold much of the magnetic field because of its high temperature and high pressure that exceeds the outer core. The temperature decreases however as the layer goes outwards.