In addition to paleomagnetism, what other evidence was needed to determine the rate of seafloor spreading?

A the strength of the magnetic field

B the age of each strip of rock

C minerals in the rocks

D the thickness of the rock layers

What causes the earth’s magnetic field?

A currents in the earth’s liquid-metal outer core

B magnetic particles located at the earth’s poles

C molten material in the mantle

D the mineral composition of the earth’s crust