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