Geology Reference
In-Depth Information
magnetic currents emitted by other animals. For example, the great white shark can orient itself toward
mammalian prey several feet away by detecting the electromagnetic pulses of its heartbeat traveling
through the water.
Figure 8-7:
The rel-
ative age of
oceanic crust
along the seafloor
of the Atlantic
Ocean.
The sequence of magnetic reversals and patterns of older rocks situated farther from
the rift indicate that the oceanic plates are spreading out from the Mid-Atlantic Ridge as
new rock is formed. This evidence leads to the conclusion that new ocean crust is being
created along the ridge as the oceanic plates move apart from one another. (I further ex-
plain the creation of rocks along the Mid-Atlantic Ridge and in other similar areas of the
earth in Chapter 10.)
Measuring plate movements
After scientists recorded that crustal plates had indeed moved, they sought a way to de-
termine the rate, or
velocity,
of plate movement.
