Course: Science Subtest I
Lesson: Dynamic Processes of the Earth (Geodynamics)
Topic: Tectonic Processes I: Continental Drift      Page 12 of 15  

Paleomagnetic evidence for continental drift. This evidence came long after Wegener, but it is strong evidence that continents move on the surface of the Earth.

Some lava flows, mostly basalt, contain magnetic minerals, called magnetite, that line up with the Earth's magnetic field. These tiny magnets are frozen in place as the lava flow cools, recording the location of the planet's magnetic north pole at the time the basalts formed. This ancient magnetism is known as paleomagnetism.

Scientists in the 1950s used magnetite to locate the magnetic north pole over geologic time. They found that rocks that formed at the same time on the same continent pointed to the same north magnetic pole. But the magnetic north pole recorded by older rocks was not in the same location as the current magnetic north pole. Scientists also noticed that rocks that formed at different times on the same continent pointed to different north magnetic poles. That is, the north magnetic pole of a continent appeared to wander over time.

There are three possible explanations for this: (1) The continents were stationary but the north magnetic pole moved over time. (2) The north magnetic pole was stationary but the continents moved over time. (3) Both the pole and the continents moved over time.