year old lava flows in North America indicated that the north magnetic pole was located in
the western Pacific Ocean, but 250 million year old lava flows indicated a pole in Asia, and
100 million year old lava flows had a pole in northern Asia. Scientists were amazed to find
that the north magnetic pole changed location through time (Figure6.9)!
Figure 6.9: The magnetic north pole appears to move around with time. This diagram shows
where the pole was 80 million years before present (mybp), then 60, 40, 20 and now. Since
we know that the pole does not move, this path is called apparent polar wander. ( 11 )
There were three possible explanations for this puzzling phenomenon: (1) the continent
remained fixed and the north magnetic pole moved (2) the north magnetic pole stood still
and the continent moved (3) both the continent and the north pole moved.
The situation got stranger when scientists looked at where magnetite crystals pointed for
rocks of the same age but on different continents. They found these rocks pointed to different
magnetic north poles! For example, 400 million years ago the European north pole was
different from the North American north pole at that same time. At 250 million years, the
north poles were also different for the two continents. The scientists again looked at the three
possible explanations. If the correct explanation was that the continents had remained fixed
while the north magnetic pole moved, then there had to be two separate north poles. Since
there is only one north pole today, they decided that the best explanation had to involve
only one north magnetic pole. This meant that the second explanation must be correct, that
the north magnetic pole had remained fixed but that the continents had moved.
To test this, geologists fitted the continents together as Wegener had done. They discovered
that there had indeed been only one magnetic north pole but that the continents had drifted.
They renamed the phenomenon of the magnetic pole that seemed to move but actually did
notapparent polar wander. This evidence for continental drift gave geologists renewed
interest in understanding how continents could move about on the planet’s surface. And
we know that the magnetic pole wanders, too, so the correct explanation was that both the