Equatorial Alaska

It has now been well established that the continents do not remain fixed on the earth's surface, but wander around willy-nilly, sometimes bumping into one another and sometimes splitting apart. Of course, at the rate they move, it takes quite a bit of time for them to get from one place to another.

Professor David Stone and his co-workers at the Geophysical Institute have been working for a number of years trying to reconstruct Alaska from its original pieces, and to determine where the pieces came from.

Stone uses the principles of paleomagnetism. This science relates to the fact that most rocks contain grains with magnetic properties. When the rocks solidify, either from a molten state or by the slow compaction of sediments, the magnetic minerals which they contain assume a orientation parallel to the lines of the earth's magnetic field at that place and time.

It is reasonably certain that the magnetic poles of the earth have always been in fairly close proximity to the geographic poles. The magnetic field lines point nearly vertically at the poles (this is the reason compasses do not work well at high latitudes) and nearly horizontally at the equator.

Rocks formed at either of these locations would therefore be permanently magnetized in those directions at the time of solidification, while rocks formed at intermediate latitudes would exhibit a "dip" in their magnetic fields representative of the latitude.

If the rocks can be dated and the dip of the ancient magnetic field measured, it is therefore possible to determine how far from the poles they were at the time they solidified.

Sampling rocks from around Alaska, Stone and his group find evidence that Alaska has always been a wanderer. In fact, back in the Permian Period, 250 million years ago when the first dinosaurs were about, it was even tropical.

Not only that, it wasn't even in one piece! The picture emerging is that Alaska was fragmented during the Permian, meandering across the equator from north to south, and then finally got its act together about 160 million years ago and moved back north as a unit.

If all this sounds a bit improbable, consider that at rates that can be observed and measured today, part of California west of the San Andreas fault will arrive in Alaska sometime during the next 60 million years.