In another EarthDate, we talked about Earth’s magnetic polarity reversing.

But sometimes the poles don’t flip, they just go on an excursion—with potentially drastic consequences.

A polar excursion happens when the pole moves more than 45 degrees from Earth’s rotational axis. This happened 12 times in the last million years.

Forty-two thousand years ago, there was a particularly wayward North Pole.

It wandered down to New York, then all the way to Antarctica, before rising back up to its original position.

The excursion took nearly a thousand years. While the pole traveled, Earth’s magnetic intensity fell, to as low as 6 percent—which is what caused the trouble.

You may remember from another EarthDate that Earth’s magnetic field protects us from cosmic rays. With it almost gone, much more radiation could reach Earth.

New data from this period suggests that increased cosmic radiation eroded the ozone layer and altered global wind patterns, causing dramatic climate change.

Ice sheets advanced in the higher latitudes. Drought swept across the middle latitudes. Megafauna went extinct in Australia. Neanderthals went extinct in Europe.

And cave art flourished, perhaps as humans took shelter from weather and harmful solar radiation.

It’s hard to say how much is correlation versus causation. But the poles are always wandering. If a pole goes on an excursion, we may find out for ourselves the effects of a reduced magnetic field.