This is

60 Second Science. I'm Annie Sneed.

Earth's magnetic field, which creates our planets north and south pole

is far from fixed.

In fact, the fuel is quite active, sometimes it

weakens and even reverses causing Earth's polarity to switch.

Reversals don't happen very often though, only about every 100,000 to million years.

That's part of why this phenomenon has largely remained a mystery for scientists.

However, a recent study may help researchers better understand how long and how complicated

Earth's magnetic field reversals really are.

The last polarity reversal took place some 770,000 years ago.

In a new study, researchers use lava flow records along with sedimentary and

Antarctic ice core data to examine that event.

They found that the reversal took about as long as many scientists previously believed it did,

just a few thousand years, But the researchers also examined the period prior

to that final reversal process and they discovered that a lot was happening with

Earth's magnetic field thousands of years beforehand.

There's clear evidence from the volcanic rocks

of a major excursion happening at about 795,000 years ago.

Brad Singer, a geoscientist at the University of Wisconsin-Madison, who led the study.

And that was followed by another excursion, which is the unexpected finding of this study at about 784,000. The two excursions that we've discovered in the

lava record and are seen in some of the sedimentary records are a sign that the dynamo

...