Register for an account


Enter your name and email address below.

Your email address is used to log in and will not be shared or sold. Read our privacy policy.


Website access code

Enter your access code into the form field below.

If you are a Zinio, Nook, Kindle, Apple, or Google Play subscriber, you can enter your website access code to gain subscriber access. Your website access code is located in the upper right corner of the Table of Contents page of your digital edition.


Why Does the Earth's Magnetic Field Flip?

And how does that affect the planet's creatures?


Sign up for our email newsletter for the latest science news

Why does Earth’s magnetic field sometimes flip over? Does such a reversal affect living things?

Joe Kirschvink, paleomagnetist and professor of geobiology at Caltech, answers:

Earth’s magnetic field is produced by electrical currents flowing within the hot liquid metal of the outer part of the planet’s core. Like gases in the atmosphere and water in the oceans, this fluid metal undergoes random fluctuations in temperature and motion, analogous to the weather patterns we experience up top. Occasional “storms” in the core are strong enough to flip the polarity of the magnetic field, although the process of reversal is usually quite slow, taking 3,000 to 10,000 years. Reversals are also rather rare events: On average, only three or four of them happen every million years.

Many animals—including bees, fish, pigeons, and whales—possess a specialized set of neurological receptors containing tiny magnets, which allow them to sense and navigate by the geomagnetic field. During reversals, Earth’s field weakens (although it does not disappear entirely), and the direction of magnetic north may vary wildly. During a single animal’s lifetime, however, most of these changes are probably too small to be noticed. There have been several thousand magnetic reversals since the evolution of animal phyla about 600 million years ago, so any creatures that experience seriously detrimental effects when a flip occurs have probably been removed by natural selection.

    3 Free Articles Left

    Want it all? Get unlimited access when you subscribe.


    Already a subscriber? Register or Log In

    Want unlimited access?

    Subscribe today and save 50%


    Already a subscriber? Register or Log In