We have completed maintenance on DiscoverMagazine.com and action may be required on your account. Learn More

Why Does the Earth's Magnetic Field Flip?

And how does that affect the planet's creatures?

Oct 1, 2004 5:00 AMNov 12, 2019 5:50 AM


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.

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.