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# Magnetic Evidence for Seafloor Spreading

## Magnetic polarity reversals in seafloor basalts are evidence for the creation of new seafloor at mid-ocean ridges.

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Flip-Flopping Field

### Flip-Flopping Field

Credit: Dr. Gary A. Glatzmaier - Los Alamos National Laboratory - U.S. Department of Energy
Source: http://en.wikipedia.org/wiki/File:Geodynamo_Between_Reversals.gif

The concept that the magnetic field reverses causes many people to ask the question, “But what are things like during a reversal?”

#### Why It Matters

Earth’s magnetic field is generated by currents in the planet’s molten iron outer core. The currents change over time and so the magnetic field does too. Sometimes the magnetic north pole becomes the magnetic south pole and vice versa. There is no set time between flips, but the average is about 450,000 years. The last one was 780,000 years ago. Uh oh! It appears that we are due for a magnetic field reversal! There are some signs that one is coming. Scientists are trying to learn what we should expect when one inevitably happens.

#### Explore More

1. To which magnetic pole does the N side of a compass point? Which geographic pole is nearest that magnetic pole? What name do we give to the magnetic pole the N side of the compass needle points to?
2. What are two reasons scientists have found that the magnetic field could be getting ready to flip? Based on the average for this time period, when should the pole flip?
3. What could happen to life on Earth during a magnetic field reversal?
4. What seems to happen to life on Earth during a magnetic field reversal? Where does this information come from?

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