Earth's Magnetic Field Flips About Every 300,000 Years

North on a compass has not always pointed the same way. NASA explains that Earth’s magnetic field comes from the planet’s rapid rotation and its molten nickel-iron core, and that the magnetic polarity of Earth can change, flipping the direction of the field. The geologic record tells scientists that a magnetic reversal takes place about every 300,000 years on average. The average hides a lot of variation, and NASA stresses that the timing is very irregular. There is no reason for alarm. As far as we know, NASA says, such a reversal does not cause any harm to life on Earth, and one is very unlikely to happen for at least another thousand years. The magnetic field does useful work in the meantime. It traps charged particles from the Sun, which collide with the air over the poles and create the northern and southern lights.