about 22,000 years

During an excursion or a reversal, the magnetic field is considerably weakened and allows many more cosmic rays to reach the surface of the planet. These energetic particles from space can be damaging to life on Earth if too many reach the surface.

200,000 to 300,000 years

The cause is likely accelerations in the flow of liquid iron near Earth’s core. Earth’s magnetic field protects our planet from unhealthy solar radiation. Earth’s continuously changing magnetic field is thought to be largely generated by superheated, swirling liquid iron in Earth’s outer core.

We know that the Earth’s poles have reversed hundreds of times. It’s a dynamic system inside the outer core and it has to reverse at times because that’s just part of the way it works. We know it’s done this most recently 780,000 years ago, so there are people who say it’s overdue.

What would happen if Earth suddenly lost its magnetic field? The most obvious effect is that we would get lost, since our compasses wouldn’t work. Less obvious is that without the magnetic field the solar wind would strip away ozone from Earth’s atmosphere and leave us exposed to ultraviolet radiation.

Extending from Earth like invisible spaghetti is the planet’s magnetic field. Created by the churn of Earth’s core, this field is important for everyday life: It shields the planet from solar particles, it provides a basis for navigation and it might have played an important role in the evolution of life on Earth.

The source of the magnetic field is the iron-rich liquid outer core of the Earth. This liquid moves in complex ways as a result of the convection of the heat deep within the core and of the rotation of the planet. The motion of the core fluid is continuous and never stops, even during a reversal.

There’s the geographic North Pole, which never changes. And there’s the magnetic North Pole, which is always on the move. And right now it’s moving faster than usual. Over the past 150 years, the magnetic North Pole has casually wandered 685 miles across northern Canada.

There are three main sources of heat in the deep earth: (1) heat from when the planet formed and accreted, which has not yet been lost; (2) frictional heating, caused by denser core material sinking to the center of the planet; and (3) heat from the decay of radioactive elements.