Magnetic Field of Earth

The magnetic field of Earth is an invisible force that surrounds the planet. It acts like a giant bar magnet running through the middle of Earth, with one end near the North Pole and the other end near the South Pole. The field reaches out from the ground and stretches far into space. It protects life on Earth from dangerous particles coming from the Sun.

The field is made deep inside the planet. Earth's outer core is a thick layer of melted iron and nickel, about 1,800 miles below your feet. This metal moves and swirls as Earth spins. The motion of the hot liquid metal creates electric currents, and those currents create the magnetic field. Scientists call this process the geodynamo.

You can see the field at work with a compass. The needle inside a compass is a small magnet. It lines up with Earth's field and points toward the magnetic north pole. People have used compasses to find their way for almost a thousand years. Without Earth's magnetic field, a compass would just spin.

The field also shields the planet. The Sun sends out a stream of fast-moving particles called the solar wind. If those particles hit the surface, they would damage living things and strip away the air. Instead, Earth's magnetic field bends most of the solar wind around the planet, like a river flowing around a rock. Some particles get caught in the field near the poles. When they crash into gases high in the air, they make the glowing colors of the northern and southern lights.

Earth's magnetic field is not steady. The poles move a little every year, and the whole field can flip. When that happens, the magnetic north pole becomes the magnetic south pole, and the south pole becomes the north. Rocks that formed long ago hold a record of these flips, like a frozen compass reading. Scientists have counted hundreds of pole reversals over the last 80 million years. The last full flip happened about 780,000 years ago, long before modern humans built the first cities.

Why the field flips, and exactly when the next flip will come, is still an open question. Scientists do not think a flip would end life on Earth, but it could weaken the field for thousands of years and make some technology, like satellites and power grids, harder to protect. The Sun's particles never stop coming, and Earth's invisible shield never stops working.