Earthquakes, explosions and observations of Earth’s ever-changing magnetic field are helping scientists open up a new window on the heart of our planet. The magnetic field also acts as a protective barrier between us and some of the dangers of space, shielding us from radiation in the solar wind. The Earth’s magnetic field has been steadily weakening over the past 180 years. And there is one patch that is weakening faster than any other. It is an area scientists have dubbed the “South Atlantic Anomaly“, which sits over the South Atlantic and the centre of South America. It is a known hazard for spacecraft because it creates a dip in the field, allowing charged particles into the orbit of satellites and upsetting their electronics and instrumentation. But what some scientists suspect is that it could be much more than an inconvenience to satellite operators – it could be the first indication of a profound change in Earth’s magnetic field. When scientists mapped the Earth’s magnetic field down to the level of the outer-core, they discovered that under the South Atlantic Anomaly the simple north-south divide we know at the surface had broken down. There are patches where the field has actually flipped and points north instead of south. Using his weather analogy, Lathrop believes “a particularly violent or unusual patch of weather” in the molten metal of the outer-core is responsible for reversing the field. If these patches continue to deepen and spread, the entire Earth’s magnetic field could reach a tipping point and flip, he believes. It is not something that would happen overnight – it could take thousands of years, during which period the field would be pretty confused. The magnetic poles could wander to the equator for example, and take with them the spectacular Northern Lights. It would not be out of character – the shifting flows of the core have reversed Earth’s field hundreds of times before. “It’s not a question of if the Earth is going to reverse the magnetic field, but when,” says Lathrop. Exactly when this might be remains one of the core’s many mysteries. But after centuries of speculation, scientists are finally beginning to understand this great wonder lying 6,000km beneath our feet. -BBC