Earth’s geomagnetic field helps many living things orientate themselves, which includes humans who use a compass. But the field also plays a more crucial role: it projects out into space and protects everything on the planet’s surface from particles streaming from our Sun. This dangerous, high-energy radiation can tear apart fragile DNA, kill cells and cause cancers.
Our planet’s magnetic field is often represented as a giant bar magnet inside the Earth, with the North and South poles corresponding roughly with their geographical positions. In reality though, the magnetic field is far more complex, with different intensities at different points on the Earth’s surface, changing direction over time.
And every 250,000 years or so, the field flips around completely. These geomagnetic reversals – slow events taking 5,000-10,000 years to complete – cause the overall strength of the field to decrease and the main poles to fade, temporarily replacing them with multiple, small and local magnetic north and south poles. The Earth has experienced hundreds of reversals in its history: the last one happened 780,000 years ago, which means we’re due another.
When the last reversal occurred, life survived. “All of the plants and animals that we have today were around at that time too,” says geophysicist Dr Ciaran Beggan of the British Geological Survey. “Therefore there cannot be any particularly harmful effects on the flora and fauna of the planet as a whole, considering reversals are frequent relative to the lifetime of a species.”
But while humans might survive, a magnetic reversal could cause the end of civilisation as we know it – by damaging modern technology. To deal with the extra radiation, we would have to redesign low-orbit satellites and the surface infrastructure. “Large power grids, pipelines and railways would have to include protection against geomagnetically induced currents during solar storms,” explains Beggan, adding that because the reversals last thousands of years, mankind might have enough time to adapt its technology.
Odds of human extinction: 10,000-1