evidence: Historically, the North Pole has moved at about 15 kilometres per year. But since the 1990s it has sped up, and now is moving at about 55 kilometres per year towards Siberia. It is speculation, but this might foreshadow a ‘magnetic reversal’ in which the magnetic north and south poles change locations. This has happened 171 times in the past 71 million years – and we are overdue a flip. [...] Scientists discovered magnetic reversals by measuring the magnetic field on either side of mid-Atlantic ridges from which molten rock is extruded like toothpaste from a tube. As it solidifies, its crystals align along the direction of the Earth’s magnetic field at the time, leaving a ‘tape recording’ of reversals. Reversals are believed to take place over 1,000 to 10,000 years, during which time the field shrinks to zero before growing again with the opposite polarity. There were therefore times – maybe even centuries – when the Earth had essentially no magnetic field.