At the present rate, Earth’s magnetic field could be gone within a few centuries, exposing the planet to the relentless blast of charged particles from space with unpredictable consequences for the atmosphere and life. Other possibilities: the field could stop weakening and begin to strengthen, or it could weaken to the point that it suddenly flips polarity — that is, compasses begin to point to the South Magnetic Pole.
An even older record of Earth’s fluctuating field than Shaw refers to shows a more complicated picture. Ancient lava flows from the Hawaiian Islands reveal both the strength of the field when the lava cooled and its orientation — the direction of magnetic north and south. “When we go back about 700,000 years,” says geologist Mike Fuller of the University of Hawaii, “we find an incredible phenomenon. Suddenly the rocks are magnetized backwards. Instead of them being magnetized to the north like today’s field, they are magnetized to the south.”
Such a reversal of polarity seems to happen every 250,000 years on average, making us long overdue for another swap between the north and south magnetic poles. Scientist Gary Glatzmaier of the University of California at Santa Cruz has actually observed such reversals, as they occur in computer simulations (view one in See a Reversal). These virtual events show striking similarities to the current behavior of Earth’s magnetic field and suggest we are about to experience another reversal, though it will take centuries to unfold.
Some researchers believe we are already in the transition phase, with growing areas of magnetic anomaly — where field lines are moving the wrong way — signaling an ever weaker and chaotic state for our protective shield.