April Flowers for redOrbit.com – Your Universe Online
Imagine waking up after a night of camping to find that your compass is pointing south rather than north. It can happen. The magnetic field around Earth has flipped before — though not overnight. In fact, it has happened many times throughout the planet’s history.
The magnetic field, which is dipolar like a magnet, remains at a steady intensity for thousands to millions of years, then, for some unknown reason, it weakens and reverses direction over a few thousand years.
A new study, published in an upcoming issue of Geophysical Journal International, demonstrates that the last magnetic reversal happened around 786,000 years ago. The reversal happened very quickly. According to the research team from Italy, France, Columbia University and the University of California, Berkeley, that reversal happened in less than 100 years, which is roughly a human lifetime.
“It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”
The findings have serious implications as recent evidence has demonstrated that the Earth’s magnetic field is weakening 10 times faster than normal, which has some geophysicists suggesting that a reversal will happen within a few thousand years.
Image Above: The ‘north pole’ — that is, the direction of magnetic north — was reversed a million years ago. This map shows how, starting about 789,000 years ago, the north pole wandered around Antarctica for several thousand years before flipping 786,000 years ago to the orientation we know today, with the pole somewhere in the Arctic. Credit: UC Berkeley
Such a reversal would represent a planet-wide event driven by convection in the Earth’s iron core. Despite this, the geologic and biologic records do not show any documented catastrophes associated with reversals in the planet’s past. With our current electric grid, however, a reversal of the field could be hazardous.
Earth is protected from energetic particles released from the sun and cosmic rays — both of which cause genetic mutations — by the magnetic field. The weakening of the field which occurs before a reversal could increase cancer rates, and long periods of unstable magnetic behavior could cause even more havoc.
“We should be thinking more about what the biologic effects would be,” said Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in-residence of earth and planetary science.
IBT reports that the team used argon-argon dating to measure magnetic field alignment in layers of ancient lake sediments exposed in the Sulmona basin of the Apennine Mountains east of Rome, Italy.
They found that the Mauyama-Brunhes transition layer shows the last reversal at around 786,000 years ago. The speed of the reversal is indicated by the normal field in the adjacent layer with nothing in between. Before the flip, a period of nearly 6,000 years of instability existed, including two intervals of low magnetic field strength that lasted about 2,000 years each.
Recently, scientists using a satellite array called Swarm have detected a weakening in the magnetic field — and that magnetic north is moving towards Siberia.
Previous studies estimated the weakening at about 5 percent per century, but the new Swarm data has revised that estimate to 5 percent per decade.