A new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the Earth's magnetic field could change polarity in less than 100 years. The last magnetic reversal occurred some 786,000 years ago and was previously thought to have taken several thousand years but, if the researchers are right, the real time it may take for the flip to occur could actually be closer to the span of a human life.
At the heart of the Earth is a solid inner core of iron with a temperature of around 5,700° C (10,200° F), and about two thirds of the size of the Moon. It is solid at this temperature because of immense gravitational force, however, it also has an outer layer about 2,000 km (1,240 mi) thick composed mainly of iron and nickel that is fluid. It is the flow and movement of this liquid iron that generates electric currents which, in turn, create magnetic fields.
Changes in temperature, the flow up and down of various metals, and reactions to centuries-long changes in composition densities are all theorized to be in some way responsible for the shift in the direction and intensity of this magnetic field.
The new research into this phenomenon is based on measurements taken of the magnetic field alignment of sedimentary layers in a prehistoric lake site in the Sulmona basin of the Apennine Mountains east of Rome, Italy, which show the change in magnetic alignment of material captured as sediment and frozen in time.
An Italian research team led by Leonardo Sagnotti of the National Institute of Geophysics and Volcanology measured the magnetic orientations contained in the sediments that amassed on the ancient lake bed and, because the lake sediments were laid down at a large and consistent rate over a 10,000-year period, the team was able to interpret the date of the layer containing the reversal of the magnetic field. Known as the Matuyama-Brunhes transition, this period occurred – according to the researcher’s dating tests – fairly close to 786,000 years ago.
When the ancient body of water existed, it was upwind from a province of high volcanic activity that included periodically erupting volcanoes near Sabatini, Vesuvius, and the Alban Hills. With ash layers distributed and interspersed on this former lake, the researchers were able to use argon-argon dating to determine the age of the ash layers situated above and below the layer of sediment that chronicled the last reversal. As a result, the date determined is far more precise than that of earlier studies, which had previously placed the reversal somewhere between 770,000 and 795,000 years ago.
According to the research, about 789,000 years ago the north magnetic pole started wandering around Antarctica. This lasted for several thousand years before suddenly reversing 786,000 years ago to roughly the point we know it in today in the Arctic.
"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."
This new research comes at a time when fresh evidence points to the fact that the intensity of Earth's magnetic field is decreasing at a rate 10 times faster than expected, which has led some geophysicists to predict a reversal sometime within the next few thousand years. Though such a magnetic reversal would be a significant global event, there is no major evidence from geological and biological records that this was in any way catastrophic for life with past reversals.
Today, however, a reversal could theoretically wreak havoc with electrical grids from the collapse or change of electrical fields or – worse still – a period of indeterminate magnetic fields on the way to a full reversal may see cancer rates rise as radiation previously deflected by the Earth’s magnetic field may be allowed to bombard the planet.
"We should be thinking more about what the biologic effects would be," said Professor Paul Renne, director of the Berkeley Geochronology Center.
This is the most worrying aspect of the findings of this research, as the sudden 180-degree reversal of the magnetic field had a period of severe instability before it that lasted over 6,000 years with two intervals of about 2,000 years each that showed exceptionally low magnetic field strength. The complete magnetic polarity flip occurred somewhere near the end of the last of these low field strength intervals.
"What’s incredible is that you go from reverse polarity to a field that is normal with essentially nothing in between, which means it had to have happened very quickly, probably in less than 100 years," said Professor Renne. "We don’t know whether the next reversal will occur as suddenly as this one did, but we also don’t know that it won’t."
The results of the research will be published in the Geophysical Journal