The shield of our planet is weakening, some researchers see it as signs of the next pole shift. A new study gives the all-clear.
Unlike bees, sharks or migratory birds, we , humans, do not orient ourselves using the Earth’s magnetic field. But we nonetheless owe it our survival: It shields us from deadly radiation from outer space, especially from the stream of charged particles of the solar wind. But this shield of our planet is not really stable: the global strength of the Earth’s magnetic field has been decreasing by about five percent per century since record keeping began in 1840.
Since then, a weak zone has formed over the southern Atlantic where increased radiation activity can be detected. Researchers call this phenomenon the “South Atlantic Anomaly” and are at odds whether it is a sign of a magnetic pole reversal.
The results of a study conducted by a team led by Maxwell Brown and Monika Korte of the German Geo Research Center in Potsdam go against the assumption of an upcoming pole switch. According to this, in the past 50,000 years at least twice comparable anomalies over the South Atlantic had emerged, but the geomagnetic field recovered again, a pole shift did not occur. Phases of a short-term actual pole reversal followed a distinctly different pattern.
From a geological perspective, pole shifts are not a rare phenomenon; on average, the Earth’s magnetic field reverses every 250,000 years. The last lasting reversal took place about 780,000 years ago and was rapid – within a century at the most. Against this background and in view of the increasing South Atlantic anomaly, researchers have repeatedly warned in recent years that a renewed pole shift could be imminent in the coming decades.
Although such an event is always followed by periods of long stability, the process is initially associated with very low field strengths, so the Earth is exposed to significantly higher levels of cosmic and solar radiation. Not only do scientists expect disruptions in communication technology, but also a massive increase in cancer. Some paleontologists even speculate that several successive polarity reversals of the Earth’s magnetic field triggered a massive extinction and the subsequent Cambrian explosion about 550 million years ago.
For their study, Korte and colleagues now reconstructed changes in the Earth’s magnetic field in the period 50,000 to 30,000 years ago. They used data from sediment cores and volcanic rocks, which contain magnetic minerals, which in turn provide information about the orientation and strength of the Earth’s magnetic field at the time of their formation.
The result: About 46,000 and 49,000 years ago, the geomagnetic field over the South Atlantic formed similar weak zones as today. But in both cases, the anomaly disappeared again after some time. 41,000 years ago, however, there was a short-term reversal of polarity, which lasted only a few centuries and is therefore not considered a pole shift, but as a magnetic excursion.
This event was preceded by a distinctly different pattern of development than the one observable today, says Korte: “From our consideration of the past 50,000 years, we conclude that today’s South Atlantic anomaly can not be interpreted as the beginning of a field reversal.”