#laschamp

Earth’s magnetic field is generated by convection in the outer core, a molten layer of iron-nickel metal that is capable of carrying and moving electrical charges. This is an extremely complicated process which humans currently don’t have the full capability to simulate. Imagine a river flowing – every little rock, every little difference in the flow path of the water, can cause turbulent flow in the river. Although there are dominant features to the convection in the outer core, complexity in the flow will show up as complexity at the surface. Earth’s magnetic field is dominantly a dipole field, meaning that it has north and south pole components closely aligned with the north and south poles around which the planet rotates. However, some portion of the magnetic field is always taken up by the more complicated components generated by the complex circulation in the core; this will cause some areas to be stronger and other areas to be weaker than the average magnetic field at any given time. Sometimes, the Earth’s dipole, north-south magnetic field appears to decrease in strength to zero, and then suddenly flip – with the south pole and north pole changing places. Because there are minerals on earth that record the magnetic field direction and intensity when they form, these magnetic reversals can be quite precisely recognized and studied. The last time the magnetic field fully flipped was about 781,000 years ago. Since then, the magnetic pole has mostly remained aligned with the north rotation pole, but the magnetic field is constantly in a state of change. The graph with this post shows the strength of the magnetic field over the past 100,000 years in the red curve, with today at 0 on the x axis. As you can see, the magnetic field has slightly weakened over the past 2000 years, but that was after a long period of strengthening of the field. Thus, weakening of the field right now is totally normal and not a sign of any pending 2020 apocalypse. At present, the South Atlantic Magnetic Anomaly has a strength that is about ½ that of the strongest magnetic field zone on Earth, and maybe about 3/4 that of the average, overall magnetic field. While this is the largest weak area on earth, you can also see from this graph that a weaker magnetic field than the one observed today is a common feature in recent geologic history, and does not portend an upcoming reversal. The blue line on that plot shows one other thing – how far away from the rotational pole is the current magnetic field. For most of the last 100,000 years the field has remained nearly north-south, but of course you can see one anomaly – 41,000 years ago, during an event called the Laschamp excursion, the north-south magnetic field weakened to nearly zero, and a weak east-west magnetic field seemed to dominate. Even though this event occurred and the total magnetic field shifted substantially, within a few centuries it snapped back to the previous orientation without reversing. If the magnetic field were to decay away, anything on the surface would be exposed to additional radiation and magnetic currents associated with the sun. This would generally be bad for humans, and in particular for electronic equipment, much of which would need additional shielding. In fact, satellites heading over the South Atlantic Magnetic Anomaly do need to prepare for these effects right now. But, if it helps to put your mind at ease – geologic history tells us that small changes in the magnetic field are normal and have happened constantly over the past 100,000 years. Not only do they not necessarily mean anything big is about to happen, we also see that it requires centuries of weakening before we would be concerned about the magnetic field truly dropping to zero, and that should be time for the next generations of electronics to receive extra shielding. If you’re wondering what the next hazard of 2020 will be, weakening of the magnetic field doesn’t have to be on your list, unless you’re designing a satellite. -JBB Image credit and references: https://eos.org/editors-vox/the-global-geomagnetic-field-of-the-past-hundred-thousand-years https://www.livescience.com/nasa-monitoring-dent-earth-magnetic-field.html https://www.nbcnews.com/science/science-news/dent-earth-s-magnetic-field-puzzles-scientists-n1237328