Speaker: Dr Jon Mound, University of Leeds
Sunday 9 November 2014
This week we were joined by Dr Jon Mound from the University of Leeds, who gave a fascinating talk about the physics of the Earth’s magnetic field. As Jon explained, the magnetic field around the Earth is produced by the spinning currents in the molten iron outer core of the Earth and protects us by deflecting harmful radiation from the Sun. The magnetic field has a north pole (as pointed to by compasses) and a south pole, which reverse positions roughly four times every million years. We can see this in the arrangment of magnetic particles embedded in rocks formed at different times in the Earth’s history.
Ever since we have started to measure the strength of the magnetic field, it has been weakening. This, coupled with the fact that it is way ‘overdue’, could indicate that a flip is about to occur. However it can be very difficult to predict as the time between reversals is very irregular. The weakening of the field would result in more radiation reaching us from the Sun, which could cause major damage to satellites and infrastructure such as the National Grid, which are susceptible to hits from charged particles. It could also have an effect on the climate as the particles interact with weather systems. The magnetic field is still used for navigation by humans, and also many animals, such as homing pigeons, many small mammals and even spiny lobsters are sensitive to the magnetic field (known as magnetoception). A flip in the polarity could cause confusion for these animals. That said, they’ve survived many magnetic flips in the past!
As Jon summarised, we may be a long, long way off from another magnetic field flip. If it does come soon, it could cause some damage to our communication systems, but it is something we could easily prepare for by building some extra shielding, and certainly nothing to panic about!