Living Life on a Magnet
Thanks to a spinning globule of trillions of tons of partially molten iron beneath our feet, living things in most areas of the Earth’s surface are bathed in a geographically asymmetric field of magnetism. We humans appear to be insensitive to magnetic fields, and it took the invention of the magnetic compass to allow us to use the Earth’s magnetic field to help us navigate our way across the planet’s surface. However many other animals have highly developed magnetosensory skills that can enable them to orient themselves in the environment and to migrate over long distances with astonishing accuracy. Bacteria are more interested in the third dimension, and their usual use of magnetotaxis is to help them swim downwards, parallel to the magnetic field lines. Accordingly, bacteria from the Northern and Southern Hemispheres tend to have opposite magnetotactic swimming polarities to cater for the opposing inclination of the magnetic field.