YOU might be surprised to learn that you’re probably carrying a compass in your pocket right now. Although compasses seem old-fashioned, they’re so useful and reliable that smartphones use them to tell you which direction you’re facing.

Compasses use a tiny magnet to demonstrate the orientation of the Earth’s magnetic field. The magnetic field itself is generated from currents in the molten interior of our planet. Currents in such a vast volume of molten iron within the Earth which produce a magnetic field stretching out through the solid outer layers and into space.
 
And we are lucky that they do. By acting like a big bar magnet, the Earth’s core envelops us in a protective magnetic blanket, which shields the surface from high energy particles from the sun and outer space.

These high energy particles are deflected by the magnetic field and travel along the field lines to the magnetic poles where the field gets stronger and points down into the Earth. As the particles are brought closer to the surface they hit the upper atmosphere and burn up, emitting the beautiful colours of the Northern and Southern lights.
 
Without Earth’s magnetic field, we’d be exposed to a lot more carcinogenic high-energy radiation, and our power and communications systems would also be in trouble. The main source of danger is the Sun. Like the Earth, it also has magnetic fields. However, unlike the Earth’s, the fields are messy and break out randomly across the sun’s surface.

In particularly intense periods of violent magnetic rearrangement, sunspots appear — these are where concentrated magnetic fields prevent the normal emission of light.

During these periods, the sun also occasionally undergoes a “solar storm,” where magnetic field lines snap out, spewing high energy particles and radiation out into space. In particularly bad storms our magnetic shield is overwhelmed and we get a small taste of what it would be like to go without it.

As well as beautiful aurorae much closer to the equator, electromagnetic chaos charges up our power lines, preventing normal electricity transmission and causing huge blackouts.
 
The earliest evidence of the Earth’s magnetic field, in the form of ancient magnetised rocks, is from 3,450 million years ago. However, just like the Sun, the Earth’s magnetic shielding is constantly changing due to instabilities in its internal currents. The magnetic poles have randomly flipped back and forth over 150 times in the last 83 million years.
 
We are currently in a period of magnetic field decrease, alongside an acceleration in the movement of the magnetic North Pole, which is moving from Canada towards Siberia at a speed of around 40 km/year.

During a flip the Earth is left more exposed, but fortunately the process takes thousands of years and, unlike the rest of the imminent environmental collapse we observe around us, does not appear to be influenced by human activity.  
 
Evidence of just how stable the magnetic field really is comes from the wide range of animals that have evolved to detect its strength and direction.

Birds, insects, and even cows appear to be able to sense the Earth’s magnetic field and use this information for migration routes, or in the case of cows, simply choosing a direction to lie down. However, the sensing mechanism is only understood in a few species. For example, in chickens, iron mineral deposits in their beaks are believed to be crucial.
 
Whether humans are also capable of sensing magnetic fields has been highly disputed, with much research attempting to prove that such a sense exists. As many previous results have been found to be unreproducible (and therefore not credible), new reports are treated with strong scepticism. Nevertheless, such reports are frequent, although the quality is highly variable even in those that make it to print.

In February, for example, a tiny study was published claiming to show that exposure to blue light helped starving people sometimes to align themselves with the compass. Unfortunately, the study was tiny, and the effect even tinier, so that the statistics look highly questionable. A replication trial is unlikely to be attempted because the trial results were so poor.  
 
In contrast, in March this year a separate group of researchers hit the headlines when they showed that they could reliably produce a significant alteration in electrical activity in the brains of 34 volunteers when they reoriented an Earth-like magnetic field while the participant sat motionless in the dark.

The magnetic modulation dampened alpha-waves in the brain, signals famous for their occurrence in REM sleep and which also occur in wakeful relaxation (sitting still with your eyes shut). Intriguingly, the response only happened when the original field matched a realistic orientation for the Northern hemisphere (where the study took place) and when the change was equivalent to the north pole moving suddenly 90° anti-clockwise from North East to North West. The very specific nature of the response has provoked some sceptical response, but the researchers are calling for others to reproduce the work in order to verify it.

Even if our bodies retain an ancestral magnetism which responds to unusual reorientation of the Earth’s field, it may not be a signal we actually use.

The Earth’s field is extremely weak — amounting to less than 1 per cent of a normal fridge magnet, and only slightly stronger than the field around a magnetised bank card strip, meaning any sensitivity is likely to be easily disrupted.
 
A research team in 2014 showed that electrical goods and radio waves of a modern city do create enough noise to disorientate robins, which normally navigate using Earth’s magnetic field. But even the strongest magnets in daily life, MRI machines, with a magnetic power 1,000 times stronger than a good fridge magnet, don’t register to us beyond the noise of the machinery.

And they almost certainly don’t do us any harm at all: magnets even stronger were used to levitate a small frog, and won researchers an Ig Nobel prize for letting the frog hop away unharmed.
 
The power and mystery of magnetic fields remains compelling, whether we can sense them or not.