How does the aurora borealis show weakness in the earth's magnetic field?

Such a protective magnetic field is viewed as essential for life on a planet, be it in our solar system or beyond.

But a magnetic field does not a habitable planet make. Mercury has a weak magnetic field and is certainly not habitable. Mars also once had a strong magnetic field and still has some remnants on its surface. But it fell apart early in the planet's life, and that may well have put a halt to the emergence or evolution of living things on the otherwise habitable planet.

I will return to some of the features of the northern lights and the magnetism is makes visible, but this is also an opportunity to explore the role of magnetism in biology itself.

This was a quasi-science for some time, but more recently it has been established that migrating birds and fish use magnetic sensors (in their beaks or noses, perhaps) to navigate northerly and southward paths. It has been known for some time that the lights are caused by reactions between the high-energy particles of solar flares colliding in the upper regions of our atmosphere and then descending along the lines of the planet's magnetic fields. Green lights tell of oxygen being struck at a certain altitude, red or blue of nitrogen.

But the patterns - sometimes broad, sometimes spectral, sometimes curled and sometimes columnar - are the result of the magnetic field that surrounds the planet. The energy travels along the many lines of that field, and lights them up to make our magnetic blanket visible.