Flipping heck, is our magnetic field safe?

Lecturer in chemistry at the University of Huddersfield.
OUR sun is the giver of life and provides much of our energy.

Its glow heats the Earth’s surface to a comfortable temperature and its light is absorbed by plants and turned into chemical energy which is then used by animals.

Oil and coal which we use as fuels are the decayed remains of long dead plants and animals that once utilised and hence stored the Sun’s energy (so in a roundabout way, you could say that all cars are in fact solar powered).

But the Sun also has a dangerous side. It continually emits a stream of highly energetic charged particles into space — the solar wind.

Without protection from this stream of particles, living organisms would suffer terrible molecular damage after prolonged exposure and given long enough it would strip the Earth of its atmosphere.

The surface of the Earth is protected from this bombardment by its magnetic field. This field is created by the motion of the molten iron within the core of the planet.

The stream of charged particles of the solar wind interacts with the Earth’s magnetic field causing its path to be deflected safely around the planet.

But it also causes some of the particles to be funnelled and concentrated.

Some particles are concentrated in a belt of particle radiation named after its discoverer, van Allen (contrary to popular conspiracy mythology, these radiation belts were not strong enough to be lethal to the Apollo astronauts as they flew through them to get to the Moon), and streams of particles are also funnelled in towards the poles.

Here, the collision of these high-energy particles with molecules in the upper atmosphere creates the spectacular aurora borealis and aurora australis, the famous northern and southern lights.

But the Earth’s magnetic field is not constant and unchanging.

The magnetic north pole was first located among the frozen arctic islands of northern Canada in 1831 but when its location was determined again in 1904 it was found to have moved by some 50km. During the past century, the position of the pole has been found to wander by about 10km per year.

The strength of the field also varies and since the 19th century has weakened by approximately 10 per cent. But is this weakening something to worry about? Will it disappear altogether?

The fact is that the Earth’s magnetic field flips upside down, “north” becoming “south” and vice versa. The result would be that compasses would point in the opposite direction with the “north” end of the needle pointing to the geographical south pole.

The Earth’s magnetic field has flipped thousands of times in its history.

The evidence for this repeated reversal of the field comes from volcanic rocks.

Many minerals have magnetic properties. When these minerals are molten, then cool and solidify, the magnetic field of the minerals aligns with the magnetic field of the Earth at the time. From then on, the magnetic field of the mineral is locked acting as a record.

What puzzled geologists was that the magnetic field of some rocks is aligned the wrong way — opposing the current magnetic field of the Earth.

The best example of this evidence is held in the rock that forms the ocean floor.

Africa and Europe are getting farther away from the Americas due to continental drift. The slabs of rock that form these continents and the ocean floor float on the hot magma below and move apart forming a crack that runs down the centre of the Atlantic Ocean.

New rock forms from the molten magma as it rises in the middle and fills the gap. Over millions of years as the magnetic field has oscillated, the forming ocean floor records the changes resulting in a pattern of “stripes” of alternating magnetic alignment that are symmetrical either side of the crack.

The last flip of the field occurred some 780,000 years ago and seems to occur on average every 300,000 years.

It is therefore possible that the weakening field we are currently seeing is simply the precursor to another flip.

The exact cause of these reversals is not fully understood but appears to be perfectly natural. But is it dangerous?

Examination of the fossil record shows no signs of any correlation between field reversals and extinctions.

Simulations predict that during reversals the field never fully disappears but becomes very tangled and complicated with multiple “north” and “south” poles before realigning itself in the opposite direction. So the Earth will remain protected.

Unfortunately, these flips take a few thousand years to occur and so we are somewhat unlikely to be able to appreciate the novelty of looking at a compass pointing “south”.