Earth relies on its magnetic shield for protection

Photo: earth.com

Earth's magnetic shield protects against harmful effects of the Sun.

Our planet is surrounded by a magnetic field that acts as a shield.

It keeps the solar wind away from the top of our atmosphere, preventing it from scrubbing our atmosphere away, and reduces the consequences for us of the Sun's bad behaviour. This magnetic shield is generated by electric currents flowing in our planet's liquid interior.

Mars is an example of what happens when that magnetic field disappears. Being a smaller world, it cooled faster and its interior solidified. The electric currents ceased to be generated and the magnetic field largely vanished, allowing the solar wind to start scrubbing away at the atmosphere.

Today, Mars' surface is a frigid, almost airless desert. Our planet is much larger than Mars, and therefore cooling more slowly, so solidification of its interior lies a long way off. However, recent research suggests a situation that is more complicated.

In the 1960s, magnetometers—devices for measuring the strength and direction of magnetic fields—became sensitive enough to measure the magnetic fields of rocks on the beds of the oceans. Scientists found, particularly in the case of the Atlantic, something really interesting. There were bands of rock of alternating magnetic polarity, showing the Earth's magnetic field has reversed over and over again through history, with the pattern mirror imaged around the Central Atlantic Ridge.

The Atlantic seabed is split at the ridge, with lava coming up forming new seabed. As it cooled, it "remembered" the Earth's magnetic field at the time it solidified. Evidence of these magnetic field reversals has been found all over the world. There have been at least 183 reversals over the last 83 million years. They are global, not local, events.

One consequence of these magnetic field reversals is that for a time in each cycle, the Earth's magnetic field is zero, for thousands of years, allowing the solar wind and other space weather phenomena to plough right into our atmosphere. Looking at the situation on Mars, what did it mean for life on Earth? What has been the impact of these reversals? Reassuringly, the impacts, if any, were slight. One of these periods of zero magnetic field occurred some 750,000 years ago. For maybe as long as 10,000 years, the Earth had no magnetic field. Our planet was teeming with life at the time and our ancestors were prowling around in Africa and elsewhere. They survived. How would we deal with a magnetic field reversal now?

Some scientists have suggested the changes now taking place in the Earth's magnetic field are leading to a reversal event. Others say the magnetic field varies slightly all the time and what we see now is just one of these random variations. At some point we will know which it is.

Magnetic field reversals must have happened many times since life appeared on Earth around 3.5 billion years ago and it is still abundant. However, what might require more consideration is the technical environment we have built for ourselves.

We know that space weather, driven by the Sun's behaviour can severely affect our technical infrastructure (power, communications, transportation etc.), and without the protection of our shielding magnetosphere, some space weather events could produce far more disruption.

We are, however, learning more and more about how solar behaviour affects our technology, and how to mitigate those effects. Canada and other nations are keeping a close eye on the Sun's behaviour and how our planet and technical systems respond to it. Since we know that at some point we will get another magnetic field reversal, we have no excuse for not being ready for it.

•••

• Venus and Saturn lie close together low in the southeast before dawn.

• Jupiter is low in the west after sunset, with Mars higher, in the southwest.

• The Moon will reach its last quarter on the May 20.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.