Why Living on a Giant Magnet is a Good Thing

One of the many things that is special about our planet is that we have a magnetic field surrounding it. On the face of it this doesn't sound so remarkable. So what? We can use a compass. Well, yes, but it is also one of the many factors that stopped us being a lifeless lump of rock floating through the endless, cold, uncaring void of space; it allowed us to be a living lump of rock floating through the endless, cold, uncaring void of space.

You may have heard of the solar wind, this is the stream of highly energetic particles released by the sun as it fuses hydrogen atoms together giving us our heat and light. But these particles could also wreak a terrible havoc if left unchecked. They're more than capable of stripping away our atmosphere and all the water on the planet without which there would be no life here, probably not even microbial life. Luckily for us many of the particles being churned out by the sun have a charge and can therefore be safely deflected by a magnetic field. Sometimes these particles get funnelled along the field to the poles of the planet where they can interact with the oxygen and nitrogen in our atmosphere, this is what produces the auroras borealis and australis. 

Our magnetic field, also known as the magnetosphere, is a result of the molten iron outer core of the planet, it slowly rotates and acts just like a giant bar magnet in the centre of the world. It is thought that Mars used to have such an iron core protecting it from the solar wind too, but Mars is only half our size and its core wasn't able to maintain its heat and so solidified a couple of billion years ago. It's quite possible that until then there had been good conditions for life on Mars, but with the protective shield gone conditions became ever more harsh and it is now unlikely that any life survives on Mars (although we should definitely go there and double check).

And so to the point. A new article in Science has pushed back the age of our magnetic field by some half a billion years to approximately 4 billion years ago. This is important because it has implications not just for understanding the geology of the planet but also for understanding how life on earth involved.

The work involved digging up samples of some of the oldest known rocks on earth in the Jack Hills of Australia. These rocks have remained almost completely unchanged for many billions of years. Analysis of the magnetically aligned zircon crystals within the rocks can reveal whether or not those rocks were formed at a time when the magnetic field was in place. And so it proved to be in these 4 billion year old samples. This older age of our magnetic field means that there may have been conditions favourable for life here on earth much earlier than previously thought. Given that bacteria and archaea don't tend to fossilise well, and that there aren't many examples of rocks that are as old as that, this could be an important piece of information in putting a date on when life might have begun.