h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I was watching the discovery channel today and learned something quite startling.

It seems that the solar wind is what stripped the planet Mercury of whatever atmosphere it may have once had and it is slowly but surely stripping Venus of its thick and poisonous atmosphere.

And, it turns out, that the only reason the Earth's atmosphere hasn't being stripped away is because we are the only inner planet with a magnetic field that extends past our atmosphere and is thus strong enough to fight off the destructive power of the solar winds. It turns out the Northern lights are a life-saving battle between the sun and Earth.

It now seems even more incredible to me that life exists here at all - first we're at the right distance for the temperatures to be not too extreme, then we have liquid water and now I find out that if we didn't have this huge magnetic field, our atmosphere would now be as thin as the Martian atmosphere.

It now seems to me that terraforming some worlds will not be possible unless you can first create artificial magnetic field large enough to protect the atmosphere from being stripped away as it is being processed.