Or if the Earths magnetic field disappeared which could only happen if the earth stopped rotating which is impossible as long as their is still a gravitational field of influence.
There has been some reports that our polar magnetism is shifting, thus weakening it enough so that if a solar flare or any other such outer-space activity stuck us, all life on earth would dissapear. Solar flares are made of pure gamma radiation. You would need many, many tons of lead to block even a small amount of gamma radiation.
In a few years, North will be South, due to the shifting poles. This is scientifically predicted to be around 3 or 4 years from now.
Now, I believe the reason for the shifts is because both poles need to rest. After all, nothing has limitless energy.
Anyway, The Myan calender had 5 catistropic events on its dates. 4 have actually happened. Each has been enough to reduce the life on earth by an extreamly noticable anount. Each date has been checked, and it was confermed that they each happened on the written date.
Of coutse, this does not prove anything. The Myans were absolutely obssesed with time, so perhaps they didn't have tme to waste on extending the calender.