Van Allen.
William Gilbert discovered the earths magnetic field!
For one, it helps block projectiles and keep some from getting to our atmosphere. It also holds the moon in place. And the last thing I can think of at the moment is that it helps us determine...
As stated in Wikipedia: "The last reversal was the Brunhes-Matuyama reversal approximately 780,000 years ago."
yea. ahh hun you know what it is... black and yellow>