Question

what makes the earth behave like a magnet

Answer 1

i believe it has to do with the poles. The poles act as a magnetic field. i am not completely sure, but i think that is right.

Answer 2

check the movie called 'The Core'

Answer 3

for magnetic field you need moving charge, I am not sure but some layer in earth like mantle may have ions (charged) and moving around axis through poles..