EARTH'S MAGNETIC FIELD

-LIKE THAT OF A GIANT BAR MAGNET

-LINES OF FORCE SHOW DIRECTION COMPASS NEEDLE POINTS

-CANNOT BE FROM A PERMANANENT MAGNET BECAUSE THE CORE - WHERE THE FIELD ORIGINATES - IS TOO HOT

-INSTEAD IT ARISES FROM MOTION - THERMAL CONVECTION - OF HOT IRON FLUID IN OUTER CORE (AND THUS IS ONE OF THE REASONS WE THINK THE CORE IS MADE OF IRON)

-IT REVERSES AT TIMES (NORTH MAGNETIC POLE BECOMES SOUTH MAGNETIC POLE)

-BECAUSE ROCKS RECORD THE MAGNETIC FIELD IT GIVES US A WAY OF TELLING WHERE AND WHEN ROCKS FORMED