The earth has two North poles, the geographic and the magnetic. The magnetic pole is the one that attracts the needles of our compasses and it’s always moving. Science has taught us that the magnetic pole flips from north to south every 250,000 years. Since the planet is now more than 500,000 years overdue for its next inversion, we could be on the eve of such a major event. What would be the impact? Would the Earth's magnetic field still protect us from solar winds and cosmic rays?

In this excellent program for Earth and Space Science, The Nature of Things talks to geophysicists, geologists, astronauts, marine biologists and paleomagneticians in an attempt to understand pole reversal.