Im not sure, however i know of big activites that go on Earth and take place every few hundred thousand years. Maybe this is the change of jugs or maybe not. The north and south poles switch. And about every 600,000 years this massive volcanoe erupts causing mass devastation (i think the volcanoe is 70km) And we are due to have this eruption, because 630,000 years have gone by.
Anyway im probably completly wrong so wait for other replies.