China's scientists explain doomsday theories
Apocalypse explanations are poles apart from mainstream and stem from fears of unexplained
Every few hundred millennia, the earth undergoes a radical change that sees the planet's magnetic poles flip.
The reversal - which would cause all compasses to point "south" rather than what we currently consider north - is long overdue, and some doomsday theorists believe the switch could come on December 20 or 21, when the current cycle of the Mayan Long Count calendar ends after 5,125 years.
Some scientists are also concerned, but their worries stem largely from uncertainty about the polarity reversal rather than fears the end is nigh.
Professor Chen Gengxiong , a researcher with the Institute of Geology and Geophysics at the Chinese Academy of Sciences (CAS), noted that the last magnetic pole reversal happened about 780,000 years ago - or about two times as long as it normally takes, according to geologic records.
And concerns over the unclear timetable are magnified by the fact that the magnetic north pole has moved up by about 1,100 kilometres since the 1800s - a phenomenon that Chen said some geophysicists consider the start of the latest reversal.
It appears to be a gradual process, but a popular doomsday hypothesis posits that, if the reversal were to occur in a single day, all of humanity would be destroyed when the world stops spinning, or perhaps because the magnetic field would cease to protect people from deadly cosmic rays.