If Mayan prophecy is true, just how will it all end on Friday? Scientists foretell the cataclysms that could bring on Doomsday...
They say it won't happen, at least not on Friday, but in the event the Mayan prophecy of the end of the world is right, scientists have foretold a raft of bloody and catastrophic fates for us all.
Dark comets, famine, super-volcanoes, catastrophic climate change, and a plague of cancers are just some of the ends that could fulfill the prophecy.
Astrophysicist Professor Jocelyn Bell Burnell, who discovered pulsars, believes the most likely disaster that could pencil Doomsday into Friday's diary is a black comet.
Such an end would match that of the dinosaurs who after walking the planet for about 165 million years - homo sapiens has been around for a mere 200,000 years - were killed off by a 10km asteroid or comet that slammed into the planet.
Professor Bell Burnell believes if the world as we know it is to end on December 21 it would have to be a dark comet that strikes.
Dark comets have little of the ice and snow that most comets have, and a lot more dust which makes it much more difficult to spot them as they speed through Space.
'Comets normally are big, dusty snowballs. A dark comet has not much snow and a lot of dust. They are much harder to get a handle on,' she said.
The collision itself, except for those near the point of impact, would be unlikely to be fatal to the world's population but it would throw up so much dust into the atmosphere that billions of people could expect a slow death.
Huge quantities of dust would bring on an 'eternal winter' in which the sun would be obscured and crops around the world would fail, leading to mass famine.
Dr Dave Rothery, a volcanologist at the Open University, foretells a similar end but he thinks the death-bringing dust would be put into the atmosphere by a supervolcano.