 The Mayans were very good astronomers. They knew how the planets moved, they knew about the seasons and they made very good calendars. Like us, they had cycles in their calendars. We have months, years, centuries. They had different cycles but they still had cycles and one of their cycles lasted over 5,000 years. And that cycle is coming to an end this year in December. Now the Mayans, as far as I can understand, reckoned that that was the end of a cycle and that there would be a new cycle following it, a rebirth. They did not reckon it was the end of everything. There are quite a few theories about how the world might end. For example, it's been suggested that there could be a big solar storm which would take the world out. Well, we get solar storms from time to time and they're a bit troublesome if you're an astronaut. Indeed, not to good news if you're an astronaut. But down here on earth we are protected by the earth's magnetosphere, the effects of magnetic field. And okay, solar storms can disturb that. They can produce currents in power lines that sometimes cause trouble. They can take out satellites, stop satellites working. So they could affect our GPS and any telephone calls that go by satellite, for example. But they're not going to end the world. Every so often asteroids do hit the earth. We know we can see some of the craters. There's Meteor crater or Barringer crater as it's properly called in Arizona. And there's traces of a very big crater partly on the Mexican Yucatan Peninsula and partly under the sea. That big crater was the result of an impact about 65 million years ago. And it's thought that's what caused the extinction of the dinosaurs and many other things. So a big thing like that could cause us some problems. Broadly speaking, what happens is when something big like that impacts, it not only makes a crater, it kicks up a whole lot of dust into the atmosphere. And the atmosphere cuts out the sunlight and that stops crops growing and foods fail and there's starvation and so on. So that is something we need to look out for. And we are looking out for. There's an array of telescopes all around the world monitoring the sky night after night. Actually monitoring about a thousand potentially hazardous objects. Things that might come and hit the earth one day. As they monitor them, they discover that the vast majority of them won't. But as they get the orbit more accurately, they see it'll miss the earth. But if there was something coming to hit the earth, we'd get two or three years notice. And even with today's technology, we could divert it so that it didn't impact the earth. And there's research going on all the time which will improve that technology so that it gets easier to divert an incoming asteroid. We've got no knowledge of any big asteroid coming to hit us. Some of the techniques they use to deflect an asteroid, one of them is to paint it white all over, which means it reflects sunlight very well. And the sunlight bouncing off the asteroid will push it sideways so that it'll move away and not hit the earth. That's one of the neatest solutions. But they're also developing what they call gravity tractors. Satellites that are pretty heavy and through their own gravity can attract the asteroid and make it change course. And there's also some that will actually physically hook onto the asteroid and tug it aside. So there's lots of ways of doing this. The magnetic field of the earth, the thing that makes your compass point due north, that flips over every so often. And I'm using flip as a geologist would use flip. The flip actually takes 5,000 years. We think what happens when a flip is coming up in a few thousand years is that the earth's magnetic field starts to shrink. It doesn't disappear completely but it shrinks. It then turns over. North becomes south and south becomes north and grows again. And at the moment it is true the earth's magnetic field is shrinking. But we've only been measuring the earth's magnetic field for about 200 years and we don't really have a very good database. It may meander around a bit anyway. Or it might be the beginning of a flip. But remembering it takes 5,000 years, it's not going to be accomplished before the end of 2012. In the last two or three million years since two losing people started appearing on earth, there have been about a dozen of these flips of the earth's magnetic field and it doesn't seem to have done anybody any harm. I do a lot of outreach lectures and starting several years ago, particularly in the USA, particularly lecturing to schools, regardless of what I was lecturing about, at the end some kid would put up their hand and say, is the world going to end in 2012? And after two or three questions like this I thought I'd better look into it. And that's where this whole exercise started for me.