2012.
It won't.
The whole scare is being caused by a bunch of religious nutcases; there is a part somewhere in the bible that talks about the coming events, almost every religion has it in their "book" actually. Things about something passing over the sky, and a second sun rising from the south, then hell breaks loose basically.
It's about a mini-star cluser, OR asteroid, OR comet (scientists aren't sure yet) which will PROBABLY pass into our solar system, December 21st, 2012. When that happens, there are 7 possible scenarios which can happen depending on where the asteroid (called Nibiru) comes in, then the gravitational pull between the asteroid and the sun will be LETHAL to anything inside it, or behind it.
The best possible scenario is that Earth is already ahead of the "kill zone" when Nibiru enters our atmosphere.
As for the Mayans, they were people beyond our reasoning; they had technologies we don't (look at the megaliths they've created, it's IMPOSSIBLE even for today's technology to pull that off), although their calendar ending is misunderstood. When their calendar "ends" on 2012, it isn't really ending, but starting into a new cycle, under Aquarius. This, however, means much expected water, if you take the element of it seriously. If you don't, then it simply means, there's a new cycle.
A new cycle to the Mayans meant something POSITIVE, not death and destruction to everybody. It's possible on 2012 that we'll see some sort of miracle, or greatly advance our technology, or who knows, maybe the aliens that every religion has written about (look it up) will come back, but at any rate, the Mayans never predicted anything such as a catastrophic event, or "doomsday".
The religions around the world have been freaking out only because of their insane "death to everybody" prophecies, the catholic religion in specific, so they've taken this atmospheric coincidence as an opportunity to convert everybody to their religion, to "save" them.
And by the way, if you look online, almost every article condoning death and misery in 2012 is backed by religious theory, and/or are trying to sell you some sort of book or item. Seriously, go look.
Furthermore, scientists are already keeping an eye on this "Nibiru", which religions believe is a "death star" (literally) which is coming back from past events, carrying giant humans (Nihiliants) which will destroy us all...unlikely.
There were (most likely) giant humans at one point in time on the Earth, but prehistoric conditions are REQUIRED for their survival. So even if they "hopped on" to this Nibiru, and flew away to safety, then coming back to Earth would be suicide for them. This is the same reason that Dinosaurs would not be able to strive on our Earth ever again, even if we found a way to bring them back.
Long story short, don't panic:
1) Mayan calendar isn't ending, but entering a new cycle.
2) Religions are blowing this way out of proportion, it's an asteroid which won't even hit us.
3) Scientists are watching for the EXISTENCE of this asteroid, it's only had 2 sightings so far, both of which are not backed by any sources. I wonder why.
4) Even if it's proven to be true, there's still the chance that it'll enter our solar system at a good time.
5) Due to Nibiru's expected size, we should be able to walk outside, look at the sky, and see this "second sun from the south". Do you see any dark flame coming towards us? I don't. Neither does anybody else. We were supposed to be able to see it with our bare eyes since 2007.
In short: DON'T WORRY! This had me in a panic for like 3 days until I actually found the right sources of information.