Thanks for your comments. The 2012 myth is, itself a myth. In other words, this entire hoopla is based on quite literally nothing–a myth about a myth. If I understand correctly, and I have done some research into it, the entire hype is built on the fact that one particular Mayan calander comes to the "end of the world" in 2012. The best I can tell, the Mayans themselves did not see this as a big event, or if they did, we have no evidence that they did. Their cosmology, as with so many other ancient cultures and religions such as the Buddhists, Hindus and Jains, is cyclical. In other words, they see history and cosmology as following a repeating pattern of death and rebirth. If 2012 is anything for the Mayans, it is the turning of the calendar to a new cycle. It is not the end of the world in the sense that a linear view of the world and time would see it, but is as much a new beginning as an end. The best I can tell from looking into the so-called 2012 prophecy is that there is no catastrophe foreseen. So much for any kind of apocalyptic view.
Let us suppose for a minute that the Mayans really did see 2012 as the end of a cycle. I do not at all concede that this is true, but only that one particular calendar saw it that way. The next reasonable question is whether any reasonable person would see this as having some basis in reality. I would say that the only ones who will take this at all seriously are either extremely gullible people or ones who hope to make big bucks on the gullible. A number of New Agers have taken up the gauntlet–making this into some sort of symbolically significant thing–the beginning of a new era of peace and happiness. This tells us a lot about how credulous such New-Agers are. Such people care rather little about truth, but will use anything, no matter how blatantly bogus, to push their Westernized Hindu world view. One can only hope that reasonable people will take this blatant abuse of common sense as sufficient reason to reject New Age thinking.
About predictions of a catastrophic asteroid collisions with the earth, from my perspective this is a scientific question, not something to be determined by some sort of apocalyptic Mayan calendar or anything else. The earth has been struck by large objects in the past. For example, there is compelling evidence that the Chixlub asteroid hit the earth at the northwest corner of the Yucatan Peninsula 65 million years ago with catastrophic effects, including probably putting an end to the dinosaurs. There is also the Tunguska Meteorite which struck in Siberia in 1908. Actually, scientists believe it was a meteorite which did not strike the ground but broke up above the earth, releasing an amount of energy many times greater than the explosions in Hiroshima and Nagasaki. It is estimated that this object was several meters across. If it had happened over a populated area many would have died.
Massive, catastrophic meteor/asteroid strikes are extremely rare events which are governed by statistics and physics. There are a number of objects in our solar system which occasionally have relatively near collisions with the earth. "Near" is a relative thing, as on a the scale of our solar system coming within one million miles of the earth would be a near collision. Some have proposed that governments ought to prepare for the possibility of an asteroid strike by building a satellite which could deflect such an asteroid from hitting the earth. The dates you have listed above (2029/2036) are dates when scientists have predicted near collisions. Do not worry yourself, the likelihood of one of these actually striking the earth on these dates is truly miniscule.
How should a Christian respond to such nonsense? Probably we should pretty much ignore it, but perhaps we can turn a conversation or two from the blatantly bogus nature of the 2012 hope to the overwhelming evidence for the resurrection of Jesus and the inspiration of the Bible.