I had always been taught the first explination. But when I used that in a reply to someone's question, was told that I was wrong and that the combustion was actually caused by the second explination. Since these two ideas are at odds, I think maybe i'll just say it's some huge government/NASA coverup and that it's actually being shot by an alien defense lazer beam they set up to save us from unhealthily large meteor impacts. (not all aliens want to kill us, duh).
okay but seriously, which statement above is correct? or is it like so many other things, and it's a little of each?