...the giant crater that suddenly appeared in Siberia was not a crashed alien spaceship. We know that because we know it wasn't caused by something hitting out of the sky (like, say, a meteorite).
What caused it? It was probably a very large gas explosion. Gas extraction is taking place not that far from the area - for those who don't know, it's the Russian peninsular of Yamal, literally called "The Ends of the Earth" by its original inhabitants. A bit of melting of the permafrost in areas where methane is close to the surface can cause explosions. This one is just unusually large. Scientists aren't entirely sure exactly what caused it, but it definitely seems to have happened from below. Thus, it's closer to a sinkhole than a crater.
(Apparently some people are blaming ET. Nope. I wish that was remotely possible, but nope.)