Comet!

Oh NO!!! RUN!! The sky is falling! (or so says Chicken Little)

I think this is a bit misleading. The ancients had very little knowledge of things not of the Earth, and probably didn't know the difference between a comet and an asteroid. I think we should call this threat a "near earth object", as that will encompass any dangerous object coming from space.

Some of the prophecies talk about such objects entering Earth's atmosphere and striking the surface. The Bible, the Bible Codes and others either state directly (Comets, large rocks, etc.) or hint at this, making it more probable.

Such events can be rather devastating, depending on the size of the object and where it hits. It is unfortunate that we have no data in this regard.

It is likely that the object will be a Comet, rather than an asteroid since the movements and orbits of most asteroids is known. A Comet on the other hand can be a rather unpredictable object and could appear suddenly, leaving little time to prepare.

This kind of event would be planet changing, though, not necessarily extinction level.