Actually, we do have ways of being sure, the same ways that counter, for most people, the world-wide flood. Things that happen to the Earth leave traces in the geological record. And there aren't any. And if in periods when traditions could record them, in histories such as those of the Chinese, which go back a long way, and are very careful to be accurate. Again, nothing.

It isn't a theory - theories are things which can be, and have been, tested and are supported by evidence. It may be a hypothesis, but probably not, as those need to be based on observations.

And it needs a mechanism, a way in whch it could be done. It was the absence of a mechanism whch led to the delays in accepting continental drift/plate tectonics so long. The mechanism needs to take account of the size of the objects and forces involved.

Penny