Amanda Angelika wrote:

In a way. But "belief" suggests something supernatural which is wholly
reliant on faith.

No. While 'supernatural' requires belief because it isn't 'naturally
occuring', the reverse is not true.  I can believe that cavemen reached
the south pole, or that vikings sailed to china, neither of which is
'supernatural'.

 The idea that aliens have been visiting the Earth is a
theory based on scientific evidence and the possibilities it presents. E.g
our knowledge of the Universe itself and awareness of the laws of physics.

You mix up 'have' and 'possibly'. Even if it were possible, that does
not imply that it has happened, ever.

It's also based on anecdotal evidence, witness testimony and to some extent
even physical evidence.

There is anecdotal 'evidence' that Thor makes the thunder and
lightning.

In order to remain sceptical in the face of such evidence, means one has to
maintain an idea that all the evidence is totally worthless.

No. Only that it is not convincing. It is possible, as you say, but
possible does not mean that it has happened.

However in
order to do that one has to have an alternative theory, belief or a
particular view of the Nature of the Universe. So until there is conclusive
evidence one way or another it's all a matter of conjecture and belief.

There yer go, you do agree that it is a matter of conjecture and
belief.

But at the end of the day there is more evidence supporting the possibility
than there is of the impossibility. So IMO it is more rational to base ones
theories on possibility because the alternative is impossible.

It's possible that a volcano may errupt under my house, but it would be
irrational to base my actions on this happening in the next five
minutes.