Aliens created us?

Current scientific theory postulates that life on Earth was made possible by comets that brought us the building blocks of life, namely the organic molecules that are present in all life here. The spacecraft that recently landed on the comet found traces of just such molecules. So I guess we could say it is likely that life on Earth came from outer space.

But created by space aliens in flying saucers or the like? I have seen no credible evidence to support such a theory, just a lot of unsubstantiated conjectures.

It is possible, in fact highly probable, that there is Life on other planets. But that does not mean it might be Life as it is on this planet of ours! There are many factors for the animal and plant life on this planet, not least of them water, carbon, and oxygen.