By ‘aliens’ the writer of this article is talking about a species that has evolved independently of known life.
The basic idea is this:
Nonlife can turn into life.
If life can appear on earth once then there’s no reason that it can’t have happened twice, or still be happpening all around us.
If we can prove it’s happened twice, that tells us that it’s a relatively common event (on an astronomical scale).
If the beginning of life is a common occurence then that significantly increases the chances that it has happened in many other places.
… But first we have to find life that hasn’t descended from the same ancestor as all of the rest of us!
This little article is about the search for life that is descended from a fresh ancestor – life with which we have no common living ancestry. ALIENS! Click here to read it!