well, ok here's what I don't get about these 'earth like' and 'habitable' concepts. These are only valid for living organisms that are located on earth right now, the universe is pretty massive I don't think referencing a tiny piece of planet when looking at this massive almost endless space would be accurate. All they're looking for is carbon based life forms that require o2 and water but what if there are organisms out there that are completely different to what we have in our frame of mind? I mean a tardigrade could potentially survive in space with no atmosphere or any resources, in fact NASA was so scared of contamination that they've decided to launch Galileo spacecraft into Jupiter's atmosphere and burn it down to little bits.
There is a good chance that we are not alone in this universe, but there is also a good chance that we will never meet any of them in our time frame. The observable universe is stretched out to 13.8 billion years, even if a life form advanced enough, somehow figures out to send radio waves into the space, and are decrypt-able by our technology and somehow the waves coincidentally encountered by us in the last 100 years which is equivalent to 0.00000725% of the age of the universe.
Yeah.. you decide from this point.
edit: and think of this humans only started listening to radiowaves from space consciously after 1964.