We've had a fair number of chats about this on the site before, actually Joel and I talked about the whole lack of fossil fuels option about a month ago, and it pretty much ends on the same thought as it has for decades now. See, we've refined and solidified a lot of data but we've known for a long time that there were billions of star sin our galaxy, billions of galaxies, and that G type stars (which are not the only candidates for intelligent life) would doubtless numbers at least millions in our own galaxy with at least 1% surely having planets and surely at least 1 in 10 having Earth-ish-sized planets in the 'goldilocks zone' with water on them. So we couldn't imagine how there'd be anything less than at least 1000 Earth-ish worlds just in our galaxy, on the extremely low, low end, with millions or even billions of them quite probably, and billions times that in the Observable Universe close enough that life could have formed and got a signal off just in case we were a freak galaxy or something.

And yet, Great Big Silence, I pretty much fall into the camp that assumes Occam's Razor slices us to "Advanced Technological Life is absurdly rare compared to life" and that even multi-cellular life is probable pretty uncommon.