Rare Earth Part I

Ah, science. What can we say about science?

Is the Earth rare (as opposed to well done, or raw?)?

Good question. Maybe.

Why does it matter? Well, there are several contrasting issues at stake. One is whether we are truly special; on a superficial level this is just the usual creative tension between the Anthropic Principle and the Principle of Mediocrity (the generalized Copernican Principle).
At another level, if we're really special, we should be careful - that is to say if life is rare, and intelligent life more so, then its existence is all the more precious (this leads naturally to an extreme environmentalist position centered on some sort of a precautionary principle). But, if we're not really special, but rather as common as dirt, should we not be careful and blithely accept extinction as really no big deal, I don't think so.
At yet another level, Rare Earth proponents move into blatant Deism, notably Guillermo Gonzalez, one of the original Rare Earth proponents who has expounded on this in a new book, Privileged Planet. This leads straight to an argument for Design, which inevitable falls for the usual fallacies of the Blind Watchmaker analogies (some of the stuff on, for example, origins.org, is just embarrassingly bad).
And, inevitably as the web goes, there is dedicated blogspot to combating this notion . Oh my. Fun read though.

So, is the Earth Really Rare. Well, yes, sorta maybe not really.
Hm, this is going to take a while.

In the meantime, one contemplates in turn the Drake Equation, which I remind you is an order of magnitude estimator for The Expected Number of Currently Existing Communicating Technological Civilizations in This Galaxy. Not of course to be confused with the extremely useful Date Equation (C. Kobulnicky et al sometime a few years ago).

To cut a long story short, given our current knowledge, it is hard to push the Drake Equation output to a value much smaller than 1 (ie low probability of even one civilization in existence at any given time). So, we get the Fermi paradox, of "where are they". This is subtler than it sounds.

To seriously consider what is going on, we need to contemplate the Habitable Zone, the Continuously Habitable Zone and the not-quite-so-respectable Galactic Habitable Zone (and can we please stop there, no more Zones unless they involve Vingean singularities and actual engineering).

To be continued...