It is separate, with regards to life, as far as we can tell.
Originally Posted by Colin Robinson
No we don't. It means we think of the earth as not favored or unique, not that we think that it's like everything else. That's not incompatible with the idea that the conditions for life are uncommon enough that we'll never find it elsewhere. the Copernican Principle is about how we view probability, but has no bearing on the physical reality that determines probability.
Today, thanks to Copernicus we think of the Earth as a planet comparable to other planets. And yet, many relics of pre-Copernican thinking remain in the way we talk about the universe.
Provincialism is provincial, and semantics is semantic. We use articles with it because earth can have different meanings in normal conversation. The moon is often referred to that way because we use the word generically instead of using a proper name for it in common conversation. you may notice that sometimes people don't capitilize earth or moon unless its used without an article.
For instance, the very fact that we speak of "the Earth" is based on the old idea that Earth is an object in a class of its own. We don't speak of "the Mars" or "the Jupiter".
On the contrary, Ganymede is "a moon" and Sirius is "a sun" for bodies in its system.
We do speak of "the Moon" and "the Sun", but only because each of these bodies looks unique when viewed from Earth. We don't speak of "the Ganymede" or "the Sirius".
Geographic features are characteristics of extra-terrestrial objects, not extra-terrestrial objects on their own. One of these things is not like the others.
The term "extra-terrestrial" -- as in "extra-terrestrial life" -- is based on the same old idea, that Earth is in a class of its own. We might as well speak of the highlands of the Moon as "extra-terrestrial mountains", or the lakes of Titan as "exo-lakes".
IIRC, the moon does have life on it that we put there.
We know a little more than we did in the days of Kepler, when it was thought that the Moon might have life on it.
Et tu BAUT? Quantum mutatus ab illo.