We haven't yet found a speck of evidence for biology on another world, so we have no objective way to judge whether life is a onetime fluke or a near-inevitable phenomenon.

We've accounted for 95 percent of all the stars in the Milky Way. The other 5 percent are big, bright stars - the kind that dominate the night sky, but are lamentably both rare and short-lived. If biology's your thing, you can forget those guys.

Planets that don't currently sport plate tectonics, such as Venus and Mars, are scarcely habitable. Tectonics might be a requirement of any world that aspires to a rich diversity of life.

If this is the only planet on which not only life, but intelligent life, has arisen, that would be very unusual.

This garden is your life. Of course, there are the occasional weeds—but more than anything, this garden is filled with so much life!

It's always a tough call deciding whether, as a scientist, you should argue publicly with the creationists. It's a dilemma that I encounter frequently in another subject area: Does it make sense to bandy words with someone from the UFO community?