Four times in the last few years, scientists have announced finding planets orbiting other stars in the "sweet spot habitable zone" -- not too hot, not too cold -- where water and perhaps life are possible. Sooner rather than later, it is speculated, there will be discovered a "lukewarm planet with a size making it probably Earthlike." This brings up the usual cautionary notes:
Microbes can spring up anywhere that is wet and warm, astronomers say, although biologists are not so sanguine. But the emergence of large creatures, let alone intelligent ones, as evidenced by the history of the Earth, depends on a chain of events and accidents — from asteroid strikes to plate tectonics — that are unlikely to be repeated anytime soon. “If you reran Earth's history, how many times would you get animals?” asked Donald Brownlee, an astronomer at the University of Washington. He and a colleague, the paleontologist Peter Ward, made a case that we live on a lucky planet in their 1999 book, “Rare Earth.”
Single-cell life might be common, given the right simple conditions, explained Dr. Marcy in an e-mail. “But the steady, long-term evolution toward critters that play improv saxophone, write alliteration poems, and build heavy-lifting rocket boosters may depend on a prohibitive list of planetary prerequisites,” he added.
A rather Earthocentric view, so to speak. We think life might be improbable elsewhere because we know only about life here. And if a series of "unlikely accidents" happened in one place, it can't happen (perhaps in a slightly different way) on one of the vast number of planets out there? I'm afraid I'm an incurable romantic when it comes to life elsewhere in the universe. The alternative is too depressing. And before you bring in the religious angle, the idea that an omnipotent God with all of eternity and infinity to play with would be satisfied with this one tiny little lab experiment is even more depressing.
