Complex life in only 10% of all galaxies?

[Ann]

Yesterday, Swedish newspapers reported that life might be possible only in 10% of all galaxies. Well, newspapers are not the best place to look for accurate astronomy news, so I had to look it up myself. The source is a paper by Tsvi Piran at the Hebrew University of Jerusalem and Raul Jimenez at the University of Barcelona in Spain. According to a summary of their conclusions by Adrian Cho, the sterilizing culprit would be the long gamma-ray bursts.

Using the average metallicity and the rough distribution of stars in our Milky Way galaxy, Piran and Jimenez estimate the rates for long and short bursts across the galaxy. They find that the more-energetic long bursts are the real killers and that the chance Earth has been exposed to a lethal blast in the past billion years is about 50%. Some astrophysicists have suggested a gamma ray burst may have caused the Ordovician extinction, a global cataclysm about 450 million years ago that wiped out 80% of Earth's species, Piran notes.

Things are even bleaker in other galaxies, the researchers report. Compared with the Milky Way, most galaxies are small and low in metallicity. As a result, 90% of them should have too many long gamma ray bursts to sustain life, they argue. What’s more, for about 5 billion years after the big bang, all galaxies were like that, so long gamma ray bursts would have made life impossible anywhere.

How likely is it that gamma-ray bursts would kill off even all bacterial life, then? Not likely, says Brian Thomas, a physicist at Washburn University in Topeka.

But are 90% of the galaxies barren? That may be going too far, Thomas says. The radiation exposures Piran and Jimenez talk about would do great damage, but they likely wouldn't snuff out every microbe, he contends. "Completely wiping out life?" he says. "Maybe not."

But Piran says that the gamma-ray bursts would kill off the life that we humans are interested in:

"It's almost certain that bacteria and lower forms of life could survive such an event," he acknowledges. "But [for more complex life] it would be like hitting a reset button. You'd have to start over from scratch."

So what are your thoughts about this, folks? Any comments from you?

Ann

[rstevenson]

Evolution is seemingly a powerful force. I wonder if such stress could ever produce life forms that could resist major damage from Gamma rays? Think of crabs, shellfish, and so on. How thick would their covering need to be, and of what materials, to protect individuals during a gamma ray burst? Can an organism extract lead from its surroundings and build a shell using it? Could a whole ecosystem develop that way? Maybe deep underground or in deep oceans?

Rob

[Chris Peterson]

Evolution is seemingly a powerful force. I wonder if such stress could ever produce life forms that could resist major damage from Gamma rays? Think of crabs, shellfish, and so on. How thick would their covering need to be, and of what materials, to protect individuals during a gamma ray burst? Can an organism extract lead from its surroundings and build a shell using it? Could a whole ecosystem develop that way? Maybe deep underground or in deep oceans?

I would think a robust repair mechanism for DNA (or the equivalent molecular carrier of genetic information) would be a much better strategy than some sort of biological shielding. Of course, simply being underwater (even very shallow) or below the ground would be effective, too.

[geckzilla]

The water would protect them from high energy particles very well but I think somehow the ocean could become uninhabitable in another way if the atmosphere is significantly modified by gamma ray bursts in such a way that the eventual result is either a Mars or a Venus type scenario.