Life seeded throughout the cosmos makes for a satisfying vision, but what are the odds that some kind of panspermia could really happen? Rutgers researchers cast a bit of cold water on the concept recently with data showing what happens to DNA from microbes frozen for millions of years in Antarctic ice. The upshot: Radiation bombardment in the interstellar depths makes survival unlikely. That makes the Fred Hoyle-style delivery of life via cometary bombardment look improbable.
Antartica makes a good testbed for such studies because the polar regions receive more cosmic radiation than anywhere else on the planet, as well as containing its oldest ices. The DNA in the five samples studied by the research team showed marked decline after 1.1 million years. Rutgers’ Kay Bidle notes that “There is still DNA left after 1.1 million years. But 1.1 million years is the ‘half-life’ – that is, every 1.1 million years, the DNA gets chopped in half.”
Bidle’s team doesn’t completely rule out life being transferred among planets within the Solar System, but finds it unlikely that life on Earth could have arisen from extrasolar sources. Somewhat lost in the shuffle is the impressive news that DNA frozen in glaciers may return to life with glacial melting even after vast periods of time. The team sampled and melted ices ranging from 100,000 to eight million years old looking for microorganisms that had been trapped within.
And find them they did. As expected, the microorganisms from younger ice grew more quickly than their older counterparts. And those in the oldest ice couldn’t be identified at all because of the deterioration in DNA. The ices came from two valleys in the Transantarctic Mountains, a remote and hostile place that reminds us of the incessant mutability of living things, something to be kept in mind as we ponder potential habitats on other planets both in our system and beyond.
The paper is Bidle, “Fossil genes and microbes in the oldest ice on Earth,” published online on August 8 by Proceedings of the National Academy of Sciences (abstract). I’ll post the print reference when it becomes available.