Saturday, November 13, 2010

Dead on Arrival

By now, we're all familiar with panspermia or more accurately exogenesis--the hypothetical scenario in which life was "deposited" onto Earth by some kind of asteroid or collision early on.

An argument occasionally arises against this idea, supposing that radiation would cause anything but the toughest extremophiles to be damaged beyond repair. There is the emerging idea that genetic material could still be recovered from damaged (read: dead) biological molecules and be used as a sort of springboard for life to develop.

Paul S. Wesson's new paper in Space Science Reviews talks about his theory of "necropanspermia", which isn't nearly as supernatural and awesome as it sounds, but it does bring up a lot of interesting questions about how life gets around in outer space, if it does at all.

Wesson encourages his peers to focus not on the question of "alive or dead" but "the question of genetic information". He argues that "random chemical interactions cannot produce the genetic information" present on Earth right now. He demonstrates by using a model of a prebiotic Earth with a given amount of amino acids. He then goes on to say that the "molecular interactions" that would follow would take 500x10^6 years to create 194 bits of information. For comparison, he gives e. coli: 6x10^6 bits, and a typical virus: 1.2x10^5 bits. So, he posits two possible conclusions. Either, life began on Earth under a directed, not random, sequence of chemical interactions, or it was a large amount of genetic information that was deposited here very early on. Wesson sides with the second camp. "Natural processes do not account for the genomes of observed organisms," he says.

He does, however, admit "that all versions of panspermia suffer from a hole in our knowledge, concerning how to go from an astrophysically-delivered entity which contains substantial information to one which has the characteristics of what we normally regard as life."

So his point is basically that viruses are great candidates to be used as a vessel for genetic information, since that's basically what they are.

One of the biggest detractors is Rocco Mancinelli, who quipped that "once you're dead, you're dead." He studies extremophiles for a living and what needs to go on in an environment to sustain life. I tend to agree with his take on the issue, as he points out that Wesson has missed a few drawbacks to his theory--essentially, that there are more dangers out there than he's led us on to.

Mancinelli mentions potassium decay (over the course of a long period of time in space: very damaging) and dessication, when hydrogen and hydroxyl molecules separate from the cells and form water, which serves to "denature" proteins, forcing them to recombine and lose functionality.



  1. I hadn't considered this view before with regard to panspermia. I guess it would make sense to at least consider the survival of the genetic material or organisms as a possible origin of life on Earth. When was this article written? Is it still considered to be a valid hypothesis today? I agree with you Nik in siding more with Manicenelli on this issue: it seems to me that with what we know about the complexity of the pre-biotic molecules, it wouldn't make sense for a molecule as complex, and intricate in structure as something like DNA to be one of the first molecules to habitat Earth...

  2. this is an interesting idea and would be pretty profound for astrobiology because what could we really understand about the origin or life if it didn't even originate here? maybe our life is habitable to life but not to the origin of life. what if planets that are habitable to life or not necessarily the same thing as those habitable to the origin or life?