Tuesday, March 11, 2014

Extraterrestrial origins of life: more than science fiction?


I am never opposed to a wacky idea just because it seems a bit "out there."  As such, I've always been open to the idea of panspermia, or the idea that life exists throughout the universe, and that life on Earth comes from an extraterrestrial origin.  Star Trek did it.  And Star Trek has been right about A LOT of things.  But joking aside, I like the idea of non-terrestrial origins of life.  We already accept the fact that the water on Earth came from space.  Is it so far-fetched to think that maybe life did too?

Not long ago, I came across an article on cracked.com, that made fun of scientists for believing in really wacky, non-sciency ideas.  Dr. Francis Crick (of Watson and Crick, the "discoverers" of the structure of DNA) apparently believed in panspermia. The author of the article, who completely misunderstands the idea behind panspermia and extraterrestrial origins of life, pokes fun at Crick for being as crazy as a scientologist.  Well, I'm here to challenge him.

Panspermia is not that crazy an idea.  Let me first summarize the arguments of Wickramasinghe and Trevors.  These guys first state that any paradigm shifting idea in science receives a lot of push-back from the scientific community, but the very process of challenging existing ideas is what science is all about.  The prevailing concept is that of a terrestrial "primordial soup" as the origin of life on Earth.  This idea states that all of the organic molecules that are life's chemical building blocks were originally formed entirely in terrestrial clouds through UV radiation from the sun and electrical discharges from lightening.  This has been replicated in laboratory work.  But what's lacking from this idea is how did life arise from the soup of organic compounds?  How did this system of amino acids and sugars develop into a self-replicating living cell?  Even without answering that, the primordial soup concept has achieved paradigm status, and is the predominant idea most people have on the origins of life on Earth.  This idea was challenged in the early 1900s, by Svante Arrhenius, who posited that bacterial spores containing genetic information could have been lifted off other planets and been propelled through space to Earth.  This idea was unpopular because it was untestable, because he basically said that the movement of extraterrestrial cells to Earth at the present time would be too small to be detected.  So the primordial soup idea remained as the favoured paradigm.

In the 1950s, the consensus among astronomers was that the dark irregular patches in the Milky Way were the result of ice particles.  But Wickramasinghe challenged this idea in the 1960s, showing that these "dust" particles were actually made of carbon, which is, of course, the signature element of life.  In characterizing this dust, he received a lot of criticism from both astronomers and biologists because this was a hugely paradigm-shifting idea.  In the 1980s, Wickramasinghe and his co-author Hoyle estimated that the random assembly of the simple amino acids and sugars in the primordial soup into even the simplest of self-replicating microbes involved probabilities so incredibly, infinitesimally small that they would not reasonably be thought to have happened in the context of the primordial soup in that amount of time.  Instead, they have posited a hypothesis that microbial life arrived on Earth around 4 billion years ago, which coincides with the an epoch of intense bombardment of the developing Earth.  This isn't so hard to imagine when we think about the discoveries of extremophilic microbes that can fit into every conceivable environment, no matter how inhospitable they might appear.

For example, waterbears (Tardigrades):
These guys are a micro-animal that can withstand temperatures at just around absolute zero (-273 Celsius, -460 Fahrenheit) and pressures about six times higher than what we would find in the deepest trenches of the ocean, AND ionizing radiation at doses hundreds of times higher than the lethal human dose, AND the vacuum of space.  Why would it need to have these traits if it was not exposed to these stressors regularly on Earth?  That doesn't seem to fit with the idea of evolution through natural selection, since there would be no suitable selective pressures for these traits on Earth.  Hmmmmm.

Then there's the Cyanobacteria:

These guys made the news last year for surviving over 550 days in space.  These little blue-green guys photosynthesize, just like plants do.  They hitched a ride on the outside of the International Space Station for 553 days, and survived!  In the cold vacuum of space.  If you're interested in learning more about Cyanobacteria, click here.

Other types of microbes have been taken into space and survived.  That's a pretty big deal!  So is it really that crazy to think that life on Earth might have originated in space?  The only way we'll ever be able to find out for sure if the origin of life on Earth is extraterrestrial is to find life out there, or traces of life, that has the same genetic code as terrestrial life.  All terrestrial life has the same genetic code, so this would be the best way to prove the idea of panspermia.  Of course, there would be huge implications for human psychology, even health, and our concepts of evolution, star formation, and even genetic engineering.  Now all we have to do is find extraterrestrial life!

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