Archives For abiogenesis

alien bacteria

One of the topics that’s been prominently featured on Weird Things has been panspermia, the hypothesis that life can originate somewhere in the galaxy and spread though asteroid or comet impacts, or even forward contamination by alien spacecraft. We know that amino acids can form all on their own when certain molecules are irradiated, that some creatures can easily survive a trip though space, and there’s evidence that molecules crucial for life here may have a strong link with primordial impacts. Now, true, the theory has been abused by those who either do not understand what it actually entails, or by those who just refuse to keep up with the science and spend most of their time accusing some secret anti-panspermia cabal trying to keep them down, but overall, it’s quite sound which is why it’s still being kept in mind by astrobiologists. Or so you would think unless you go by a Scientific American blog post which says the following…

In some ways the motivation for proposing this kind of cosmic panspermia is a little dated. It comes from a time when we felt that the origin of life of on Earth was such a mystery, and such an unlikely event, that it was convenient to outsource it. Although this didn’t actually solve the real question of life’s origins, it meant that a specific origin ‘event’ could be extremely rare among the 200 billion stars of the Milky Way yet life would still show up in other places.

These days I think our discoveries about the remarkable abundance and diversity of so-called pre-biotic chemistry [...] in every nook and cranny of our solar system, and even in the proto-stellar nebula of other stars and the wilds of interstellar space – swings the pendulum back to Earth. Nature seems adept at making all the pieces for life, apparently raising the odds of local bio-genesis.

How are these two thoughts connected again? I’m not exactly sure how life being very adaptable would mean that it raises the odds of Earth being its origin because we’re talking about evolution rather than abiogenesis. Caleb Scharf, the scientist who wrote the post, seems to be making the same kind of mistake many creationists do when trying to ridicule evolutionary theory by asking how life would’ve come from non-life and nothing that evolution fails to answer this question. So it’s little wonder that whatever life gets here or starts here would fill every available nook, cranny, and environmental niche since natural selection would favor their reproduction. But whether the origin of these species is on Earth or in space is more or less a toss-up if we’re considering just how well they adapted to their current environments.

Yes, we could say that it’s more likely that life originated on Earth because space is vast and the odds of enough comets and asteroids hitting the planet at just the right conditions for life to take hold are astronomical, literally, so it makes sense to look for an explanation that makes life more likely to arise here. That explanation may not be right, but we don’t have a complete picture of how it came to be and so we’re still trying to find viable ideas that seem to fit the evidence we’ve observed so far. But an important part of the process is not to discard hypotheses without any evidence that they simply don’t fit with the observations, something that Scharf does with an odd certainty about the habitability of promising places in the solar system by hearty microorganisms that should dominate the universe based on the way natural selection works.

But the problem, and the potential paradox, is that if evolved galactic panspermia is real it’ll be capable of living just about everywhere. There should be [organisms] on the Moon, Mars, Europa, Ganymede, Titan, Enceladus, minor planets and cometary nuclei. Every icy nook and cranny in our solar system should be a veritable paradise for these ultra-tough life forms, honed by natural selection to make the most of [the] appalling conditions. So if galactic panspermia exists why haven’t we noticed it yet?

He then goes on to answer his own question by saying that we probably haven’t looked all that hard in all these places, don’t know for what we’re really looking, or possibly both, and ponders would it would mean if we kept searching and found nothing. You can tell that he’s really pushing for the Earth-centric explanation and again, as elaborated above, I can see why, but his primary reason for pushing it seems to be based on a very strange confusion between abiogenesis and natural selection with no facts to back it up. The argument seems to be: we know more extreme organisms on Earth, natural selection seems to be doing it’s job, we haven’t explored all of the promising candidates for life in our solar system in sufficient detail and we don’t really know what we’re trying to find and how we’ll know we found it, therefore, life arose on Earth. Doesn’t seem like a scientific train of thought to me, especially with all the evidence that there was at least an important role being played by organic matter or microorganisms from space…

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Former science writer John Horgan isn’t happy with the media coverage of Venter’s newest experiment with synthetic genomes and dead cells, and while downplaying what he sees as needless, unwarranted media hype, managed to take out his displeasure not only on pundits and philosophers trying to make a story where one doesn’t exist, but the scientist himself with a rather unflattering description of the biologist and his efforts in his guest post at SciAm. In fact, that dig at Venter’s ability to get press coverage is his opening hook…

Venter is the Lady Gaga of science. Like her, he is a drama queen, an over-the-top performance artist with a genius for self-promotion. Hype is what Craig Venter does, and he does it extremely well, whether touting the decoding of his own genome several years ago or his construction of a hybrid bacterium this year. In a typical Venter touch sections of the bacterium’s DNA translate into portentous quotes, such as this one from James Joyce: “To live, to err, to fall, to triumph, and to re- create life out of life.”

Now, is it just me or does Horgan have some sort of a bone to pick there? Sure, Venter is well connected and well funded, his projects are extremely ambitious, and he likes to set bold goals. However, he doesn’t pitch a pet project as a potential solution to all universal problems like Wolfram, or just talk a big game, aiming for the sky while still learning how to walk, like de Gray. He lays out his goals quite clearly, focuses on the actual science at hand, and produces tangible results. His presentation at TED in 2008 touched on the potential of creating synthetic life to solve global problems, but he didn’t imply that the technology was almost there and if we want to see it come to fruition, we should just watch him and his team. Ok, so he put in a watermark with a high brow quote into a synthetic genome, so what? What would Horgan rather have him do? Add “this is a test genome” and nothing fancier than that, otherwise Venter is an unabashed glory hound?

It seems that Horgan is taking out his frustration at the sensationalistic media coverage of scientific topics, an unfortunate norm nowadays, at a scientist who gave them a great story from which to spin tales of the future and fantastic proclamations. While he emphasizes that Venter didn’t actually create new life in the lab, neither did Venter and the only people who did were reporters and philosophers, who tend to either lack the scientific skills to adequately interpret what actually happened, or want to make a big pronouncement despite lacking a reason to do so. And to counter them, Horgan decided to bend the story to the other extreme and plays up the mysteries of life’s origins and how far we seem to be from understanding how living things appeared.

[Bioethicist] Arthur Caplan declares that Venter and other scientists have dispelled the notion that life “is sacred, special, ineffable and beyond human understanding.” Wrong. We still have no idea how life began, or whether life exists only here on our lonely planet or pervades the cosmos. One of the great ironies of modern science is that as we gain more power over life, it remains just as fundamentally mysterious as ever.

Sorry Mr. Horgan but no. Scientists and many of those who follow their work understand life as a very complex biochemical reaction, a view which already demotes life from its post as a sacred, incomprehensible enigma so we can study it in the lab. Whatever you say about Venter’s experiments, they do help us get a much better idea of how life began by experimentally reducing living things down to their most basic parts, drawing a more defined line between living and non-living. When we know what chemistry has to take place in order to make a living, self-reproducing cell, we can further break it down in its core components and figure out some possible scenarios of how the building blocks of our universal common ancestral population came together, as well as from where these building blocks might have come.

We will probably never know exactly how life got started on Earth, but we’re seeing some glimpses as to how that may have happened thanks to experiments done by Venter and his team, as well as those what build on his work. There are many years of work still ahead, but to pretend that we’re just as ignorant about the origins of living things as we were some 50 years ago, when DNA was just being formally identified for what it really was and the concept of synthesizing genes was still the stuff of wild, science fiction comic books, is simply no longer an option. At least not an intellectually honest one anyway.

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What do you get when you take pyrimidine molecules, freeze them in a vacuum to -340°F, then expose them to ultraviolet radiation you’d find in space? Think about it for a second. If you took a few extra credits in a college biology class, you may remember that your DNA contains purines and their chemical relatives pyrimidines, so the end result of changing a pyrimidine should have something to do with heredity. And indeed it does. If your experiment accurately replicates what the NASA Ames Research Center has been able to do, you’ll get one of the key components of genetics; uracil. Yes, the same uracil which replaces thymine in an RNA strand and pairs up with adenine during the production of proteins. Proteins composed of amino acids. That also have a cosmic origin and acquire a bias in chirality (the direction in which a molecule is wound) in meteorites.

bombardment

So not only is space full of comets and asteroids rich with water ice, amino acids and simple sugars that can bind into more complex precursors of DNA and RNA strands, but it seems that conditions in interstellar space could also alter carbon rich molecules into full blown nucleobases. Here’s how the process works…

The researchers thought that if molecules of pyrimidine could survive long enough to migrate into interstellar dust clouds, they might be able to shield themselves from radiation destruction. Once in the clouds, most molecules freeze onto dust grains. [...]

They found that when pyrimidine is frozen in water ice, it is much less vulnerable to destruction by radiation. Instead of being destroyed, many of the molecules took on new forms, such as the RNA component uracil, which is found in the genetic make-up of all living organisms on Earth.

For those of us wondering how life could arise on a newly formed, barren planet that just started cooling from millions of years of collisions, experiments like this are constantly pointing skyward and showing us that life’s chemistry kit was quite literally raining down on Earth billions of years ago. Maybe biology and astronomy are eventually destined to join at the hip when it comes to studying abiogenesis and it’s just a matter of time until colleges start offering astrobiology programs for those with a passion for space and studying the biosphere.

See: Nuevo, M., Milam, S., Sandford, S., Elsila, J., & Dworkin, J. (2009). Formation of Uracil from the Ultraviolet Photo-Irradiation of Pyrimidine in Pure H2O Ices Astrobiology, 9 (7), 683-695 DOI: 10.1089/ast.2008.0324

[ illustration by CG artist and designer Mario Iliev ]

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