Claims of a new form of life – one that has arsenic-based biology in place of the usual phosphorus – have been lauded, critiqued and ridiculed in a tumultuous fortnight of public science debate
For the last couple of weeks, headlines around the world have cried that another kind of life form has been found at the bottom of a poisonous lake in the US. As bloggers and scientists dig deeper into the story, however, the case for arsenic aliens grows thinner every day.
I’d like to focus a little on the actual chemistry in this article, but it’s worth briefly recapping the media frenzy around this story.
It all began with a mysterious press release from NASA, citing an “astrobiology finding that will impact the search for evidence of extraterrestrial life.” From there the speculation ran wild; journalists with keen news noses poked and burrowed, and all kinds of excitable headlines about aliens titillated the public ahead of the actual announcement.
Paul Sutherland, the “Sun Spaceman”, broke the story in the national press with a piece cleverly built on instinct and contacts. This splash story appeared before the press embargo was lifted, which in itself caused quite the storm. There’s more available on that aspect at the excellent Embargo Watch blog, if you’re interested in the complicated world of science journalism.
The research article itself, published in Science on 2 December, fuelled further stories of a less suggestive nature, with even the usual reliable sources still hedging their bets, but there were still doubters voicing concerns that the paper’s findings weren’t justified.
What’s the big deal? Not having a great knowledge of chemical biology myself, I had to do a bit of reading to even understand what the fuss was. The article claims that certain bacteria at the bottom of an arsenic-heavy lake had started to use the toxic element as a replacement for one of the fundamental elements of life: phosphorus.
Phosphorus, along with carbon, hydrogen, oxygen, nitrogen and sulfur, is one of the elements that all life is based on. The backbone of DNA is made of phosphorus compounds, and the membranes that hold cells together are made of phosphorus-based molecules called phospholipids. Adenosine triphosphate (ATP) is the phosphorus-based molecule that transfers energy in the human body. Bottom line: it’s essential for life as we know it.
The notion that another element might take its place is therefore quite a big deal. At the bottom of Mono Lake in California, which has no outlet to the sea and is extremely salty, bacteria appear to thrive in the extremely poisonous, arsenic-rich depths. The Science article claims the bacteria are not only able to survive, but actually take the arsenic and use it for growth and life.
On the face of it, from a purely chemical perspective, this isn’t necessarily a huge surprise. Arsenic sits just below phosphorus in the periodic table, and of course the reason they’re in the same group is that their chemistry is similar. This similarity actually contributes to arsenic’s toxicity – arsenates (AsO43-) are the same shape as the essential phosphate ion (PO43-), and break down the processes like energy transfer.
In water, as all life processes are based, arsenates form weaker bonds than phosphates. At least on a chemical level, the Science article makes no attempt to explain how these bacteria might stabilise these arsenates as part of their DNA. It’s this lack of justifiable chemistry, and questions about the experiments themselves, that have really sparked the scientific debate.
The analytical retribution has been swift and fierce. Never mind the extended hype of aliens and new life; scientists around the world have seriously questioned, and in some cases wholly denounced, the methods and findings of the article itself. That it got through the Science peer review process at all has risen more than a few eyebrows.
Rosie Redfield, a University of British Columbia academic, has vociferously refuted the claims of the article. She explains in great scientific detail the problems with the methodology and treatment of the results, but if it’s a bit hard to follow then skip to her excellent “Bottom line” summary near the end of the post. Her latest action has been to send a formal letter to the journal highlighting the article's flaws.
In short Redfield states that the researchers didn’t clean up their samples enough. Several routine DNA cleaning experiments weren’t carried out, and Redfield says consequently there was enough residual phosphorus to account for the bacterial growth.
The article authors’ response to criticism was equally contentious. In an email to news and research journal Nature the lead author, Felisa Wolfe-Simon, said "We are not going to engage in this sort of discussion … any discourse will have to be peer-reviewed in the same manner as our paper was, and go through a vetting process so that all discussion is properly moderated."
Given the extremely public launch of the article through the NASA press announcements, and the widespread and possibly inaccurate press coverage it garnered, it seems at best churlish to then entirely withdraw from the public arena to discuss the paper’s flaws.
The debate rages on, with the authors ardently defending their article and detractors demanding reviews of the science. I think this says a lot more about science communication than it does about science: scientific papers that will eventually be discredited are published every day, with little or no outrage from the science community at large.
What has really stirred up such feeling is the way that an article apparently riddled with methodological holes has generated such widespread reporting of allegedly inaccurate science. Ignoring the tabloid hype about alien life, the basic premise of the research is under heavy fire from critics who under normal circumstances might have had their say before the story came out rather than after.
If NASA hadn’t teased with such tempting-sounding (and some might say misleading) press announcements, the story would have been reported through the usual science channels. Perhaps then the reporting would have been more circumspect – as is often the case with science news.
As it stands, while scientists continue to wrangle over the truth, the public at large thinks there is no doubt that arsenic-based life exists in California. Some general news outlets are laudably following the fracas but in truth far more people have gotten their fill the Sun’s front page.
I’m not criticising the Sun, of course – a brilliant lead story for their paper after some proper journalism, and although there’s the expected hyperbole it doesn’t go too far beyond what the researchers actually claimed in the article.
I find myself coming back to one question: if a couple of chemists can read through the Science article once or twice and tear it to pieces, why is it happening only after it became an international news sensation? It seems we can lay the blame at many people’s feet, but none will accept it.
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