Cast your mind back six months, to late November 2010. Wikileaks had unveiled the first goodies from its cache of 250,000 State Department cable. Hosni Mubarak’s National Democratic Party was coasting toward yet another easy win in Egyptian elections. And, for just a few days, a lot of us wondered if NASA had discovered aliens.

If you’ve forgotten about that otherworldly dalliance, today is a good time to refresh your memory. On Nov. 29, NASA announced that it would soon hold a press conference to “discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life.” Wild speculation ran amok—perhaps scientists had found living things on one of Saturn’s moons. At the press conference, the scientists did not unveil an actual extraterrestrial, but they did have big news. A new paper had just been published in the journal Science, they said, which described bacteria that seemed able to build their own DNA from arsenic. If that were true, it would be an historic discovery, because no such ability has ever been found among Earth’s life-forms.

Technically speaking, though, Science didn’t so much publish the paper last fall as post a web-only version on a page called Science Express. Month after month went by, and it didn’t appear in the actual paper-and-ink journal. Rumors circulated that a number of scientists had sent in formal criticisms (known in the business as “technical comments”), arguing that the study hadn’t come close to demonstrating that the bacteria were growing on arsenic. But these never appeared in print or online. Finally, this morning, Science posted eight critiques of the paper to the website, along with an extended response from the original authors. The June 3 print edition of the journal will include both the paper itself and the follow-up discussion. For scientists who only get their information in print, this may be the first they’ve heard anything about a longstanding controversy that’s come to be known over the past six months by its Twitter hashtag: #arseniclife.

For those of us who have been tracking #arseniclife since last Thanksgiving, however, today comes as an anticlimax. There’s not much in the letters to Science that we haven’t read before. In the past, scientists might have kept their thoughts to themselves, waiting for journals to decide when and how they could debate the merits of a study. But this time, they started talking right away, airing their criticisms on the Internet. In fact, the true significance of the aliens-that-weren’t will be how it helped change the way scientists do science.

NASA, Science, and the arsenic-researching scientists kicked off the whole affair by doing what scientists and scientific institutions always do. They were excited that they had made a game-changing discovery, so they submitted a paper to one of the world’s top scientific journals. The paper went through peer review, and then reporters were given copies of the paper in exchange for agreeing to an embargo. NASA scheduled their attention-grabbing press conference to begin at 2 p.m. on Dec. 2, the very minute that Science lifted its embargo.

Everything seemed to be going according to plan—until NASA posted a terse, mind-bending announcement of a press conference about extraterrestrials. I suppose NASA imagined that the announcement would be noticed only by science writers who knew the drill, and understood what the press conference would be about. If that’s true, they exhibited some woefully 20th-century thinking. Bloggers quickly picked up on the announcement, and the possibility that we’d discovered E.T zipped through the media ecosystem, eventually ending up on the websites of major news organizations.

The longer that people speculated, the more absurd the embargo policy became. Science and NASA could have put a stop to all the misinformation and hype with the simple click of a “publish” button. Instead, Science and NASA continued with their ritualized silence. Only at the press conference did they set matters straight: No, they hadn’t found life on one of Saturn’s moons. Instead, they had found what seemed to be a remarkable microbe in Mono Lake, California. If microbes could live on arsenic here on Earth, they argued, then we should expand the range of planets on which we search for life.

The paper received massive press coverage around the world. The first wave of articles only offered a faint hint that some scientists were suspicious. It turned out there was actually a deep vein of skepticism. Many scientists believed that the #arseniclife team were leaping to conclusions. Their experiments weren’t rigorous enough to rule out more prosaic explanations for the data—for example, that the bacteria were actually tucking away arsenic in pouches, rather than using it to build their DNA.

In earlier times, such critics didn’t have many options. They could write to Science and hope that their letter would be published long after the public’s attention had turned to other things. They could write to their local newspaper and try to sum up their objections in 50 words. They could grouse over a beer with likeminded colleagues. Now, however, they can form an online community. Blogging scientists read the #arseniclife paper and aired their complaints. On Twitter, they kept each other up to date on new developments in the story. Within a couple weeks the New York Times and the Washington Post were reporting not on the Science paper, but on the online debate. The center of gravity had shifted.

The discussion spread into the websites of other scientific journals, even though Science had still not yet formally published the original paper in print. At ACS Chemical Biology, Mostafa Fekry of the University of Missouri and his colleagues explained how the bonds in an arsenic-based DNA molecule would fall apart in a fraction of a second. * Simon Silver and Le Phung of the University of Illinois published a scathing critique in the journal FEMS Microbiology Letters, calling the results “science fiction.”

There was no bright line dividing what these scientists wrote in scientific journals and what turned up in other forms of online communication. Earlier this week, Silver went to the annual meeting of the American Society of Microbiology in New Orleans to explain why he thought the arsenic paper was so flawed. Several scientists in the audience shared his talk with their followers in a series of tweets, such as “Silver - the 1 experiment to run would of been - acid hydrolysis of the DNA and radio labelled arsenic - if it was in the DNA it would show!” The tweets could use some copy-editing and context, but they were effective for spreading the word.

There were two groups of people glaringly absent from this online discussion. One group included the supporters of the arsenic researchers. I have found only one third-party defense of the work online, in a review in the journal Bioessays. The other group comprises the authors of the paper themselves. When I asked them to comment for my previous Slate article on the controversy, they said they would only do so in a peer-reviewed journal. Yet they did not actually take a vow of silence. Co-author Ronald Oremland participated in another press conference at the American Geophysical Union in December, where he declared, “I don’t want to get involved in what can end up in a Jerry Springer situation, with people throwing chairs.”

Both NASA and the authors tried to play the bloggers-in-their-pajamas card, but it was a losing hand. For one thing, the people who were talking on blogs and Twitter were not in their pajamas. Many of them were in lab coats. They were practicing scientists who wanted to have an open debate. For another, the arsenic scientists didn’t exactly flee the media spotlight. The lead author, Felisa Wolfe-Simon, delivered a high-profile TED lecture in March. Three months later, she appeared in a full-page profile in the June issue of Glamour entitled, “This Rising Star’s Four Rules For You.”

The formal response today in Science marks the first time that Wolfe-Simon and her colleagues have directly responded to their critics, rather than having a one-way conversation. But this exchange was immediately folded into the bloggy discussion online. Rosie Redfield, a University of British Columbia microbiologist who raised the first red flag about the arsenic paper last fall and who wrote one of the comments published today in Science, immediately had this to say on her blog:

“The authors don’t report any new experiments. Most of their responses take the form of ‘our interpretation could be correct on this point if…’. In many cases there is indeed a small possibility that it could, but there are so many of these points of interpretation, each with only a very small probability of being correct, that I don’t think anyone will find the arguments convincing.”



Redfield and her colleagues are starting to carry out a new way of doing science, known as post-publication peer review. Rather than leaving the evaluation of new studies to a few anonymous scientists, researchers now debate the merit of papers after they have been published. The collective decision they come to stays open to revision.



Post-publication peer review—and open science in general—is attracting a growing number of followers in the scientific community. But some critics have argued that it’s been more successful in theory than in practice. The #arseniclife affair is one of the first cases in which the scientific community openly vetted a high-profile paper, and influenced how the public at large thought about it.

In her blog post this morning, Redfield wrote that Wolf-Simon and her colleagues supplied some more details about their experiment in their formal response that weren’t in the original paper. She planned to address those details in a post later in the day. The conversation, in other words, goes on.

Correction, May 31, 2011: This article originally misidentified the publication ACS Chemical Biology as ASC Chemical Biology. (Return to the corrected sentence.)