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| Are these tubules evidence of alien life? (Image: Richard B. Hoover/Journal of Cosmology) |
First seen on 14 May 1864, in the shape of an enormous fireball in the sky over southern France, the Orgueil meteorite is making headlines again – though this time its appearance has mostly been ill-received.
Last week, NASA scientist Richard Hoover at the Marshall Space Flight Center near Huntsville, Alabama, published a paper in the Journal of Cosmology claiming that fragments collected from the Orgueil meteorite and two similar meteorites contain fossilised bacteria.
Hoover made nearly identical claims in 2004 and again in 2007. This time, Hoover says that fibrous structures in the meteorites are almost exactly the same size and shape as photosynthetic bacteria found on Earth, especially one relatively large bacterium called Titanospirillum velox.
Macaroni, anyone?
Hoover fractured pieces of the Orgueil meteorite, two other CI1 carbonaceous chondrites – a rare class of meteorite of which there are only nine known specimens – and used an imaging technique called field emission scanning electron microscopy to closely study the interiors of the fragments.
In his paper, he juxtaposes pictures of tubular and ribbon-like squiggles on the inner surface of the space rocks and pictures of bacteria found on Earth. They all look like black-and-white photos of dried macaroni.
In addition to this shape-based evidence, Hoover provides chemical evidence, arguing that the squiggles contain more carbon than the meteorite matrix in which they are suspended, suggesting they were once alive.
Scientists are currently debating whether there is enough evidence to accept that the filamentous structures inside the meteorites are, as Hoover claims, biological organisms from outer space, whether they are in fact terrestrial bacteria that wormed their way into the meteorite after it crashed or whether the squiggles are nothing more than naturally occurring mineral structures that, to an eager researcher's eye, may very well look like bacteria. So far, the consensus is that the last of these possibilities adheres most closely to principle of Occam's razor.
See what you want
Microbiologist Rosie Redfield at the University of British Columbia, Vancouver, critiqued Hoover's study on her blog, RRResearch. She remains unconvinced by the evidence for alien life presented in the study. Although Redfield chastises Hoover for not properly detailing how the samples were stored over the years – and therefore how they could have been contaminated by earthly bugs – she is more concerned that Hoover apparently did little to rule out the possibility that the shapes he saw are simply not life forms, extraterrestrial or otherwise.
"The first thing you learn when you do electron microscopy is that it's really easy to see anything you are looking for – if you have a good search image in your brain, you can find it," she says. "I think those squiggles are just places in the rock where the minerals happened to arrange themselves in a squiggle shape. Minerals readily grow into fibres."
The often confounding prevalence of minerals that look an awful lot like living things is exactly what geologist Alison Olcott Marshall at the University of Kansas in Lawrence confronted in a Nature paper published last month.
Look closer
Olcott Marshall and her colleagues revealed that what we thought were the oldest known bacterial fossils on Earth are only deceptive patterns formed in the rock by geological processes. The researchers sliced the 3.5-billion-year old Apex Chert rock containing the alleged fossils into 30-micrometre sections, thinner than any previously studied slices, and shone a powerful laser at them to get a good look under the microscope.
The new analysis confirmed that the fibrous structures researchers had originally identified as fossilised cyanobacteria were in fact fractures in the rock filled with inorganic haematite and quartz.
"One lesson we learn over and over again is that morphology is very common between minerals and life," says Olcott Marshall, who is also unconvinced by Hoover's new paper. "Finding circles and wiggles is not necessarily evidence of life."
Not feeling the chemistry
Olcott Marshall is not only highly sceptical of the morphological evidence, she is disappointed by Hoover's chemical evidence. "I really wish there was more evidence separating the composition of these structures from the carbonaceous chondrite around them," she says.
"It looks like some squiggles have more sulphur and less silica than the background rocks, but to my eye the data show that nitrogen, oxygen, carbon and phosphorous are all evenly dispersed." If the tubules were in fact life forms, these organic compounds should be present in higher quantities wherever a squiggle graces the rock, she says.
Redfield says that Hoover explains away the lack of nitrogen in the squiggles by claiming that they are fossils and that even fossils on Earth do not contain much nitrogen. But if the Orgueil meteorite does in fact conceal fossilised bacteria, there is still the question of where these bacteria came from in the first place and how they apparently managed to live inside a meteorite hurtling through space.
Not so bright
Hoover compares the structures inside the meteorite to cyanobacteria, which require light and water to produce food through photosynthesis. Although the meteorite does contain water and may have originated on an icy comet, its interior is not exactly the brightest environment around. If the squiggles are bacteria from Earth, it is unclear how they would have fossilised between 1864 and now.
This is not the first time that scientists have grappled with the immense difficulty of interpreting lifelike structures they sometimes find within meteorites. In 1996 David McKay of NASA's Johnson Space Center in Houston, Texas, published a paper in Science claiming that a meteorite called Allan Hills 84001 contained fossilised Martian microbes. The announcement caused such a hullaballoo in the scientific community, media and public alike that President Bill Clinton promptly delivered a televised public address.
Scepticism about those findings mushroomed: some researchers argued that the nanometre-scale filaments were too small to be living things – even bacteria – while others thought contamination by terrestrial microbes was a simpler explanation than Martian life. Today, 15 years later, scientists are still debating whether Allan Hills 84001 harbours tiny hitchhikers from the Red Planet.
Worlds at our feet
Scientists seize the opportunity to examine meteorites for signs of alien life because rocks that fall from space bring pieces of other worlds to our feet – which is quite a bit easier than travelling all the way to Mars or trying to scoop a passing comet into a space station.
But even with tools that let them examine meteorites in exquisite detail, researchers cannot easily distinguish a squiggle in a rock from the remains of a living creature, which begs the question: what is the gold standard for evidence of alien life? Assuming that a little green man is not going to drop by NASA's headquarters any time soon, what will convince scientists that they have found extraterrestrial life?
The answer, it seems, is nothing short of "extraordinary evidence" – a phrase that is currently leaping from the lips of scientists around the world as they argue over Hoover's new study.
Gold standard
"As for the gold standard, supposed fossils would be low on the list," said Jeffrey Bada, a geochemist at the Scripps Institution of Oceanography in La Jolla, California. "There are just too many non-biological artefacts. The not-so-short answer is that several different lines of evidence are going to be required."
Olcott Marshall agrees. "Morphology alone isn't enough; geological context isn't enough – you need all the pieces. You need multiple lines of evidence: morphology that is highly reminiscent of biology, a geological context that makes sense and strong chemical evidence."
In the specific case of Hoover's new study, none of these threads of evidence is particularly taut. "This newest paper is very similar to his older papers and to the best of my knowledge there is no support in the meteorite analysis community for the rather extraordinary claim that what he is seeing is alien life," says Carl Pilcher, director of the NASA Astrobiology Institute in Mountain View, California.
Media storm
More than a few scientists and journalists have argued that the evidence Hoover does offer is all the more ensconced in suspicion – though certainly not invalidated – by the journal in which he chose to publish: the peer-reviewed, open access Journal of Cosmology, which announced it is likely to go out of business in a few month's time.
The journal's editor-in-chief, Harvard University's Rudy Schild, is a proponent of panspermia – the idea that life abounds in the universe and that a meteorite crawling with alien organisms likely seeded life on Earth.
The journal has startled and confused the media with a series of atypical press releases that, for example, defend Hoover's choice to publish with the Journal of Cosmology instead of Science or Nature because "Editors at Science have been accused of using the Bible to make editorial decisions". It also alleges anti-competitive practices have been aimed at the Journal of Cosmology, and accuses other media outlets of plagiarism.
Back and forth
In an official press release, NASA distanced itself from Hoover's findings: "NASA cannot stand behind or support a scientific claim unless it has been peer-reviewed or thoroughly examined by other qualified experts. This paper was submitted in 2007 to the International Journal of Astrobiology. However, the peer review process was not completed for that submission. NASA also was unaware of the recent submission of the paper to the Journal of Cosmology or of the paper's subsequent publication."
However, the Journal of Cosmology's editorial guidelines state that all articles are peer reviewed. In an email to New Scientist, the journal's managing director Lana Tao explained that Hoover's article was first submitted in November 2010, reviewed by Chandra Wickramasinghe, who requested certain changes and sent out for external review by five experts.
Hoover then revised the paper and it was subsequently reviewed by two external referees, who requested minor revisions. None of the external reviewers have been named.
Hoots and jeers
In a move unusual for research journals, the Journal of Cosmology sent 100 requests for additional review and analysis from scientists and has published 21 responses so far, most of which largely applaud Hoover's study, raising minor quibbles here and there.
It could all yet prove to be a tempest in a teacup, though. It appears likely that Hoover's study may soon be ignored by the majority of the scientific community, instead of enjoying a healthy debate such as that raised by McKay's 1996 paper on the Mars meteorite. Redfield says that a microbiologist that she knows refused to read it.
The Journal of Cosmology, however, does not show signs of backing down. "It should be expected that a discovery as momentous as reported by Dr. Richard Hoover, would be met with hoots and jeers," said Lana Tao in another email. "The choice is simple: Scientific discourse vs psychosis. Hysteria and lies do not constitute scientific doubt. They are calls for medication."
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