Life on Mars? No it wasn't, according to a team of American scientists, who have produced a comprehensive rebuff to the claims by the US space agency Nasa that it had found fossil evidence of past extra-terrestrial life in a meteorite from Mars.
In fact, according to Ralph Harvey, leader of a team at Case Western Reserve University in Cleveland, Ohio, the things that Nasa mistook for fossil bacteria in the potato-sized meteorite ALH84001 were fractures in the rock, allied to a byproduct of the technique used to photograph those fractures.
"Sometimes even nature has a perverse sense of humour," he said, adding that the worm-like threads that Nasa's multidisciplinary team described as nano-fossils were formed by geological, not biological processes.
After six months of studying the meteorite, which was found in Antarctica in 1984 having split off from Mars about 4 billion years ago, Dr Harvey concluded: "We have now found two different types of mineral forms in ALH84001 that look just like nanofossils, but they are strictly non-biological." His team's findings are reported today in the science journal Nature.
The latest paper joins a growing list of those which have come down against the excited announcement in August 1996 by Nasa that ALH84001 showed signs of having once harboured life.
At the time, Nasa's scientists said that any confirmation of their claims would have to come from the rest of the world science community. However, that approval has been slow to arrive. In fact, no major piece of research has backed Nasa's claim, while many studies have chipped away at pieces of the series of hypotheses which are necessary to support the claim.
A separate reason why Nasa's claims were greeted with surprise by some scientists is that ALH84001 had been extensively studied by other scientists - including some in Britain - before passing to Nasa. Those researchers had found nothing extraordinary.
But the Nasa team examined sections of the meteorite using an electron microscope. There, they said they discovered worm-like features. They said that peculiarities of the surface features meant that they could only have been made by some sort of bacterial life, which then became fossilised. The rock in which the bacteria had lived was then sheared off Mars and eventually fell to Earth.
The CMRU team disagrees strongly. "Peculiar surface structures or segmentation on the worm-like forms are artefacts from conductive metal coatings, applied to the samples for imaging in the electron microscope."
Nasa's response will probably be that the best way to be certain will be to send missions to the Red Planet to prospect directly for life. In which case ALH84001 will have succeeded in putting life into Nasa, if not its planet of origin.Reuse content