Martian rock 'does contain life'

Is this a fossilised micro-organism from Mars? ©Nasa

By Dr David Whitehouse BBC News Online science editor

The strange shapes seen in a rock from Mars that some researchers say are fossilised bacteria really are tiny micro-organisms, say US researchers.

But while they are confident the Mars rock contains ancient life they cannot quite bring themselves to say it comes from the Red Planet; it might be Earthly contamination.

Despite the uncertainty about their origin, establishing that the small structures really were living things, and not just mineral globules, would be an advance in a field that has sharply divided opinions.

Lawrence Taylor, of the University of Tennessee, told BBC News Online that so-called "nannobacteria" found on Earth resemble those found in the Mars rock." The next task is to find a way to determine if they really came from Mars.

Life on Mars?

Since the dramatic announcement in 1996 by US space agency (Nasa) scientists that there were several lines of evidence that suggested rock ALH84001, picked up from Antarctic ice but originally from Mars, contained evidence of life, scientific opinion has been divided between those who wanted to be persuaded, and those who did not.

Nannobacteria seen in the Mars rock. © Robert Folk.

Since then the rock has been extensively analysed and many papers written, but few people have shifted their original viewpoints.

One camp has looked at magnetic grains in the microfossils saying that they appear identical to magnetic grains found in some terrestrial bacteria. Another group of researchers studied how carbon deposits in the rock were formed, looking to see if they were deposited at low enough temperatures so they could be by-products of life.

Whether these bodies originated on Mars, or are Antarctic contamination remains a valid question

Lawrence Taylor
University of Tennessee

Rival researchers have argued that the very small size of the purported micro-organisms make it unlikely that they were living things because they are too small.

In the past few years, however, some researchers, principally Robert Folk of the University of Texas, have put forward evidence that terrestrial nannobacteria do exist and add significantly to the Earth's biomass.

The latest study, by Folk and Lawrence Taylor, casts doubt on the lower size limit for life viewpoint. Some of the larger bacteria found in ALH2004 are actually close in size to the smallest terrestrial organisms.

But if the case for the fossilised micro-organisms in ALH84001 is strengthened somewhat, the big question remains: where did they come from?

"We conclude that the nanobodies that are so abundant in ALH84001 are indeed nannobacteria. However, whether these bodies originated on Mars or are Antarctic contamination remains a valid question," say the researchers.