Mar 25, 2011 08:10 GMT  ·  By
Artist's rendition of the environment in which the cyanobacteria found in Australia are thought to have formed in
   Artist's rendition of the environment in which the cyanobacteria found in Australia are thought to have formed in

According to the results of a new investigation, the formations long-thought by experts to be fossils of the oldest known microbes to have lived on Earth may in fact be microscopic mineral deposits.

Scientists behind the research say that these findings should help inform astrobiologists in avoiding labeling all peculiar formations they encounter in space rocks as lifeforms. That is not to say that life may not exist within. The team is simply urging more caution.

The take-away message from all of this is how can you be certain that a certain formation in a meteorite is life, when we don't even know what life looks like here, on our own planet.

At this point, the oldest known microbial fossils are a number of microscopic structures that experts identified in western Australia's Apex Chert formation some two decades ago. The study site was determined to be 3.5 billion years old, Space reports.

All of the structures that experts said were fossils of microorganisms were uncovered within a sample slice less than 300 microns thick. This is about three times as wide as the diameter of a human hair.

The research teams that carried out the investigations at the time said that they had discovered blue-green algae (now called cyanobacteria) fossils, that were trapped in a rock matrix rich in silica. The entire geological structure had formed all those eons ago in a shallow water environment.

Twenty years after those conclusions were published, the international scientific community is still in doubts over the authenticity of the evidence, and numerous, heated debates are still raging on.

One of the things that indicates the fossils may have been lifeforms is their carbon-based chemistry. Conversely, the discovery of branching structures leading away from them convinced others that they are dealing with a mineral formation rather than a cyanobacteria.

According to the new research, the formations may not be carbon-based after all. A team led by Craig Marshall, a geospectroscopist at the University of Kansas, proposes that they are just a series of fractures in the surrounding, silica-rich rock, that have been filled with crystals over time.

“It's one of those funny moments in science when you go out to do one thing and it completely flips 180 on you. We were interested in developing new methods of looking at ancient microfossils, and so we were drawn to the Apex Chert as these putative microfossils are so iconic,” Marshall says.

“However, when we started working on the rocks, we discovered things were a little more complex than we thought they would be,” he goes on to say.

Further studies will undoubtedly follow this discovery. The work, published in the February 20 online issue of the esteemed journal Nature Geoscience, is bound to entice even more controversies among experts.

“If it is really this hard to find convincing evidence for life on early Earth when we know there is life on Earth now, then it becomes clear that we need to be extra cautious interpreting data collected on Mars,” adds Alison Olcott Marshall.

The expert, who holds an appointment as a paleobiogeochemist at the University of Kansas, is a co-author of the new Nature paper.