London, Jan 28 : Researchers have used strong microscope techniques to identify signs of cellular life in 2.7 billion-year-old Australian stromatolites - which are lumpy sedimentary rock formations.
Bacteria that secrete calcium carbonate, or lime, along with mucus, can build up layers of deposits to form these strange-shaped stromatolites that are observed today.
According to a report in Nature News, Kevin Lepot of CNRS (the French national centre for scientific research) and his colleagues used a powerful synchrotron light source to take a very close look at the ancient stromatolites from the Tumbiana Formation in Western Australia.
To do this, the team used a microscopy technique known as scanning transmission X-ray microscopy. In this way, Lepot and his colleagues saw globules of organic material shaped like cells inside the rock.
They also used the powerful Near-edge X-ray absorption fine structure (NEXAFS) spectroscopic technique to find out which molecules were present.
In the mix, they found carboxylic acids and other carbon-based molecules that are signatures of microbial life.
Mixed in with the organic globules were tiny crystals of the calcium carbonate mineral aragonite. Aragonite is a fairly unstable mineral, unlikely to be preserved unless protected by the remains of microbes.
"Seeing aragonite is another strong indication that microbes were present," said Lepot.
According to the report, this is by far the oldest aragonite found; the previous oldest sample has the youthful age of 350 million years.
The discovery of these unambiguous remains of cells in these rock formations is expected to help scientists hunting for early signs of life on Earth.