Canadian researchers say they have discovered what appear to be trails left by microbes living inside volcanic rock, which they believe are new evidence of life on Earth over three billion years.

The trails, found in 3.35-billion-year-old rocks in Western Australia, constitute the strongest evidence to date of ancient life and could tell geologists where to look for signs of life on other planets, said the authors of a study published in the June issue of Geology, the journal of the Geological Society of America.

"Volcanoes aren't something you normally think of as being a spawning ground for life, but we've found this evidence from this very early period of Earth's history," said University of Western Ontario geologist Neil Banerjee and the study's lead author.

The team of researchers, led by University of Western Ontario geologist Neil Banerjee and including three scientists from the University of Alberta, had previously uncovered similar fossil trails in South Africa and dated those at 3.5 billion years in a 2004 article in Science.

Those findings were criticized for dating the surrounding rock to determine the fossil's age and not the actual track left behind by the organism. But this time the researchers were able to date the track itself with the help of a laser-plasma mass spectrometer at the University of Alberta, said Banerjee.

The researchers found traces of carbon and nitrogen, elements found in organic matter, as well as mineral nutrients such as iron and manganese. Adding weight to their findings were similarities between their samples and microscopic tracks from more recent volcanic rock where DNA was recovered.

Banerjee's group is not the first group of researchers to have claimed to find evidence of ancient life in Australia. A team of scientists published a paper in the journal Nature last June suggesting oddly shaped dirt mounds in Western Australia called stromatolites are a result of a buildup of sand around ancient microbes also dating from more than three billion years ago.

Scientists have long speculated that life on Earth might have formed in the Archean age — about 3.5 billion years ago — but finding hard evidence of its existence has been hard to come by and harder to prove, in part because it would be virtually impossible to recover the DNA that forms the building block of life from so long ago.

The oldest widely accepted DNA sample comes from 400,000-year-old plants found in ice in Siberia.

Banerjee said his group's next project, funded by the Canadian Space Agency, will take them to study volcanic rock near Lake Abitibi near the Ontario-Quebec border, in the hopes of learning more about the conditions that might support life on other worlds.

"These volcanic rock formations are very common on Mars, so as our research continues it could help shape future space missions and where we search for life," he said.