Chemicals found in tiny rocks from Australia likely remains of some of Earth’s first life forms, study finds

Chemicals found in 3.4 billion-year-old rocks have confirmed them as contenders for the title of oldest evidence of life on Earth.

Discovered in Western Australia back in 2013, the Strelley Pool “microfossils” are thought to be all that remains of ancient bacteria.

But the passage of time takes its toll on all fossils, especially microscopic ones.

This means any remains that are discovered are the subject of enormous debate in the scientific community.

In their latest study, a team of scientists used the chemical traces left on the miniscule structures found at Strelley and compared them with the chemical signatures of modern-day bacteria.

They also used more recent microfossil evidence from 1.9 billion year-old Canadian rock formations as an additional comparison, and found that the characteristics of each were roughly the same.

“We demonstrate that the elemental and molecular characteristics of these 3.4 billion year-old microfossils are consistent with biological remains, slightly degraded by fossilisation processes,” said Dr Julien Alleon, a Massachusetts Institute of Technology scientist who led the study.

“This effectively supports the biological origin of the Strelley Pool microfossils.”

Dr Alleon said it was remarkable that these “echoes of past life” have survived for so long, especially given the extreme conditions they would have been exposed to over the years.

“We know from the molecular structure of the microfossils that they have been exposed to temperatures of up to 300C for long periods. And yet we are still able to see signs of their original chemistry,” he said.

Their results were published in the journal Geochemical Perspectives Letters.

The tiny structures the researchers examined belong to a limited club of formations touted by different groups as the oldest ever fossils.

Even in the wider Strelley Pool formation, which geologists think was once submerged underneath a shallow ocean, there are other ancient structures called stromatolites thought to be the remains of ancient colonies.

Some proposed microfossils discovered in Canada have pushed the origin of life on Earth back even further to over 4 billion years ago.

Besides confirming that life’s history stretches back at least 3.4 billion years, the scientists behind the new study – which was presented at the Goldschmidt geochemistry conference in Boston – want to use their methods to investigate specimens with competing claims.

“There are competing claims over which microfossils are actually the world's oldest, this analytical strategy needs to be applied to other ancient samples to help settle the controversy,” said Dr Alleon.

Professor Vickie Bennett, a researcher at the Australian National University with expertise in this area who was not involved in the new study, agreed this work provided “compelling evidence” that the Strelley microfossils were evidence of life on ancient Earth.

However, she said the same techniques would not be able to end the debate once and for all.

“The techniques used here are not applicable to the older rocks that host the claims for the oldest terrestrial life, as these rocks were exposed to much higher temperatures,” she explained.

“These samples include the 3.7 billion year old stromatolites from Isua, Greenland and the 4.1 billion year old Canadian microfossils.

“However, this work shows how quickly the field is developing and that new capabilities for testing and confirming earlier evidence of life are in reach.”