Ancient cone-like fossils suggest life on Earth may go backmore than 3.7 billion years
‘If these really are the figurative tombstones of ourearliest ancestors, the implications are staggering’
Published 01 Sep 2016
How long has life flourished on our planet? A new studysuggests it could go back more than 3.7 billion years.
In a study published on Wednesday in Nature, a team ofAustralian researchers describe small conical structures that may have beenbuilt by microorganisms less than a billion years after the planet was born.
The work adds to a growing body of evidence that suggestslife has flourished on Earth since its infancy.
“If these really are the figurative tombstones of ourearliest ancestors, the implications are staggering,” Abigail Allwood, ageologist at the Jet Propulsion Laboratory in La Canada Flintridge, California,wrote in a commentary.
The search for the earliest signs of life on our planet hastaken many different forms. Some researchers scour ancient minerals forchemical signatures that likely have a biological origin. Others have lookedfor physical remnants left behind by the planet’s earliest organisms.
In this study, the research team examined recently exposedrocks from the Isua Greenstone Belt in southwestern Greenland, which has someof the oldest rocks on the planet, dating back as much as 3.7 billion years.They were looking specifically for stromatolites, structures produced bymicroorganisms that trap and bind sediment.
As it turns out, they may have found some. After crackingopen rocks from this area, the researchers report the discovery of stromatolitesfrom two sites where the rocks have remained relatively undisturbed forbillions of years. Further analysis revealed that the structures likely emergedin a shallow marine environment.
“Seeing stromatolites in such a setting would hardly be surprising,if the rocks were half a billion years younger,” Allwood wrote.
But because they are so old, formed less than a billionyears after the birth of the planet, the research team lead by Allen Nutman ofthe University of Wollongong in New South Wales, Australia, will have to workhard to convince other scientists that the structures really do constituteevidence of early life.
In the absence of organic or cellular remains, the authorspoint to four clues that suggest the small mounds were built by ancientorganisms.
These include the conical shape of the structures, a layeredinternal structure, and the fact that sedimentary layers between the conesappear to have formed as sediment piled up against the cones as they stuck outof the sea floor.
They also note a difference in abundance of both titaniumand potassium between the stromatolites and the surrounding rock.
“These four pieces of evidence are not as clear cut as you’dideally want for such an extraordinary claim,” Allwood said. “Nonetheless, theIsua structures are clearly not folds or dewatering structures.”
She said it is certainly possible that they are biological,but said she cannot absolutely refute the possibility that they formed bylocalized mineral precipitation from seawater.
“If we found these on Mars, would we plant a flag anddeclare that we had found life on Mars? I think not, but we would definitelyget very excited and continue looking around for more information,” she said.“And I suspect that’s exactly what will happen in Isua.”