Life is probably 3.7 billion years old, suggests a new study by Australian researchers. Small conical structures may have been created by microorganisms just a billion years after the planet was born.
"If these really are the figurative tombstones of our earliest ancestors, the implications are staggering," Abigail Allwood, a geologist at the Jet Propulsion Laboratory in La Cañada Flintridge, wrote.
Examining some of the oldest rocks on the planet among the recently exposed ones from the Isua Greenstone Belt in southwestern Greenland, scientists find that they go back to about 3.7 billion years. Experts were searching for stromatolites or structures created by microorganisms that also captured sediment.
Scientists cracked open rocks and found stromatolites in a couple of sites in which the rocks were undisturbed for billions of years and emerged in 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.
The age of the rocks makes it tougher for the research team led by Allen Nutman of the University of Wollongong in New South Wales, Australia, to explain why they contain signs of early life.
As there were no organic or cellular remains, the authors pointed to four clues suggesting that the small mounds had been created long ago. These included "the conical shape of the structures, a layered internal structure, and the fact that sedimentary layers between the cones appear to have formed as sediment piled up against the cones as they stuck out of the sea floor."
"These four pieces of evidence are not as clear cut as you'd ideally want for such an extraordinary claim," Allwood said. "Nonetheless, the Isua structures are clearly not folds or dewatering structures."
"If we found these on Mars, would we plant a flag and declare that we had found life on Mars? I think not, but we would definitely get very excited and continue looking around for more information," she said. "And I suspect that's exactly what will happen in Isua."
The study was published in Nature.
