Oldest Life On Earth 'Actually Just Rocks'

oldest life
Photograph of the putative stromatolitic structures in outcrop (arrows). Abigail Allwood

Two years ago, scientists announced they had found what could be the earliest life on Earth. They had found evidence of microbial structures that appeared to be at least 3.7 billion years old—and potentially even older. The discovery had huge ramifications for life on Earth. It showed the first organisms had managed to take hold in a relatively short amount of time after the planet formed 4.5 billion years ago.

But another team of researchers has now questioned the original findings. They believe the fossils are actually just rocks.

In a study published in Nature Abigail Allwood and colleagues from NASA's Jet Propulsion Laboratory have reassessed the rocks, which were found in Greenland, and concluded their shape, orientation and chemical composition do not fit with the idea they are biological in origin.

They find the 3D view of the 'fossils' appears to fit better with the idea they are the shape they are because of natural processes that took place after the rocks were buried—not because of microbial structures embedded in them.

Concluding, they write: "The inherent attributes of the structures, their geological setting in a fold hinge, the deformation fabrics observed in the host rock, and the shape and alignment of the structures within the overall rock fabrics—all indicate non-biological origins."

The team said that while it is reasonable to have interpreted the rocks as being the fossils of early life, "we believe that the current evidence does not support the interpretation of these structures as 3,700-million-year-old stromatolites."

In a News & Views article about the study, Mark van Zuilen, from Paris' Diderot University, said both interpretations of the ancient rocks are important to future study. "The rocky outcrop on Greenland has not been discovered for long, and few researchers have studied this rock in relation to its geological surroundings," he said. "Future research might lead to a firm understanding of the primary versus secondary processes that shaped this rock. Clearly, the work of both Nutman et al. and Allwood et al. will form the basis for the interpretation of other possible stromatolites in the ancient rock record."

The question of when life first appeared on Earth began is important as it helps us understand how it emerged and evolved. It also has big implications for the study of life on other planets—if life took hold less than a billion years after the planet formed, then why wouldn't it appear on other planets too?

"The investigation of the structures of the Isua supracrustal belt serves as a cautionary tale in the search for signs of past life on Mars, highlighting the importance of three dimensional, integrated analysis of morphology, rock fabrics and geochemistry at appropriate scales," Allwood and colleagues conclude.