The scientific method is a beautiful thing. For those of you who may not be familiar with it, this multi-step empirical process allows the scientific community to not only come up with some pretty bold findings, but for others to test, replicate, and potentially disprove those outcomes.
Two years ago, a team of scientists announced they had found the world’s oldest fossils preserved in stone in Greenland. In the journal Nature, the Australian-based team claimed these odd structures were once microbes living on the ancient seafloor. At a mere 3.7 billion years old, it would mean that life had formed much quicker and easier than we had originally thought.
At the time, NASA astrobiologist Abigail Allwood was so optimistic about the findings that she wrote a letter supporting them. Soon after, though, she felt something might be a bit off. So, she packed her bags – and a few X-ray instruments meant for Mars – and headed to Greenland with a team of researchers.
Together, they created a 3D chemical map of the “fossil” structures, which she argues don’t have the same chemical signature of fossilized life. If these remains were in fact stromatolites, single-celled microbes, they would have grown upward from the seafloor and situated themselves in a gooey mucus that accumulates minerals from the seawater, which then layer, harden, and fossilize. Ultimately, they form in different sizes but always take on a cone, column, or dome shape.
“By contrast, when viewed orthogonally the rock shows flat, even layering without any stromatolites, bumps or irregularities,” wrote Allwood in her letter also published in Nature. She continues that when her team cut into the outcrop, samples were not a cone, but rather a ridge shape that went several inches deep into the rock – a product more likely from geological than biological processes.
The Australian scientists who worked on the first paper maintain their findings are still legitimate.
“We expected that our publication would generate new investigations and looked forward to the results,” Vickie Bennett, who worked in Greenland on the original investigation, told The Atlantic. “But [Allwood’s] cursory investigation, based on a less-than-one-day field trip to the outcrops, which were partially covered in snow at the time, only serves to confuse our earlier work.”
She and study co-authors maintain Allwood focused on an outer, more deformed area rather than the more-intact central areas. “They basically did not look at the same rocks,” said Bennett.
Allwood argues the area she studied was less than a meter away from the original – and her single day there was “enough to disprove them”, particularly when they analyzed the sample back in the lab.
Not only does it have implications for our understanding of how life evolved on Earth, but it serves as a “cautionary tale in the research for signs of past life on Mars,” said Allwood, who is an investigator on NASA's Mars 2020 mission. It reminds us of the need to highlight “the importance of three-dimensional, integrated analysis of morphology, rock fabrics, and geochemistry at appropriate scales.”
2