In 2016, a team of Australian scientists revealed they had discovered the world's oldest fossils in an exposed rock formation in Greenland. The creatures revealed in the fossils looked like stromatolites, tiny layered mounds just a few centimeters tall that are known to be formed by photosynthetic microbes living in water, reported New Scientist.
Now, another group of scientists are refuting that claim.
NASA astrobiologist Abigail Allwood traveled to Greenland to analyze the fossils. Allwood discovered that the shape, interior layers and weathering didn't match up with the typical characteristics of stromatolite fossils. A NASA tool was used to study the chemical structure, and the rocks didn't have the chemical makeup of fossils.
Several other experts told The Associated Press (AP) that they support Allwood's findings. But the Australian team led by Allen Nutman at the University of Wollongong stands by their findings and says Allwood didn't test the original specimens from the 2016 study and only took samples from the far ends of the rock formations.
"This is a classic comparing-apples-and-oranges scenario, leading to the inevitable outcome that ours and their observations do not exactly match," the team of Australian scientists said in the statement to AP.
Two years ago, the find was made possible due to expanded ice melt on the Greenland continent, which is exposing rocks that have been buried beneath Greenland's ice for ages. The fossils (or rocks) were found in a region of southwest Greenland called the Isua supracrustal belt, a place that has remained relatively safe from geological processes that churn the crust and renew the Earth's features and bury the record of its history.
"This is one of the extremely few places where this kind of feature could still be preserved in the rock record," explained Nutman.
Stromatolites are fairly complex structures that are still made by microbes today. Their complexity indicates that these were probably not among the first organisms to evolve; they would have been part of a vast biota with a history that stretches back even further than the fossils' 3.7-billion-year-old date suggests. In other words, life would have had to have emerged on Earth even sooner than this for such complicated lifeforms to have evolved.
"What we have in Isua is just a tiny sample of any life that may have been around at that time," said Nutman in 2016. "It would be like going to somewhere on Earth now and picking up some shells from a beach and getting the impression, 'Oh, that's the full diversity of life that is on the planet'."
Editor's note: This article has been updated since it was originally published in August 2016.