"In their defense," he adds, "fieldwork in Greenland is very difficult to do, but in our defense, this is why having good weather and good exposure has allowed us to see everything quite clearly. . "
In her lab, she and her colleagues analyzed the chemical composition of the rock of Greenland and found more evidence to support their interpretation. Real stromatolites, like those in Australia, should have inner layers, but those of Greenland do not. Instead, they are almost pure silicon inside, with edges of dolomite minerals that separate them from the overlying rock. These facilities were not the work of microbes, says Allwood. Instead, they were created when fluids containing dolomite minerals filtered into silicon and crystallized pieces, "like chocolate dipped in a vanilla sponge."
Nutman claims that the inner layers, although not as well preserved as those of younger Australian stromatolites, are there in other Greenland samples. And it indicates the distinct chemical of the cones. They have lower titanium and potassium concentrations than the surrounding rocks, and also unusual levels of yttrium and other rare elements that are indicative of seawater. These signatures suggest that the cones were not just random pieces of rock that were bent into exaggerated shapes, but the work of marine microbes that tore away fragments of minerals from the ocean.
Not like that, says Allwood. Titanium and potassium mean nothing: they are also impoverished in other parts of the outcrop that are outside the cones. And as far as yttrium and other rare elements are concerned, a more detailed analysis shows that they are concentrated in microscopic fragments of mica and quartz minerals that probably formed in the rocks at later stages of their existence. "It has nothing to do with biology," says Allwood. (Nutman does not find this plausible, and notes that other rocks in the same area do not have the same signature. "We support our interpretation," he says.)
Phoebe Cohen, a paleontologist at Williams College who was not involved in any study , thinks that Allwood's interpretation is more likely. "Exceptional claims require exceptional data to support them, and while the original [team] did a good job collecting evidence for their request, it was not entirely convincing," he says. "This follow-up study is exactly what I would have hoped for, I am sure this will not be the last time a document of" older life's proof "is denied by further research, but I do not see it. now to be convinced one day! "
Bennett argues that the controversy changes little, since there are other lines of evidence that indicate the existence of life more than 3.6 billion years ago. "It's becoming difficult to dispute the presence of an ancient life from the beginning of rock records on Earth," he says. And again, Allwood is not on agreement. Beyond Australian stromatolites, which are less than 3.5 billion years old, "we have no other unequivocal evidence," he says. "It does not mean that there there were no microbes around, but we can not hang the hat on this fact."