No record at the Olympics was broken quite like this one. The discovery of 3.7 billion-year-old microbial structures in Isua, Greenland, extends the fossil history of Earth by 220 million years.
In Nature, the University of Wollongong's Professor Allen Nutman describes a set of wavy lines 1 to 4 centimeters (0.4 to 1.6 inches) high found in metamorphic rocks in southwest Greenland. Nutman identifies these as stromatolites, the planet's most ancient type of fossils. The site is one of two where the oldest rocks on Earth survive; the specific site has been dated to 3.7 billion years old.
Molecular clocks tracking the time since living species shared a common ancestor suggest life is older than 4 billion years. Nutman has previously found evidence of carbon dioxide sequestration, suggestive of life, in rocks of the same age. Nevertheless, until Nutman's new discovery, the oldest fossils were from the 3.48 billion-year-old Dresser Formation in Western Australia. The find is powerful confirmation for the theory life appeared almost as soon as Earth was cool enough to support it.
“We know very little about the life forms that made these at this point,” Nutman told IFLScience. “These aren't fossils in the way most people think. They are constructs made by microscopic life, communities of single-celled organisms.” He added that he is working on a project that “may tell us something about the metabolism” of the microbes involved, but this is yet to produce results.
In the meantime, Nutman's confidence that the lines are a product of life, rather than a geological formation, rests on several pieces of evidence. “We examined the discovery with a stromatolite expert, who has a series of criteria to tick off,” Nutman said. “These include the general shape, the relationship with adjacent rocks, and the chemistry.”
Close up of the Isua stromatolite (a) and (b) compared to specimens from Western Australia (c) and (d). The lens cap in blue at the bottom is 4cm (1.6in) in diameter. Nutman et al/Nature