A new study led by a University of Oregon geologist might push back the date when life made its way onto dry land.
Gregory Retallack and colleagues have published evidence of urn-shaped fossils from South Africa found in a 2.2-billion-year-old paleosol, or an ancient soil that has turned to rock. The study appears in the September issue of the journal Precambrian Research.
Current scientific consensus says plants got their foothold on land around 450 million years ago, and there is other fossil evidence dating to more than 530 million years ago (including research on Australian fossils published by Retallack in the journal Nature in 2012).
Chemistry of ancient rocks also might suggest that microbial life was attempting to ooze its way onto land billions of years ago.
However, signs of life before 542 million years ago are rare, and scientists differ on how to interpret them, according to a 2012 editorial in Nature.
Enter Retallack’s uber-ancient, match-head-sized fossils, Diskagama buttonii.
These fossils were not plants nor animals but a simpler form of life, resembling a genus of modern soil fungi called Geosiphon, which play host to symbiotic cyanobacteria (together, they form a lichen).
Cyanobacteria are photosynthetic microbes often credited for changing Earth’s early atmosphere by pumping out oxygen as a byproduct of their photosynthesis.
“There is independent evidence for cyanobacteria, but not fungi, of the same geological age, and these new fossils set a new and earlier benchmark for the greening of the land,” Retallack said in a statement. “This gains added significance because fossil soils hosting the fossils have long been taken as evidence for a marked rise in the amount of oxygen in the atmosphere at about 2.4 billion to 2.2 billion years ago, widely called the Great Oxidation Event.”
Retallack, a professor of geological sciences and co-director of paleontological collections at UO Museum of Natural and Cultural History, and fellow researchers were able to distinguish D. buttonii as fossils from other rock features and reconstruct their physical appearance by using X-rays from a particle accelerator at Lawrence Berkeley National Laboratory in California.
They look like hollow urns with a cup at one end and a tail at the other.
David Craig, chairman of Willamette University’s biology department, said he was excited by the research for how it raises questions about the origins and diversification of life and pushes the boundaries of conventional knowledge.
“It’s on the horizons of what we can know and not know, and that’s pushed back all the time by new technology and new and creative ways of people taking and looking at data,” said Craig, who is not connected to Retallack’s study.
Craig also said that Precambrian Research is a lower-ranking scientific journal compared with Nature or Science, meaning the evidence presented to gain publication might be less stringent. However, it is peer reviewed.
Meanwhile, another aspect of D. buttonii that Retallack and colleagues noted was that it could be a candidate for the oldest known eukaryote.
Eukaryotes are organisms whose cells have nuclei and other complex structures that are enclosed in membranes. Fungi are a type of eukaryotes, as are humans.
So, say hello to your little, very distant, possible land-lovin’ cousin.