April 25 (UPI) -- Researchers have discovered fungus-like fossils in rocks estimated to be 2.4 billion years old. The fossils could represent the world's oldest fungus -- 2 billion years older than the next-oldest fungus specimen.
If confirmed, the discovery could force scientists to rethink the timing of early evolution on Earth.
The fossil patterns were discovered in rock samples recovered from basaltic rock in South Africa. The rocks were formed by lava flowing beneath the sea bed.
"The deep biosphere -- where the fossils were found -- represents a significant portion of the Earth, but we know very little about its biology and even less about its evolutionary history," lead researcher Stefan Bengtson, of the Swedish Museum of Natural History, told BBC News.
The newly discovered fossils look like tangled thread and resemble younger fungi fossils found on dry land.
Cavities in the ancient rocks suggest the lava from which they were formed was once a conduit for escaping gas bubbles -- bubbles that might have sustained early life forms.
"Fungi in this environment most probably lived in symbiosis with microbes utilising chemically stored energy for their metabolism," Bengtson said. "They may not even have needed free oxygen."
Bengtson and his colleagues detailed their discovery in the journal Nature Ecology and Evolution.
As expected, at least a few scientists are dubious of the discovery, which challenges a number of assumptions about the emergence of early life on Earth.
"[The discovery], if accurate, would be surprising as it would significantly precede fossil evidence and molecular clock analysis for the origin of eukaryotes, much less the origin of fungi," Andrew H. Knoll, a professor of natural history at Harvard University, told Seeker.
Bengtson acknowledges that the fossils could represent a simpler life form -- an extinct eukaryote lineage or giant prokaryote.
"This is why we call the fossils 'fungus-like' rather than 'fungal,'" Bengtson said. "We have been careful to point out that the filaments we see are very simple."