New Delhi: Researchers on Monday, accidentally stumbled upon what is being called the oldest fungi ever discovered. Found in South Africa by a margin of 1.2 billion years, the new discovery has raised questions on the evolution of these organisms.
The fungi, which can neither be considered flora nor fauna, have slender filaments that are bundled together like brooms.
The 2.4 billion-year-old microscopic creatures could also be the earliest known specimens of the branch of life to which humans belong, researchers reported in the journal Nature Ecology & Evolution.
Up to now, the first fossil trace of eukaryotes – the "superkingdom" that includes plants, animals and fungi, but not bacteria – dates to only 1.9 billion years ago. Earth itself is about 4.6 billion years old.
According to BBC, the find suggests that fungi arose not on land but in the deep sea. If not a fungus, the organism could be from an extinct branch of life that has not been described before.
Lead researcher Prof Stefan Bengtson of the Swedish Museum of Natural History explained how previously, scientists may have been looking in the wrong place for the oldest fossil fungi – on land or in shallow seas rather than in the deep sea.
It has long been assumed that fungi first emerged on land, but the newly-found organisms lived and thrived under an ancient ocean seabed, tucked in the crevices of volcanic rock.
The ancient fungus-like life forms, found in fossilised gas bubbles 800 metres (2,600 feet) underground in South Africa's Northern Cape Province, are remarkable not just for their age but their origin, the researchers said.
Nobody was looking for them, explained co-author Birger Rasmussen, a geology professor at Curtin University in Bentley, Australia who was examining lava samples from the Ongeluk Formation to determine their age.
"My attention was drawn to a series of petrified gas bubbles, and when I increased the magnification of the microscope, I was startled," he recalled.
The bubbles were "filled with hundreds of exquisitely preserved filaments that just screamed 'life'," he wrote by email.
The plot thickened when Rasmussen realised that the surrounding lava was not 2.2 billion years old, as previously thought, but 2.4 billion years old.
That extra 200 million years was significant because it straddles a critical threshold in Earth's geological history called the Great Oxidation Event – a rapid and massive outpouring of oxygen into the atmosphere.
The new dating meant that not only had these fungus-like creatures lived in a dark and cavernous world devoid of light, but they also lacked oxygen.
"This would have tremendous implications for the lifestyle of the early ancestors of eukaryotes and fungi," Rasmussen added.
For many years, fungi were grouped with, or mistaken for plants. Not until 1969 were they officially granted their own "kingdom", alongside animals and plants, though their distinct characteristics had been recognized long before that.
Yeast, mildew and molds are all fungi, as are many forms of large, mushroom-looking organisms that grow in moist forest environments and absorb nutrients from dead or living organic matter.
Earlier research has turned up evidence that gas bubbles in lava below the bottom of the sea provided living space for fungi as far back as 50 million years.
"What we have now found is that such a habitat existed already more than two billion years ago – at a time when fungi were not thought to have yet existed," Bengtson told AFP.
Fungi in this environment most probably live in symbiosis with microbes, using chemically stored energy for their metabolism, added co-author Magnus Ivarsson, an expert on these hidden worlds.
"They may not even have needed free oxygen."
Scientists not involved in the study said its was potentially paradigm shifting, but must be bolstered by further research.
The discovery "challenges current thinking about when and where eukaryotes evolved," Nicola McLoughlin, a professor at Rhodes University in Grahamstown, South Africa, commented, also in Nature Ecology & Evolution.
It "raises the question of whether we have been looking in the wrong place for the earliest eukaryotes and fossil fungi in particular."
(With AFP inputs)