Fungus-Like Forms Found in 2.4 Billion-Year-Old Rocks
An international team of researchers, including scientists from the Swedish Museum of Natural History, Stockholm University and the University of California, have identified microscopic structures found in tiny bubbles and pores in ancient basalt that resemble fungi. If these fungi-like structures are indeed Palaeoproterozoic remnants of members of the Kingdom Fungi, then this discovery could push back the date for the oldest fungi by between 1,000 and 2,000 million years.
Thin Sections of the Ongeluk Basalt Showing Evidence of Mycelium
Picture credit: Nature, Ecology and Evolution (Swedish Museum of Natural History)
Over the last few decades, cores drilled deep into the seabed and other exploration techniques utilised to build knowledge of the biota present in oceanic sediments and crustal rocks have revealed that many different types of fungi thrive in these environments. The fossil record of fungi is extremely intermittent and the identification of possible fungal remnants in the fossil record is controversial to say the least, (look up the Devonian Prototaxites for further details).
The Fossil Record of Fungi
However, many geologists and palaeontologists have proposed that the fossil record for such extremophiles does date back to at least the Early Devonian, a time when primitive plants and fungi were beginning to diversify and radiate in terrestrial environments. Drill cores taken from the Ongeluk Formation in South Africa show microscopic signs of filamentous fossils in vesicles and fractures. The filaments form mycelium-like structures growing from a basal film attached to the internal rock surfaces and they look very similar to the structures attributed to fungi found in rocks which are hundreds of millions of years younger.
The Ongeluk fossils, are two to three times older than current age estimates of the Kingdom Fungi. Unless they represent an unknown branch of fungus-like organisms, which are new to science, the fossils imply that the fungal clade is considerably older than previously thought, and that fungal origin and early evolution may lie in the deep ocean rather than in terrestrial environments.
The Ongeluk discovery suggests that life has inhabited deep sea oceanic rocks for more than 2.4 billion years.
The Impact on Eukaryotes
The jumbles of tangled threads, which are only a few microns across, if they are fungi, belong to the Eukaryote Domain (Eukarya), a diverse group containing at least four Phyla and some 6,000 species, (fungi include the familiar mushrooms and toadstools plus yeasts and moulds). Eukaryotes have cells that are complex with a distinct nucleus protected by a membrane. Animals and plants are also Eukaryotes and the discovery of such ancient life forms, preserved in ocean rocks has implications for the early history of the whole of the Eukarya, as well as potentially, pushing back the date for the evolution of the first fungi to around 2.4 billion-years-ago.
Commenting on the significance of this research, lead author of the scientific paper, Stefan Bengtson (Department of Palaeobiology and Nordic Center for Earth Evolution, Swedish Museum of Natural History), stated:
“The deep biosphere [where the fossils were found] represents a large portion of the Earth, but we know very little about its biology and even less about its evolutionary history.”
The Professor added, that there was a clear possibility that these fossils represent the world’s oldest fossil fungi, much older than anything else known to the scientific community.
He went onto state:
“If they are not fungi, they are probably an extinct branch of Eukaryotes or even giant Prokaryotes.”
The Impact on the Hunt for Life on Other Planets
A spokesperson from Everything Dinosaur commented that if these fossils represent fungi occupying gas bubbles in lava that form rocks in the seabed, it demonstrates how organisms can survive in extreme habitats. Tests have indicated that the rocks where the structures were found could have been as hot as 250 degrees Celsius and these lifeforms would have had to survive without sunlight and cope with immense pressure.
If the fossil record for such fungi is extended by billions of years on our own planet, then it raises the intriguing possibility that such life forms may well have evolved and if they did, they probably still exist in extreme environments elsewhere in our solar system. The watery environment trapped under the ice of Saturn’s moon Enceladus could harbour the sort of conditions where organisms such as these could still thrive.
Saturn’s Icy Moon Enceladus – Perhaps Home to Marine Crustal Fungi?
Picture credit: NASA
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