An international team of scientists in South China suddenly discovered the oldest terrestrial fossil ever discovered, about three times older than the oldest known dinosaur.
Investigations are still ongoing and opinions need to be independently verified, but the international team argues that long fingers resembling the thread of this ancient organism look very much like a fungus. .
Whatever it is, the eukaryote appears to have been fossilized on land around 635 million years ago, just as the Earth was recovering from a global ice age.
At this major glacial event, our planet was like a giant snowball, its oceans sealed from the Sun more than a kilometer (0.6 miles) of hard ice. And then, in a geological ‘flash’, our world began to melt unsustainably, allowing life to thrive on land for the first time.
Fungi may have been among the first forms of life to colonize this new place. The date of this new microfossil certainly supports the emerging view that some fungus-like organisms blackened the oceans for land life even before plants.
In fact, it was perhaps this transition that helped our planet recover from such a catastrophic ice age.
“If our explanation is correct, it will be helpful to understand the paleoclimate change and early life evolution,” says geologist Tian Gan, of Virginia Tech College of Science.
Today, the early evolution of fungi remains a great mystery, largely because without bones or shells, these organisms do not fossil easily. Until recently, many scientists did not even believe that fungi could survive so long.
Today’s species of fungi show that their common ancestor lived more than a billion years ago, extinct from animals at that time, but unfortunately, a 600 million year break could be over. existed before the first apparent fungal fossils appeared in our records.
In the last few years, a stream of interesting and controversial discovery has helped fill that gap.
In 2019, scientists reported the discovery of a fungal-like fossil in Canada, which had fossilized billions of years ago in an estuary. The effect was enormous – that is, the ancestor of a common fungus was probably around much earlier than the common ancestor of plants.
In 2020, similar fungal-like fossils were discovered in the Democratic Republic of the Congo, and fossilized in a sea or lake between 810 and 715 million years ago.
There is still controversy as to whether or not these ancient organisms were fungi, and the new microfossil found in China will no doubt provoke a similar debate. After carefully comparing the organism’s characteristics with other fossils and living life forms, the authors identify it as a eukaryote and a “most likely fungus”.
“We want to leave things open for other opportunities, as part of our scientific research,” says geologist Shuhai Xiao of Virginia Tech.
“The best way to put it is, we may not have agreed that they are fungi, but they are the best explanation we have right now.”
That said, the new find provides further evidence that land-based plants may have contained fungus-like organisms.
“The question used to be: ‘Were there fungi in the land before terrestrial plants arose’,” Xiao explained.
“And I think our study suggests that.”
The next question is: How did these fungi survive?
Today, many species of terrestrial fungi are incapable of photosynthesis. Therefore, they depend on each other’s relationship with plant roots, exchanging water and nutrients from rocks and other difficult organic matter for carbohydrates.
Because of this relationship, plants and fungi were thought to come together to help build the soil. But the oldest land plant fossil dates back to 470 million years ago.
The microfossil-like fungus recently discovered is much older than that and has been found hidden inside small caves of limestone rocks, located in the Doushantuo Formation in South China.
The rock in which the fossil was found appears to have been deposited about 635 million years ago, after our snowball Earth melted. Once exposed to the elements, the authors suspect that carbonate cement began to fill the caverns between the sheets of limestone, possibly including the microorganisms that live inside these bubbles.
These fungal-like life forms may have even adopted other terrestrial microorganisms, which were common at the time, such as cyanobacteria or green algae.
If fungus-like animals were equally ubiquitous, it is possible that these life forms would help accelerate chemical weather, deliver phosphorus to the oceans and provide a wave of biogenesis in the marine environment.
On land, they may have even helped discover clay minerals for carbon sequestration in Earth’s soil, creating a fertile environment for plants and animals and possibly altering the very atmosphere of our planet.
“Thus,” the authors conclude, “the microorganisms of the Doushantuo fungus, however lame, may have played a role in capturing atmospheric oxygenation and evolution biospheric after the last Cryogenian global glaciation. “
The study was published in Nature Communication.