An international team of scientists from southern China accidentally discovered the oldest terrestrial fossil ever found, about three times older than the oldest known. dinosaur.
Investigations are still ongoing and sightings will need to be verified independently, but the international team argues that the long, wiry fingers of this ancient organism closely resemble mushrooms.
Regardless, the eukaryote appears to have fossilized on Earth around 635 million years ago, just as Earth was recovering from a global ice age.
During this massive glacial event, our planet looked like a huge snowball, with its oceans sealed from the Sun by more than a kilometer (0.6 miles) of solid ice. And then, in a geological “lightning”, our world began to inexplicably thaw, allowing life to flourish on earth for the first time.
Fungi may have been among the first forms of life to colonize this new space. The date of this new microfossil certainly supports the emergence
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idea that some mushroom-like organisms left the oceans to live on earth even before plants.
In fact, this transition could have been what helped our planet recover from such a catastrophic ice age.
“If our interpretation is correct, it will be useful in understanding paleoclimatic change and the early course of life.” says geobiologist Tian Gan of Virginia Tech College of Science.
Today, the early evolution of fungi remains a great mystery, in large part because without bones and shells, these organisms do not fossilize easily. Not long ago, many scientists didn’t even think it was possible that mushrooms last that long.
The genome of modern fungi suggests that their common ancestor lived over a billion years ago, branching out from animals back then, but sadly there could be a 600 million break. years before the first obvious mushroom fossil appeared in our records.
In recent years, a series of intriguing and controversial discoveries have helped bridge this gap.
In 2019, scientists reported the discovery of a mushroom-like fossil in Canada that had fossilized a billion years ago in an estuary. The implications were enormous, meaning that the common ancestor of fungi may have existed long before the common ancestor of plants.
In 2020, a similar mushroom-like fossil was found in the Democratic Republic of the Congo, and it was fossilized in a lagoon or lake between 810 and 715 million years ago.
Controversy persists as to whether these ancient organisms were really fungi, and the new microfossil found in China will no doubt stimulate a similar debate. After carefully comparing the characteristics of the organism with other fossils and living forms of life, the authors identify that it is a eukaryote and a “probable fungus”.
“We would like to leave things open to other possibilities, as part of our scientific research,” says geoscientist Shuhai Xiao of Virginia Tech.
“The best way to put it is that we may not have disapproved of the fact that they are mushrooms, but they are the best interpretation we have yet.”
That said, the new discovery provides further evidence that fungal-like organisms may have preceded land plants.
“The question was,” Were there fungi in the earthly kingdom before the emergence of land plants? “Xiao explains.
“And I think our study suggests it does.”
The next question is: how did these fungi survive?
Today, many species of terrestrial fungi are unable to photosynthesize. As such, they depend on a mutualistic relationship with the roots of plants, exchanging water and nutrients from rocks and other hard organics for carbohydrates.
Because of this relationship, it was believed that plants and fungi appeared together to help populate the earth. But the oldest terrestrial plant fossil is only 470 million years old.
The recently unearthed mushroom-like microfossil is much older than this and has been found hidden in small cavities of dolomitic limestone rocks, located in the Doushantuo Formation in southern China.
The rock in which the fossil was found appears to have been deposited around 635 million years ago, after our snowball Earth melted. Once opened to the elements, the authors suspect that the carbonated cement began to fill the cavities between the limestone sheets, eventually burying the microorganisms that live in these bubbles.
These fungal-like life forms could even have lodged with other terrestrial microorganisms, also prevalent at the time, such as cyanobacteria or green algae.
If mushroom-like animals were also ubiquitous, it’s possible that these life forms helped accelerate chemical weathering, deliver phosphorus to the seas, and spark a wave of bioproductivity in the marine environment.
On earth, they could even have helped unearth clay minerals for carbon sequestration in Earth’s soil, creating a fertile environment for plants and animals and eventually altering the very atmosphere of our planet.
“Thus,” the authors conclude, “Doushantuo mushroom-like microorganisms, cryptic as they are, may have played a role in catalysing atmospheric oxygenation and biospheric evolution after the Global Ice Age. terminal. “
The study was published in Nature’s communications.
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