An international team of scientists in southern China accidentally discovered the oldest terrestrial fossil ever found, about three times older than the oldest known dinosaur.
Research is ongoing and observations will need to be independently verified, but the international team claims that the long thread-like fingers of this ancient organism look a lot like fungi.
Whatever it is, the eukaryote appears to have fossilized on land roughly 635 million years ago, just as Earth was recovering from a global ice age.
During this enormous Ice Age, our planet looked like a large snowball, the oceans of which were more than a kilometer of solid ice cut off from the sun. And then, in a geological “ flash, ” our world inexplicably began to thaw, allowing life to thrive on land for the first time.
Fungi may have been one of the first life forms to colonize that new space. The date of this new microfossil certainly supports the emerging idea that some fungal organisms have dumped the oceans for life on land, even before the plants.
In fact, this transition could have been the cause of our planet’s recovery from such a catastrophic Ice Age.
“If our interpretation is correct, it will be helpful to understand paleoclimate change and early life evolution,” said Virginia Tech College of Science geobiologist Tian Gan.
Today, the early evolution of fungi remains a great mystery, largely because these boneless or shelled organisms do not fossilize readily. Not long ago, many scientists thought that fungi couldn’t even last that long.
The genome of modern-day fungi suggests that their common ancestor lived over a billion years ago and branched out from animals during that time, but unfortunately there may be a 600 million year pause before the first obvious fungal fossil shows up in our archives.
In recent years, a stream of intriguing and controversial discoveries has helped bridge that gap.
In 2019, scientists reported the discovery of a fungus-like fossil in Canada that had fossilized in an estuary a billion years ago. The implications were enormous – namely, that the common ancestor of fungi may have existed much earlier than the common ancestor of plants.
In 2020, a similar fossil with a similarity to fungi was found in the Democratic Republic of the Congo, and it was fossilized in a lagoon or more between 810 and 715 million years ago.
Controversy still exists as to whether these ancient organisms were actually fungi, and the new microfossil found in China will no doubt spark a similar debate. After carefully comparing the organism’s characteristics to other fossils and living life forms, the authors identify it to be a eukaryote and “likely fungi.”
“We would like to leave things open to other possibilities as part of our scientific research,” said Virginia Tech geoscientist Shuhai Xiao.
“The best way to put it is that we may not have disapproved that they are fungi, but they are the best interpretation we have at the moment.”
That said, the new discovery provides more evidence that fungal organisms may be older than land plants.
“The question used to be, ‘Were there fungi on the land before the emergence of land plants,’” explains Xiao.
“And I think our study suggests yes.”
The next question is: how did those fungi survive?
Today, many types of terrestrial fungi are incapable of photosynthesis. As such, they rely on a mutualistic relationship with the roots of plants, exchanging water and nutrients from rocks and other tough organic matter for carbohydrates.
Because of this relationship, it was thought that plants and fungi emerged together to populate the land. But the oldest fossil of land plants dates back to 470 million years ago.
The recently excavated fungal microfossil is much older than that and was found hidden in the small hollows of limestone dolostone rocks located in the Doushantuo Formation in southern 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 open to the elements, the authors suspected that carbonate cement began to fill in the voids between the limestone slabs, potentially trapping the microorganisms that live in these bubbles.
These fungus-like life forms may even have become chambered with other terrestrial microorganisms, which were then also widespread, such as cyanobacteria or green algae.
If fungal animals were equally ubiquitous, it is possible that these life forms may have helped accelerate chemical weathering, release phosphorus to the seas and spark a surge in bioproductivity in the marine environment.
On land, they may even have helped excavate clay minerals for carbon storage in the Earth’s soil, creating a fertile environment for plants and animals and potentially altering our planet’s atmosphere.
So, the authors conclude, “the Doushantuo fungal microorganisms, cryptic as they may have been, may have played a role in catalyzing atmospheric oxygenation and biospheric evolution in the wake of the terminal Cryogenic Global Ice Age.”
The study is published in Nature Communications.