An international team of scientists in southern China has accidentally discovered the oldest terrestrial fossil ever found, about three times older than the oldest known dinosaur.
Investigations are still ongoing and observations need to be verified independently, but the international team argues that the long filamentous fingers of this ancient organism look very much like fungi.
Either way, the eukaryote appears to have fossilized on land about 635 million years ago, just as the earth recovered from a global ice age.
During this massive icing event, our planet looked like a huge snowball, the oceans of which sealed more than a mile of solid ice from the sun. And then, in a geological ‘flash’, our world began to thaw inexplicably, allowing life to thrive on land for the first time.
Fungi were perhaps one of the first life forms to colonize that fresh space. The date of this new microfossil certainly supports the emerging idea that some fungi-like organisms swelled the oceans for life on land even before plants.
In fact, this transition could help our planet recover from such a catastrophic ice age.
“If our interpretation is correct, it will be helpful to understand the palaeoclimatic change and early life evolution,” says geobiologist Tian Gan, of Virginia Tech College of Science.
Today, the early evolution of fungi remains a major mystery because these organisms do not fossilize easily without bones or shells. Not too long ago, many scientists did not even think it was possible that fungi could last that long.
The genome of contemporary fungi suggests that their common ancestor lived more than a billion years ago and branched out from animals at that time, but unfortunately there may be 600 million years of interruption before the first obvious fungi fossil in our reports appear.
In recent years, a stream of intrigue and controversial discoveries has helped bridge the gap.
In 2019, scientists reported the discovery of a fungal-like fossil in Canada, which fossilized a billion years ago in an estuary. The implications were great – namely that the common ancestor of fungi could have existed much earlier than the common ancestor of plants.
In 2020, a similar fossil was found in the Democratic Republic of the Congo with a similar type of fungus, and it was fossilized in a lagoon or more between 810 and 715 million years ago.
There is still controversy over whether or not these ancient organisms were actually fungi, and the new microfossil found in China will undoubtedly spark similar debates. After carefully comparing the organism’s characteristics with other fossil and living life forms, the authors identify that it is a eukaryote and ‘probable fungi’.
“We would like to leave things open for other possibilities, as part of our scientific investigation,” says Virginia Tech geoscientist Shuhai Xiao.
“The best way to put it is that we may not have rejected that it is fungi, but that it is the best interpretation we have at the moment.”
That said, the new discovery provides more evidence that fungal organisms may have previously had plants on land.
“The question was earlier: ‘Were there fungi in the terrestrial sphere before the emergence of land plants,'” Xiao explains.
“And I think our study suggests yes.”
The next question is: How did those fungi survive?
Today, many species 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 sticky organic matter for carbohydrates.
Because of this relationship, plants and fungi were thought to emerge together to help populate the country. But the oldest terrestrial plant fossil dates only 470 million years ago.
The recently excavated fungal microfossil is much older than this and was found hidden in the small cavities of limestone-doloste rocks, located in the Doushantuo Formation in southern China.
The rock in which the fossil was found was apparently deposited about 635 million years ago after our snowball melted Earth. After the authors were first open to the elements, they suspected that carbon cement had begun to fill the cavities between the limestone sheets, possibly burying the microorganisms living in these bubbles.
These fungi-like life forms could even occur in other terrestrial microorganisms, which were also widespread at the time, such as cyanobacteria or green algae.
If fungal-like animals were equally ubiquitous, it is possible that these life forms helped accelerate the chemical weathering, which produces phosphorus in the ocean and causes a wave of bioproductivity in the marine environment.
On land, they might have helped dig up clay minerals for the carbon sequestration in the earth’s soil, create a fertile environment for plants and animals, and possibly change the atmosphere of our planet.
“Thus,” the authors conclude, “the Doushantuo fungal microorganisms, as cryptic as they were, may have played a role in catalyzing atmospheric oxygenation and biosphere evolution in the aftermath of the terminal Cryogenian global glaciation.”
The study was published in Nature communication.