635 million year old fungal microfossils that saved us from the ice age have been discovered

When you think of fungi, you can be an important ingredient in a recipe, or their incredible ability to break down dead organic matter into important nutrients. But new research by Shuhai Xiao, a professor of geosciences at the Virginia Tech College of Science, and Tian Gan, a visiting Ph.D. student in the Xiao Laboratory, emphasizes another important role that fungi played during Earth’s history: helping the planet recover from an ice age.

A team of scientists from Virginia Tech, the Chinese Academy of Sciences, Guizhou Education University and the University of Cincinnati have discovered the remains of a fungal microfossil that formed about 635 million years ago at the end of an ice age. It is the oldest terrestrial fossil ever found. To put this in perspective, this microfossil is the oldest dinosaurs about three times older.

Their findings were published in 2008 Nature communication on 28 January.

The fossil was found in small cavities in well-studied sedimentary doloste rocks of the Lower Doushantuo Formation in southern China. Although the Doushantuo formation has so far provided an abundance of fossils, researchers did not expect to find fossils to the lower base of the dolostones.

But in all probability, Gan found some long, filamentous filaments – one of the most important properties of fungi.

“It was an accidental discovery,” Gan said. “At that moment, we realized that it could be the fossil that scientists have been looking for for a long time. If our interpretation is correct, it will be useful to understand the palaeoclimatic change and early life evolution.”

This discovery is the key to understanding several turning points in the history of the earth: the Ediacaran period and the terrestrialization of fungi.

When the Ediacaran period began, the planet recovered from a catastrophic ice age, also known as the ‘snowball earth’. At that time, the ocean surfaces were frozen to a depth of more than a kilometer and it was an incredibly harsh environment for almost any living organism, except for a microscopic life that could succeed in it. Scientists have long wondered how life ever became normal again – and how the biosphere could become larger and more complex than ever before.

With this new fossil in hand, Tian and Xiao are certain that these low-profile microscopic cave dwellers played numerous roles in revitalizing the Earth’s environment during the Ediacaran era. The formidable digestive system was one of the role.

Fungi have a rather unique digestive system that plays an even greater role in the cycling of important nutrients. Using enzymes secreted in the environment, soil fungi can chemically degrade rocks and other sticky organic matter, which can then be recycled and exported to the ocean.

“Fungi have a mutualistic relationship with the roots of plants, which helps them to mobilize minerals such as phosphorus. Due to their connection with land plants and important nutrient cycles, native fungi have a driving influence on biochemical weathering, the global biogeochemical cycle, ecological interactions , ”Said Gan.

Although previous evidence states that soil plants and fungi formed a symbiotic relationship about 400 million years ago, this new discovery recalibrated the timeline of the time when these two kingdoms colonized the land.

“The question was earlier, ‘Were there fungi in the terrestrial sphere before the emergence of land plants,'” said Xiao, an affiliated faculty member of the Fralin Life Sciences Institute and the Global Change Center. “And I think our study suggests yes. Our fungal fossil is 240 million years older than the previous record. It is by far the oldest record of terrestrial fungi.”

Now new questions have arisen. Since the fossilized filaments were accompanied by other fossils, Gan will investigate their relationships in the past.

“One of my goals is to limit the phylogenetic affinities of these other species of fossils associated with the fungal fossils,” Gan said.

Xiao is delighted to address the environmental aspects of this micro-organism. Sixty years ago, few people believed that microorganisms, such as bacteria and fungi, could be preserved as fossils. Now that Xiao has seen them with his own eyes, he plans to learn more about how they were frozen in time.

“It is always important to understand the organisms in the environmental context,” Xiao said. “We have a general idea that they live in small cavities in dolostone rocks. But little is known about exactly how they lived and how they were preserved. Why can something like fungi, which have no bones or shells, live in the fossil stock is preserved? “

However, it cannot be said with certainty whether this fossil is a definitive fungus. Although there is a fair amount of evidence behind it, the investigation into these microfossils is ongoing.

“We would like to leave things open for other possibilities, as part of our scientific investigation,” Xiao said. “The best way to put it is that we may not have rejected that they are fungi, but that this is the best interpretation we have at the moment.”

Three different groups and laboratories at Virginia Tech were crucial to the identification and timestamp of this fossil. The Confocal Laser Scanning and Microscopy lab at the Fralin Life Sciences Institute helped Tian and Xiao perform initial analyzes that led to further research at the University of Cincinnati.

The Massey Herbarium of the Department of Biological Sciences, which contains more than 115,000 specimens of vascular plants, fungi, bryophytes and lichen, provided modern fungal samples for comparison with the fossils.

The team called on technicians to perform geochemical analyzes using secondary ion mass spectrometry, which ionizes nanomaterials from small areas that are a fraction of the thickness of a strand of hair, to analyze the isotopic abundance of sulfur-32 and sulfur-34 to understand the fossilization environment.

Advanced computed tomography was crucial to obtain the 3-D morphology of the filaments, which are only a few micrometers thick. And a combination of focused ion-beam scanning electron microscopy and transmission electron microscopy enabled the researchers to cut samples with surgical precision and take a closer look at each nanometer of the filaments.

“It was not a single person or even a single laboratory that did this work,” Xiao said.

Xiao also stressed the importance of interdisciplinary research in this study and many others.

“It is very important to encourage the next generation of scientists to be trained in an interdisciplinary light, because new discoveries are always taking place at the interface of different fields,” Xiao said.