The oldest evidence of land fungus perhaps a very small microfossil 635 million years old found in a cave in southern China.
This remarkable find is too small to be seen with the naked eye and reduces the appearance of land fungi by about 240 million years to a period known as “snowball earthwhen the planet was trapped in ice from 750 million to 580 million years ago.
The presence of land fungus at this critical point may have helped Earth transition from a frozen ice ball to a planet with a variety of ecosystems that could harbor different life forms, scientists wrote in a new study. By breaking down minerals and organic matter, and recycling nutrients in the atmosphere and ocean, ancient fungus could have played an important role in reshaping Earth’s geochemistry, creating more hospitable conditions that paved the way for land plants and animals to eventually emerge and thrive.
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Scientists discovered the petrified thread-like filaments – a trademark of fungal structures – in sedimentary rocks of China’s Doushantuo Formation in Guizhou Province, dating back to the Ediacaran Period (about 635 million to 541 million years ago). Identifying rocks that may contain microscopic fossils takes both luck and skill, said study co-author Shuhai Xiao, a professor of geosciences at Virginia Tech College of Science (VT) in Blacksburgh, Virginia.
“There is an element of serendipity, but there is also an element of experience and expectation. After working with microfossils, you know what kind of rocks to look at,” Xiao told Live Science. For example, rocks must be fine-grained because the fossils are so small. Color can also provide clues; biological carbon in microfossils, fossil-bearing rocks can appear darker than rocks that do not contain fossils.
“But it’s not fault-proof; usually we cut a stone and don’t find anything. There may be a 10% success rate,” said Xiao.
Thin sliced
To find the fossils, the study authors crushed slices of rock thin enough to transmit light no more than 0.002 inches (50 micrometers) thick. Powerful microscopes revealed the fungus’ tiny tendrils, which were only a few micrometers in diameter – about 1/10 the width of a human hair. Under the microscopes, traces of organic carbon in the fossils were darker than the rock around them.
The researchers also used more advanced microscopy to examine the fossils and make digital copies of their structures. Fortunately, many of those structures were “excellently preserved in three dimensions,” lead researcher Tian Gan, a doctoral student at the Chinese Academy of Sciences in Beijing and a visiting scholar at VT, told Live Science in an email.
Those branching filaments told the researchers that the fossils were of biological origin, rather than mineral. While some types of bacteria also produce branches, the closest analogues for these types of filaments are fungus, and tiny spheres in the fossil “ could be interpreted as fungal spores, ” supporting the hypothesis that these microorganisms were a type of fungus, the scientists wrote. . .
Old life
Fossil evidence of the earliest organisms on Earth is exceptionally rare, but this microfossil and other recent finds are helping researchers slowly gather important clues as to when life first appeared.
The oldest evidence of sea fungus, described in 2019 from rocks found in Canada, dates back to about a billion years ago; the oldest forest, described in 2020 from fossilized roots in New York State, is 386 million years old; and the oldest known animal – called a bizarre, oval-shaped creature Dickinsonia – is about 558 million years old (fossils once thought to represent older animals were recently attributed to ancient algae, Live Science reported in December 2020).
Fossilized buildings from Canada built by microbes possibly between 3.77 billion and 4.29 billion years ago, represent one of the oldest possible examples of life on Earth. Other structures preserved in Greenland rock are also believed to be of microbial origin and are 3.7 billion years old. Yet another fossil from Western Australia may contain microbes estimated to be 3.5 billion years old, although some scientists have argued that geothermal activity could have altered the chemicals in the rock to make them look like biological tracks. Live Science previously reported.
Scientists first linked terrestrial fungus to the appearance of land plants, based on fossils from the Rhynie cherts in Scotland that keep plants and fungi together and date back to about 410 million years ago, Xiao said. In those fossils, “plants and fungi have already established some kind of ecological relationship,” he explained.
Fossils of fungi predating the earliest known plants previously hinted that terrestrial fungus first appeared about 450 million years ago, “and now we’re extending that to 635 million years ago,” Xiao said.
The findings were published online Jan. 28 in the journal Nature Communications.
Originally published on Live Science.