It’s old. Really, really old.
A fossil from Western Australia, discovered by a team of Chinese scientists from Fujian Normal University, has been confirmed as the oldest known slime mold on the planet, according to a recent study published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
This confirms that slime has been around on Earth for a very, very long time, specifically 2 billion years, according to a recent reassessment of fossil evidence.
The ancient fossil, Myxomitodes stirlingensi, is a hairpin-shaped trace of biological activity discovered in the rocks of the Stirling Range, a mountain region some 200 miles southeast of Perth.
“They have been interpreted as trails of metazoan animals and often as marine organisms,” said Retallack, who is the director of the Condon Fossil Collection at the Museum of Natural and Cultural History. “Though they resemble animal trails, they probably were not. Slime molds make similar trails but lack any animal organization: no mouth, no gut, no anus, no nerves, no veins. And we are seeing these fossils at the surface of ancient terrestrial soils, making them additional evidence of life on land during the Paleoproterozoic Period.”
The fossil has long sparked controversy among experts who have debated about its exact age, specific lifeform it represents, as well as the paleoenvironment it inhabited.
Although slime molds are not themselves multicellular organisms, the researchers have explained that they might hold important clues about how multicellular organisms evolved on Earth.
“Myxomitodes were amoebae that live dispersed in soil, but these traces of their movement demonstrate that they could coalesce into a slug that wandered over the soil as a unit, possibly to sense better feeding opportunities or a place to sporulate, and then disaggregate once again into single cells,” Retallack said.
“This may demonstrate an early stage in the evolution of multicellular creatures, bridging the gap between microbes and more complex life forms.”
This fossil, however, isn’t the oldest known trace of life forms on Earth.
The earliest time that life forms appeared on the planet was most likely 3.77 billion years ago, possibly as early as 4.28 billion years, or even 4.5 billion years ago, not long after the oceans formed.
According to scientists, the earliest direct evidence of life on Earth are microfossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.