Scientists have discovered a “lost world” of ancient organisms in billion-year-old rocks from northern Australia that they say could change the world’s understanding of humans’ earliest ancestors.
The microscopic creatures, known as Protosterol Biota, are part of a family of organisms called eukaryotes and lived in Earth’s waterways about 1.6 billion years ago, according to the researchers.
Eukaryotes have a complex cell structure that includes mitochondria, the cell’s “powerhouse”, and a nucleus, its “control and information centre”.
Modern forms of eukaryotes include fungi, plants, animals and single-celled organisms such as amoebae.
Humans and all other nucleated creatures can trace their ancestral lineage back to the last eukaryotic common ancestors (LECA), which lived more than 1.2 billion years ago.
The new discoveries “appear to be the oldest remnants of our own lineage – they lived even before LECA,” said Benjamin Nettersheim, who completed his PhD at the Australian National University (ANU) and is now based at the University of Bremen in Germany.
“These ancient creatures were abundant in marine ecosystems across the world and probably shaped ecosystems for much of Earth’s history.”
The discovery of the Protosterol Biota is the result of 10 years of work by researchers from ANU and was published in Nature on Thursday.
ANU’s Jochen Brocks, who made the discovery with Nettersheim, said the Protosterol Biota were more complex than bacteria and presumably larger, although it is unknown what they looked like.
“We believe they may have been the first predators on Earth, hunting and devouring bacteria,” the professor said in a statement.
The researchers, from Australia, France, Germany and the United States, investigated fossil fat molecules found inside a rock that had formed at the bottom of the ocean near what is now Australia’s Northern Territory for the study.
Northern Australia is known for having some of the best preserved sedimentary rocks dating from Earth’s Middle Ages (the mid-Proterozoic period), including the oldest biomarker-bearing rocks on Earth.
“The molecular fossils entrapped in these ancient sediments allow unique insights into early life and ecology,” Nettersheim said.
The researchers found that the molecules had a primordial chemical structure that hinted at the existence of early complex creatures that evolved before LECA and had since gone extinct.
“Without these molecules, we would never have known that the Protosterol Biota existed. Early oceans largely appeared to be a bacterial world, but our new discovery shows that this probably wasn’t the case,” Nettersheim said.
Brocks said the creatures probably thrived from about 1.6 billion years ago up until about 800 million years ago.
The end of this period in Earth’s evolutionary timeline is known as the Tonian Transformation, when more advanced organisms, such as fungi and algae, started to flourish. But exactly when the Protosterol Biota went extinct is unknown.
“The Tonian Transformation is one of the most profound ecological turning points in our planet’s history,” Brocks said.
“Just as the dinosaurs had to go extinct so that our mammal ancestors could become large and abundant, perhaps the Protosterol Biota had to disappear a billion years earlier to make space for modern eukaryotes.”
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