Microscopic creature discovery could be ‘oldest remains’ of human lineage, study says.
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 the 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 cellular structure that includes mitochondria, the “powerhouse” of the cell, and a nucleus, its “control and information center.”
Modern forms of eukaryotes include fungi, plants, animals, and single-celled organisms such as amoebae.
Humans and all other creatures with nuclei can trace their lineage back to the last eukaryotic common ancestor (LECA), which lived more than 1.2 billion years ago.
The new findings “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 around the world and likely shaped ecosystems for much of Earth’s history.”
The discovery of Protosterol Biota is the result of 10 years of work by ANU researchers and was published in Nature on Thursday.
ANU’s Jochen Brox, who made the discovery with Nettersheim, said the Protosterol Biota are more complex than bacteria and possibly larger, although it is not known what they look like.
“We believe they may have been the first predators on Earth, hunting and ingesting bacteria,” the professor said in a statement.
Researchers from Australia, France, Germany and the United States examined fossil fatty molecules found in rock that formed on the ocean floor near what is now Australia’s Northern Territory for the study.
Northern Australia is known for some of the best-preserved sedimentary rocks dating from the Middle Ages on Earth (mid-Proterozoic), including the oldest biomarker-bearing rocks on Earth.
“Molecular fossils captured in these ancient sediments allow unique insights into early life and ecology,” Nettersheim said.
The researchers found that the molecules have a primary chemical structure that hints at the existence of early complex creatures that evolved before LECA and have since become extinct.
“Without these molecules, we would never have known that the Protosterol Biota existed. The early oceans largely looked like a bacterial world, but our new finding shows that this probably wasn’t the case,” Nettersheim said.
Brox said the creatures probably flourished from about 1.6 billion years ago to 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, began to flourish. But exactly when the Protosterol Biota became extinct is unknown.
“The tonal transformation is one of the most profound ecological turning points in the history of our planet,” said Brocks.
“Just as the dinosaurs had to go extinct for our mammalian ancestors to become large and abundant, perhaps the Protosterol Biota had to go extinct a billion years earlier to make way for modern eukaryotes.”