Artist’s imagination of two primordial eukaryotic organisms of the ‘Protosterol Biota’ on the ocean floor. Based on molecular fossils, organisms of the Protosterol Biota lived in the oceans about 1.6 to 1.0 billion years ago and are our earliest known ancestors. Credit: Orchestrated in MidJourney by TA 2023.
Key points:
- A new study finds a lost world of ancient organisms in billion-year-old rocks.
- Protosterol Biota lived at least 1 billion years before any animal or plant emerged, and are thought to be the first predators of the Earth
- Scientists overlooked the fossils for decades since they do not conform to typical searches.
The discovery of a “lost world” of ancient organisms that lived in Earth’s waterways over 1.6 billion years ago could change our understanding of early life.
Known as the “Protosterol Biota,” these microscopic creatures are part of a family of organisms called eukaryotes. Modern forms of eukaryotes on Earth today 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 Ancestor (LECA). LECA lived more than 1.2 billion years ago.
To make the discovery, the researchers studied fossil fat molecules found inside a 1.6-billion-year-old rock that had formed at the bottom of the ocean near what is now Australia’s Northern Territory. The molecules possessed 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,” said study author Jochen Brocks of Australian National University. “Scientists had overlooked these molecules for four decades because they do not conform to typical molecular search images. But once we knew what we were looking for, we discovered that dozens of other rocks, taken from billion-year-old waterways across the world, were also oozing with similar fossil molecules.”
The researchers say the Protosterol Biota lived at least 1 billion years before any animal or plant emerged, and are thought to be the first predators of the Earth, hunting and devouring bacteria. They were more complex than bacteria and presumably larger.
“One of the greatest puzzles of early evolution scientists have been trying to answer is: why didn’t our highly capable eukaryotic ancestors come to dominate the world’s ancient waterways? Where were they hiding? Our study flips this theory on its head. We show that the Protosterol Biota were hiding in plain sight and were in fact abundant in the world’s ancient oceans and lakes all along. Scientists just didn’t know how to look for them—until now,” said study author Benjamin Nettersheim.
Exactly when the Protosterol Biota went extinct is unknown, although the research duo suspects it was about 800 million years ago during Earth’s ecological turning point known as the Tonian Transformation.
“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,” said Brooks.