Traces of molecules found in ancient rocks reveal a wild ecosystem of early life that hunted and thrived in the world’s oceans for nearly a billion years.
Biomarker signatures found in rocks that have been dated to be 1.64 billion years old have been left behind by a whole host of previously unknown organisms that have dominated life on Earth, in a world with low oxygen levels, an eon before the emergence of plants, animals and fungi.
These organisms were unlike anything alive today. Their discoverers, led by paleobiogeochemists Jochen Brocks and Benjamin Nettersheim of the Australian National University in Australia, have collectively dubbed it the protosterol biota.
They could be the world’s first predators, feeding on microbes that were abundant in the oceans at the time. and they also appear to be the ancestors of all eukaryotic life on earth. That’s all the plants, animals, and fungi that exist now—including us.
“Molecular remains of the protosterol biota discovered in rocks 1.6 billion years old appear to be the oldest remains of our own lineage – they even predate the last common ancestor of eukaryotes (1.2 billion years ago)” says Nettersheimwho is now at the University of Bremen in Germany.
“These ancient creatures were common in marine ecosystems around the world and likely shaped ecosystems for much of Earth’s history.”
Because eukaryotic life – organisms whose cells contain a nucleus – is so dominant today that scientists believe it must have originated more than a billion years ago.
Paleobiologists have long been searching for these early eukaryotes, but identifying ancient organisms is challenging at best. Since they already lived more than a billion years ago, the traces they may have left are most likely badly damaged and difficult to clean up diagnose for sure.
The discovery was made by analyzing rocks from waterways around the world, the oldest of which were from the Barney Creek Formation in Australia and formed 1.64 billion years ago.
They specifically searched for steroids, a biomarker of early eukaryotes first predicted in 1994 by Nobel Prize-winning biochemist Konrad Bloch, since almost all eukaryotes can synthesize steroids such as cholesterol.
“We used a combination of techniques to first convert various modern steroids into their fossilized equivalents; otherwise we wouldn’t even have known what to look for.” Brock’s explained.
He adds“Scientists had overlooked these molecules for decades because they did not correspond to the typical molecular search images. Once we knew our target, we discovered that dozens of other rocks, taken from waterways around the world that were billions of years old, were leaking from similar fossil molecules.
The discovery shows that these eukaryotic biomarkers have been hiding in the dark all along. However, what the creatures that produced them looked like remains unknown, as no fossils of the creatures themselves have been found.
However, the researchers believe that the organisms of the protosterol biota were larger and more complex than bacteria and thrived on them as the next chain in the food web. “We think they may have been the first predators on Earth to hunt and devour bacteria.” says Brocks.
Interestingly, the tracks left by these creatures stopped appearing in the fossil record about 800 million years ago. From this point on, algae and fungi appear; The first animals They are believed to have formed around 700 or 600 million years ago.
The decline of the protosterol biota and the emergence of other organisms is called the Tonian Transformation and is one of the most profound changes Earth’s ecology has undergone, allowing for the rise of modern eukaryotes.
The discovery of sterols, very similar to those our bodies produce today, in a very different group of organisms allows us to trace our history to a much more distant time than ever before.
“The culmination of this discovery is not only the extension of the current molecular record of eukaryotes,” says the paleobiogeochemist Christian Hallmann of the German Research Center for Geosciences in Germany.
“Given that the last common ancestor of all modern eukaryotes, including us humans, was likely able to produce ‘normal’ modern sterols, there is a high probability that the eukaryotes responsible for these rare signatures, for stem of the family tree.”
The research appears in Nature.
