Scientists from the Australian National University (ANU) and the German Research Center for Earth Sciences (GFZ) in Potsdam discovered a community of previously unknown organisms that shaped Earth’s ecosystems in the middle ages of the planet. They were much more complex than bacteria and may have been the first predators on Earth, hunting and devouring bacteria.
The study was conducted in the Northern Territory of Australia, where rock formed about 1.6 billion years ago, in which scientists found fossilized fat molecules. Primary chemical signatures were found inside the molecules, hinting that they had stumbled onto something important.
Almost all eukaryotes biosynthesize steroids, such as cholesterol, which is produced by humans and most other animals. These lipid molecules are an integral part of eukaryotic cell membranes, where they help perform various physiological functions. By looking for fossilized steroids in ancient rocks, we can trace the evolution of increasingly complex life.
The protosteroid-producing biota that produced the discovered “protosteroids” belong to a group of organisms known as eukaryotes, which is a massive umbrella that also includes fungi, plants, single-celled organisms, and animals. However, they were very different from the eukaryotes we know today because they evolved on a planet with very little oxygen.
Biomarker signatures found in fossilized fat molecules showed researchers that these protosteroids may have evolved from the last common ancestor of all modern eukaryotes, including humans.
“The highlight of this discovery is not just an extension of the current molecular record of eukaryotes,” says GFZ’s Christian Hallmann. – “Given that the last common ancestor of all modern eukaryotes was probably capable of producing ‘common’ modern sterols, it is highly likely that the eukaryotes responsible for these rare signatures belonged to the trunk of the phylogenetic tree.”
The study of fossilized fat molecules provides new insights into life on Earth billions of years ago and allows scientists to better understand the evolution of life on the planet.