The ancient sedimentary rock containing mollusc fossils has revealed a world of primitive eukaryotes who dominated aquatic ecologies between 1.6 billion and 800 million years ago.
The findings published on June 7th in NatureThe results of laboratory analyses of rocks from around the world revealed Remains of protosteroids, primitive compounds. Researchers claim that eukaryotes (ancient life forms) were responsible for the production of the majority of molecules involved in creating steroid hormones. These organisms include plants, animals, algae, and fungi.
Like cholesterol, steroids are important components of cell membranes. Steroids don’t degrade easily and their remnants can be detected in sedimentary rocks as molecular fossils.
The last common ancestral ancestor to all eukaryotes lived between 1.2 and 1.8 billions of years ago. Scientists know very little about the ecology, habitats and abundance of these early microorganisms. There have been eukaryotic molluscs and fossils dating back to 800 million year ago. Further back in history, physical fossils and molecular traces of steroids are no longer detectable. The existence of protosteroids had been predicted but it was unclear what they would look like — or if they could even be detected — until the researchers figured out a way to re-create those molecular footprints in the lab.
“This study explains why we don’t see footprints of these guys in the rocks, as researchers were looking for the wrong thing,” says biologist Laura Katz, a biologist at Smith College in Northampton, Mass., who was not involved with the new work. “It fills a void in the fossil records.”
The absence of eukaryote remains before 800,000,000 years ago led scientists into the conclusion that the ecosystem was dominated at that time by bacteria. The eukaryotes of the primordial period may not have been strong enough to leave steroid residues.
Scientists had another explanation. What if an intermediate molecule of the chemical pathway which produces modern steroid was the final product in primitive eukaryotes. The biochemist Konrad Bloch proposed this theory, and he won the Nobel Prize for physiology or medical research in 1964.
Geochemist Jochen Bocks and his colleagues from the Australian National University, Canberra, artificially aged molecules that were made during the first steps of steroid synthesis. These included lanosterol, cycloartenol, and other molecules. That revealed what the compounds’ molecular fossils would look like. These fossils were then found in the tar-like bitumens or oils that had been extracted from ancient rocks around the globe.
The researchers found that the protosteroids were abundant in samples taken from both deep and shallow water environments. The oldest sample dates back 1.6 billions of years and came from Australia’s Barney Creek Formation.
“One of the greatest puzzles of early evolution is, why didn’t our highly capable eukaryotic ancestors come to dominate the world’s ancient waterways? Where were they hiding?” says Benjamin Nettersheim, a geobiologist at University of Bremen in Germany. “We show that the protosteroid-producing microorganisms were hiding in plain sight and were in fact abundant in the world’s ancient oceans and lakes all along.”
Some bacteria have the ability to produce protosteroids, even though they are a different type of molecule called hopanoids. But these bacteria only exist in niche habitats, like methane vents and hydrothermal seeps. Their molecular fingerprints were not found in any sediments older that 800 million years. This led the researchers to conclude eukaryotes predominated ancient ecosystems.
“Konrad Bloch would have been delighted, had he lived, to see this,” says MIT geobiologist Roger Summons, who wasn’t involved in the study. “This paper has elegantly confirmed his prediction that biosynthetic precursors to cholesterol reflect ancient life’s quest for improvement.” (Bloch died in 2000.)
It is possible that the primordial eukaryotes thrived better because of their ability to produce these steroid-precursors, which require less oxygen and more energy. early Earth’s harsh low oxygen conditionsResearchers propose (SN: 10/30/15).
“If true, [this study]This suggests that we might be able examine the evolutionary steps of eukaryotes by looking at [an] unprecedented level of detail,” says evolutionary biologist Yosuke Hoshino of the GFZ German Research Centre for Geosciences in Potsdam, who was not involved in the study. “This is such a great opportunity to understand the evolution of complex life, which biologists have always dreamed of.”
