For many years, paleobiologists have been investigating the early eukaryotes, but they constantly face the challenge of identifying ancient organisms. This is due to the fact that a billion years have passed since they lived, so any traces they left are likely degraded and are difficult to analyze accurately.
A group of organisms left biomarker signatures in rocks dated to 1.64 billion years, suggesting that they once dominated the planet. It suggests that they lived during the time when the Earth has low-oxygen environment before organisms such as plants, animals, and fungi emerged.
Finding Clues in Biomarkers
The previously known organisms, which were abundant in aquatic ecosystems around the world, were collectively called protosterol biota. They were discovered by paleobiogeochemists Jochen Brocks and Benjamin Nettersheim from the Australian National University.
Brocks and Nettersheim made the discovery after exploring the water channels around the world, the oldest being from the Barney Creek Formation in Australia. They try to find steroids as biomarker of early eukaryotes that emerged in the planet. It was suggested that almost all eukaryotes have the ability to synthesize steroids like cholesterol as suggested in 1994 by Nobel laureate biochemist Konrad Bloch.
In conducting their investigations, the scientists used combined techniques in order to convert different modern steroids to their fossilized equivalent. For many decades, these fossil molecules have been overlooked because they do not align with a typical molecular search images. Upon identifying their target, Brocks and Nettersheim found out that dozens of other rocks from waterways were rich in similar fossil molecules.
The researchers theorized that, in comparison with bacteria, the organisms of the protosterol biota were larger and more complex. They could also thrive on them at the next level in the food web, hunting and devouring the bacteria.
Another interesting discovery is that the traces left by protosterol biota ceased from appearing in the fossils almost 800 million years ago. This is the point in history when algae and fungi began to emerge, while the first animals to ever exist are thought to live around 700 to 600 million years ago.
The scientists suggests that they could be the earliest predators in the world who feast on microbes that were abundant in the oceans during that era. If this theory is correct, the protosterol biota are likely to the ancestors of all the eukaryotes that have ever lived, such as fungi, plants, animals, and even humans.
This means that the eukaryote biomarkers have been hiding in plain sight for many years. Even after their discovery, scientists still cannot identify the creatures that produce them because the fossils of these creatures remain undiscovered. Although they are recognized as significant contributors in shaping the ecosystems of the Earth, these organisms are not likely to survive today.
Origin and Evolution of Eukaryotes
Eukaryotes are organisms whose cells contain a nucleus with genetic material separated from the cytoplasm. Just like prokaryotic cells, eukaryotic cells have surrounding plasma membranes and contain ribosomes. However, they are much more complex and a variety of other organelles not found in prokaryotes.
Eukaryotic organisms emerged at least 2.7 billion years ago, following the evolution of prokaryotes. Investigations about DNA sequences indicate the difference of modern eukaryotes with archaebacteria and eubacteria. This suggests that there could be a time in the evolution where our common ancestor diverged into three branches of descendants, and this gave rise to the present-day archaebacteria.
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