Discovery Of New Sorts Of Microfossils May Answer Age-Old Scientific Question
Scientists get long pondered how and when the evolution of prokaryotes to eukaryotes happened. A collaborative research group from Tohoku University and the College of Tokyo may have offered some answers after discovering new kinds of microfossils dating 1.9 billion years.
Details of their findings were released in the journal Precambrian Research on August 19, 2022.
The Gunflint Formation passes through the northern part of Minnesota into Ontario, along the northwestern shores of Lake Superior. The first microbial microfossils were discovered there in 1954, with Gunflint microfossils now recognized as a “benchmark” in the field of life evolution.
Yet, since the 1970s, little study on the diversity of Gunflint microfossils has been conducted, and no conclusive proof of eukaryotic microfossils has been reported.
Seeking to reassess the microfossils, the study team conducted a geological survey of the Gunflint Formation and collected microfossil-containing rocks. After investigating the microfossils’ three-dimensional shape and dimension distribution, they unearthed 5 kinds of microfossils: colonial, ellipsoidal, intracellular inclusion-bearing (ICI), spinous and tail-bearing types.
“The recently found ones are more functional,” said the leader of the group Kohei Sasaki, a research fellow at Tohoku College. “The ellipsoidal microfossils resemble modern cyanobacteria, which developed to improve their tolerance to harsh environments; whereas chemical analysis revealed that the ICI microfossils were packed with nutrients.”
This offers evidence that the microorganisms evolved to store nutrients that would weather environmental stress.
Meanwhile, the spinous and tail-bearing types demonstrated features advantageous for motility and nutrient transfer among cells, a typical morphological feature of eukaryotes.
“Although the dimension of cells is prokaryote by definition, they had already improved eukaryotic functions,” added Sasaki. This indicates that prokaryotes may have started diversifying their functions and preparing for evolution before the emergence of eukaryotes 1.8– 1.6 billion years ago.
The group speculates that the unique environment at the time helped with the divergent expansion of microbial forms. The collision of land masses accelerated oxidative weathering from the fresh continent to the ocean. This increased the nutrient supplies and raised seawater temperatures, making the marine environment unstable.
“Under such conditions, microorganisms probably diversified their morphology as a survival method, paving the way for eukaryotes to evolve,” continued Sasaki.
Sasaki and his group’s landmark discovery will assist scientists pinpoint the timing and factors that ushered in the evolution of prokaryotes to eukaryotes, offering not only geological significance but also helping the fields of life sciences and evolutionary biology too.
More information:
Kohei Sasaki et al, Evolutionary diversification of paleoproterozoic prokaryotes: New microfossil records in 1.88 Ga Gunflint Formation, Precambrian Research (2022). DOI: 10.1016/j.precamres.2022.106798
Read the original article on PHYS.
