Details of their findings were published in the journal Precambrian Research on August 19, 2022.

The Gunflint Formation traverses the northern part of Minnesota into Ontario, along the northwestern shores of Lake Superior. The first bacterial 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 research on the diversity of Gunflint microfossils has been conducted, and no conclusive evidence of eukaryotic microfossils has been reported.

Seeking to reassess the microfossils, the research team carried out a geological survey of the Gunflint Formation and collected microfossil-containing rocks. After investigating the microfossils' three-dimensional shape and size distribution, they unearthed five types of microfossils: colonial, ellipsoidal, intracellular inclusion-bearing (ICI), spinous and tail-bearing types.

"The newly found ones are more functional," said the leader of the team Kohei Sasaki, a research fellow at Tohoku University. "The ellipsoidal microfossils resemble modern cyanobacteria, which evolved to improve their tolerance to harsh environments; whereas chemical analysis showed that the ICI microfossils were packed with nutrients."

This provides evidence that the microorganisms evolved to store nutrients that could weather environmental stress.