These 1.9-billion-year-old rocks contain some of the best-preserved microfossils ever found. You can see individual cell walls of the cyanobacteria that first pumped oxygen into Earth's atmosphere, making complex life possible.
Daderot, CC0, via Wikimedia Commons
A Record of Early Life
The Gunflint Chert is not a single location but a part of a larger geological unit called the Gunflint Iron Formation, which stretches across northwestern Ontario and into northern Minnesota. This formation, dated to approximately 1.88 billion years ago, is a banded iron formation—layers of iron-rich minerals alternating with silica-rich chert. These bands are a record of a planet in transition, a direct result of the first large-scale oxygen production by photosynthetic microbes.
The discovery of its microscopic treasures was almost accidental. In 1953, geologist Stanley A. Tyler was surveying the region for iron resources. While taking a day off for fishing, he noticed unusual black chert layers among the more common red jasper and collected some samples. Back in his lab, thin sections of this black chert revealed a collection of microscopic spheres, rods and filaments less than 10 micrometers in size. Tyler collaborated with Harvard paleobotanist Elso S. Barghoorn, and in 1954 they announced their findings, pushing back the accepted date for complex life by more than a billion years. Their landmark 1965 paper created a scientific sensation, effectively launching the field of Precambrian paleontology.
The Planet's First Architects
The microfossils within the Gunflint Chert are a snapshot of a diverse microbial ecosystem that thrived in a shallow sea during the Paleoproterozoic Era. The exceptional preservation is due to the chert itself, a microcrystalline quartz that silicified the organisms, capturing their structures with incredible fidelity. Under a microscope, more than a dozen distinct types of organisms are visible. These include filamentous species like Gunflintia and Animikiea, and spheroidal forms such as Huroniospora. One distinctive organism is the star-shaped Eoastrion, or "dawn star."
These organisms, primarily cyanobacteria, were performing oxygenic photosynthesis on a massive scale. The oxygen they released as a waste product reacted with dissolved iron in the seawater, causing it to precipitate and form the iron-rich layers of the formation. Once the iron in the oceans was largely used up, oxygen began to accumulate in the atmosphere, an event known as the Great Oxidation Event. The Gunflint fossils are some of the most direct evidence of the organisms responsible for this planetary transformation, which allowed oxygen-breathing life to evolve. The individual cells range from just 1 to 16 micrometers in diameter.
💡Fun Facts
The name "gunflint" originates from the rock's use by local First Nations and later by fur traders to create sparks by striking it against steel.
Geologist Stanley A. Tyler discovered the microfossils by chance while on a fishing trip near Schreiber, Ontario.
Some of the star-like microfossils, named *Eoastrion*, are so small that hundreds could fit on the head of a pin.
The discovery of the Gunflint fossils in the 1950s nearly quadrupled the known fossil record of life on Earth at the time.
Accessible year-round at various public locations, subject to weather. Park hours apply where relevant.
Admission
Free at road cuts. Ontario Parks vehicle permit fee required for entry to Kakabeka Falls Provincial Park.
Accessibility
Accessing rock exposures requires walking over uneven, natural terrain. Not wheelchair accessible. Viewing platforms at Kakabeka Falls are generally accessible.
