A view of a unique geologic formation known as a banded iron formation near Wawa, Ontario.  The line swirls of this formation are seen directly across the highway towards the top.  This area of glacially polished bedrock is comprised entirely of banded iron formation, dating it from 1.85 to 3 billion years of age.  While not actual organisms, they are considered as fossils in the geologic timetable.  Very magnetic in nature, a combination of hematite & magnetite mixed w/ chert & shale, these formations formed in sea water from oxygen released by photosynthetic cyanobacteria.  The oxygen combined w/ the dissolved iron & precipitated into a thin layer on the ocean floor, to which overtime layers resulted in the banded layering.  At some point the oceans became overly oxygenated (to which oxygen was a major poison to early life forms), that it became known as the Great Oxygenation Event.  The resulting effect was a widespread extinction of early bacterial life forms as oxygen began to fill the atmosphere.  While not entirely clear, when these oxygen levels stabilized, the banded iron ceased their formation around 1.85 billion years ago (a smaller documented event was evaluated b/w 800 to 600 million years ago).

The Canadian Shield contains some of the oldest rocks & geology on earth.  Banded iron is not uncommon w/in the area & today these deposits have been a source of iron, yielding to much mining done particularly in northern Minnesota (which of course leads to a great commerce of ship transportation from Lake Superior down to the Rust Belt of Ohio & Pennsylvania).  Other such mining occur in Australia, where The Outback contains some of the oldest documented rocks known.

More info here: https://en.wikipedia.org/wiki/Banded_iron_formation