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Stromatolites in the Ottawa River. Photo: Mike Beauregard / Flickr.

613 Geotours: What the heck is a stromatolite?

By Bruce Burwell on July 6, 2020

We’ve done geotours on either side of the Ottawa River in the past two weeks. This week we’re doing one that’s actually in the river.

Let’s start with a test of your knowledge on this week’s topic: What exactly are stromatolites?

a) An icicle-shaped formation caused by a gradual mineral deposition that hangs down from a cave’s roof
b) The same thing but the one that grows up from a cave’s floor
c) An a capella singing group from Toronto that was popular in the 1980s
d) Remains of algae from hundreds of millions of years ago

The correct answer is d. How did you do? Congratulations! This week we’re going to discover a picturesque location where you can easily see these ancient fossils.

Well actually, they are not fossils at all, since they are not directly showing the structure of a once-living creature. Stromatolites are layered deposits in limestone that are caused by blue-green algae that lived hundreds of millions of years ago. Back then, stromatolites were extremely common, since the algae that created them were the major form of life on earth. In fact, they pretty much ruled the planet for over two billion years. It’s thought that they were critical to the development of most life forms that came afterwards, since the algae created the oxygen that we breathe.

Ottawa’s stromatolites. Photo: Quentin Gall / Flickr.

Stromatolites are only found in a few spots in Canada. We’re lucky to have some clearly visible ones in the region at the base of the Champlain Bridge, on the Quebec side of the river. They are the most easily accessible ones in Canada.

There are a couple of ways to get to the location of the stromatolites. The easiest would be to park in the tiny lot just west of the Champlain Bridge off Boulevard de Lucerne. It’s only about 100 meters to the stromatolites from there. A better way would be to bike there, since it’s right off the bike path.

Either way you choose to get there, you will see a path down to the river from a point only about 50 meters from the bridge. Head down and have a walk around. It’s OK to walk on top of them—they’ve survived half a billion years, so they’re tough.

See? You can walk all over ancient history. Photo: Joanne Anka / Flickr.

In the exposed flat rock, you will see large circular structures that are up to a half-meter in diameter. If you came across these rocks accidentally, you might think you were looking at a fossilized creature of about that size, not a single-celled organism that predated complex plants and animals. And that is really why this is an exciting location. You are looking at direct evidence of life from over 500 million years ago. Dinosaurs were running around 65 million years ago, and humans evolved in Africa only two million years ago. While there is some evidence of earlier life on Earth, it’s definitely not as accessible—or as beautiful to look at—as the Ottawa River stromatolites.

The stromatolites at the Champlain bridge are visible now, but in the spring they may be underwater. A sure way to find out whether they are visible is to look at this page and check whether the height at Gatineau is less than 41.7 meters. If it’s higher than that, they will be under too much water. If it’s close to that, then bring your boots.