These are fossils of stromatolites that can be seen along one of the most popular trails in Glacier Park. CLICK HERE to see more photos taken along the Highline Trail.
Glacier Park is made almost entirely of rocks from the Belt Formation (aka "The Belt Supergroup") - layer upon layer of sandstones, shales, and carbonates from the late Precambrian Era. At that time there were no organisms with bones or shells, so stromatolites like those shown in the photo, are the only fossils that can be found in Glacier Park.
Stromatolites are mound-like, multi-layered colonies of algae (blue-green algae; aka cyanobacteria), and their formation has much to do with the way they change the chemistry of the shallow water they live in. The photosynthetic cyanobacteria remove carbon dioxide from the surrounding water, causing calcium carbonate to precipitate onto their slimy, mat-like colonies. Calcium carbonate, along with grains of sediment (silt, etc.), stick to the bio-film layer that covers the colonies. As the cyanobacteria continue to grow up through the sediment, a new layer forms. This process occurs over and over again, creating layered mounds, columns, or sheets.
Fossils of different species of stromatolites can be found in different areas of the park. Stromatolites that lived in the Precambrian played a major role in increasing the amount of oxygen in the atmosphere of the primeval Earth ("The Great Oxygenation Event"). Living stromatolites can be found today at Shark Bay in western Australia.
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Source: T.N. & E.L. Taylor. 1993. The Biology and Evolution of Fossil Plants. Prentice Hall, New Jersey.