Diatoms are aquatic microscopic algae that construct their cell walls from silica, the same material from which your glasses are made. Diatoms are a good example of how scientific knowledge can change with new discoveries. Only a few years ago, it was thought that the primary factor in the excellent preservation of fossils at Florissant was the volcanic ash. However, more recent evidence suggests that diatoms played a major role. Diatoms may have acted much like "plastic wrap" does when you want to preserve food, or a sandwich bag when you want to keep your lunch fresh.
Diatoms would periodically bloom in the shallow waters of the lake when nutrients were abundant, covering aquatic plants and shorelines with a yellow-brown slime and possibly turning the water the same color. Because volcanic activity provided the silica that diatoms need for growth, it would have stimulated diatom blooms in the lake. As they would bloom, the diatoms would create large mats on the surface of the water. Insects and plants, dead or alive, would fall on the mat and be trapped then covered by more diatoms. Eventually the diatom mat with its incased fossils would sink down to the floor of the lake and be covered with more sediment and more mats from above.
This interpretation is one of the leading hypotheses in the strive to understand how fossils were preserved at Florissant which will ultimately give us a more complete picture of the ancient ecosystem of Florissant. Though this hypotheses is currently our best understanding of ancient Florissant, one day new evidence coupled with more research based on the scientific method may completely change everything.
The diatoms in ancient Lake Florissant were freshwater diatoms, but ocean-dwelling, or marine, diatoms that have been around since the Jurassic Period. Florissant is one of the earliest-known occurrences of freshwater diatoms; however, their high diversity at Florissant suggests that they evolved before the Late Eocene.
