Surprisingly complex trace fossils created by the simplest living things

Stromatolites are mounded structures created by the trapping of sediment by microorganisms. They are trace fossils—evidence of an organism’s behavior. The earliest fossils found on Earth are stromatolites; some found in Australia are about 3.5 billion years old.

The stromatolite in this exhibit was collected by CSC geoscience students from the Eocene-age Green River Formation near Rock Springs, Wyoming. The Green River Formation preserves the deposits of lakes that existed in the Wyoming/Colorado/Utah region for several million years. The presence of stromatolites in some of these lake beds indicates that the water must have been too salty for snails and fish to survive. Extensive bacterial mats could form only in the absence of those animals.

Link: https://en.wikipedia.org/wiki/Stromatolite