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Thrombolites are rounded structures formed in shallow water by the trapping, binding, and cementation of calcium carbonate and other substances by colonies of microorganisms, especially cyanobacteria (blue-green algae). The organisms that make up the thrombolites are considered close relatives to those that lived billions of years ago. Scientists believe they are the earliest form of life on earth, dating back 3500 million years, and the origins of oxygen in the atmosphere. These relics are mostly extinct and exist only as fossils - living examples can still be found growing in just a handful of places in the world, one of which is Lake Clifton. Thrombolites are formed when these organisms die and leave calcium carbonate skeletons behind, forming a base for the next generation to live. This process continues, forming a white skeletal mound.