Stromatolite Drilled Tumble Stone
Stromatolites are one of the oldest fossils known, some dating to over 3.5 billion years old. Stromatolites are actually structures formed by huge colonies of blue green algae (or cyanobacteria). Some scientists consider these bacteria to be the earliest life form on Earth. The cyanobacteria which dominate stromatolites process many of the building blocks of life, including oxygen, carbon, and nitrogen.