Close-up of a stromatolite found at Shark Bay, Western Australia. Microscopic examination shows them to be composed of numerous cyanobacteria (formerly blue-green algae), which have been preserved due to their ability to secrete calcium carbonate and form large stony cushion-like masses. These masses are among the oldest organic remains to have been found, ranging from 2000 to 3000 million years old. In costal waters such as Shark Bay stromatolite formation continues today.