Thrombolites or Living Rocks

Thrombolites are critically endangered microbial structures built by millions of tiny algae and bacteria whose microorganisms resemble the earliest form of life on Earth. They were the only known form of life from 3.5 billion to 650 million years ago and are among the earth’s most primitive life forms. Meaning clotted structure, thrombolites are large bun shaped Cambrian mounds weathering out of flat lying dolostones. They are not exactly fossils, but they are evidence of biological activity, and these unicellular organisms have left a substantial trace in the fossil record. Their internal structure lacks lamination, and furrows containing mud-cracked material that radiate from the centre and down the sides may be drainage channels. They are thought to have thrived in the tidal and subtidal zone of a warm, very salty sea, with some exposed at low tide and covered at high tide, helping explain the mud cracks. The larger mound may be several communities that amalgamated as they grew. Another large colony lies on the shore across the bay to the south, and more numerous but lower examples stand on a small point with a fish hut built on a collection of mounds. These structures are very rare, and another place where they grow is Hamelin Pool, Shark Bay, Western Australia. The darker colored, more rounded boulder nearby is a glacial erratic brought there during the Pleistocene glaciation.

Newfoundland and Labrador · Canada