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A stromatolite is a rock formation that is formed by single-celled organisms called cyanobacteria. The rocks form as a result of sediment and sand grains becoming stuck to the cyanobacteria’s mucus, and then fusing together and creating limestone through calcium carbonate chemical reactions. [1] Stromatolites form in shallow water, where the cyanobacteria thrive due to their photosynthetic nature. The bacteria located closer to the surface of the biofilm produces oxygen through the photosynthetic process, while the bacteria under water and lacking of oxygen, aid in consuming methane and sulfate present in the ocean. [2] The rock formations can be found in Western Australia in Shark Bay, as well as the Bahamas and Canada. Shark Bay is listed as a one of UNESCO’s World heritage sites, and is important to geoscience because the cyanobacteria and stromatolites present today are related to the first species of bacteria that inhabited the planet billions of years ago. [3] Stromatolites began forming during the Archaean Eon, which represents the state of the Earth when it was only four thousand years old. [4] When cyanobacteria first appeared, there was essentially no oxygen in the atmosphere, causing living conditions to be extreme and promoting natural selection. The cyanobacteria were able to survive and thrive by growing along shallow coastlines and gaining energy from the sun. Through the process of photosynthesis, the cyanobacteria released oxygen, which made atmospheric conditions more supportive of life and evolution. As a result of this evolution, came unicellular and multicellular organisms called a eukaryotes, which contain a nucleus and distinct DNA shaped by chromosomes. About five hundred million years ago, eukaryotic cells and the increasing amount of oxygen in the atmosphere changed the biology of the Earth, and allowed many species to grow and thrive in the oceans and later on land. [5]

Stromatolites are able to give a record of environmental conditions on Earth spanning thousands of years, through the layers of sediments that the rock has accumulated. The photosynthetic process of cyanobacteria, the atmosphere, and the tides of the shallow water in which they form, shape the growth of stromatolite rocks. For these reasons scientists believe that the fossils and sediment within the stromatolites are able to give insight into the changes of the Earth’s rotation over time. [6] As well as documenting the geological changes on Earth, stromatolites also keep records of biological evolution. As the cyanobacteria live and die within the stromatolite rocks, they release traces of carbonate and silica. Specific types of carbonate such as C-12, are made from biological sources and if found in sediment and rocks can prove the presence of life. [7] Although stromatolites present on Earth today are good representations of the first stromatolites and cyanobacteria, there are chemical differences that can be found. In modern stromatolites scientists have found small organisms called foraminifera that were not in existence during the Archaean Eon, and suggests that modern stromatolite formation may be different than ancient formations. The stromatolites in Shark Bay Australia for example, contain only five percent cyanobacteria, with the majority of biological makeup consisting of younger species of bacteria. [8] This is common in other stromatolites throughout the world, and urges scientists to study the different types of rocks and the bacteria that form them. Research has uncovered that organisms such as archaea, viruses, and eukaryotes are all found within stromatolite formations.


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