It may surprise someone that Stromatolites are the most important organisms on earth; Stromatolites were the first organisms to produce oxygen. Before the Stromatolites came along, the atmosphere on the Earth was a poisonous fog which consisted of carbon dioxide, carbon monoxide, sulphur dioxide, chlorine gas, ammonia, methane, hydro dioxide (water), and other vulcanic gases (more here). The oceans were full of dissolved iron. The Stromatolites began emitting oxygen as a by-product from their energy production (photosyntesis). First, the oxygen reacted with the dissolved iron, which fell out as layers of iron oxide (rust) on the sea floor. These layers became iron ore and is where we get all our iron from today; parts of the earlier sea floor is now found on land and iron can be obtained from the iron ore through smelting. Second, when the iron in the sea was more or less depleted, oxygen started to accumulate in the atmosphere and allowed life on land. Oxygen high in the atmosphere formed the ozon layer which protected the Earth’s surface from radiation from the Sun. The Stromatolites had quite an impact, in other words. Incredible as it may seem, forms of Stromatolites are still alive today. The picture below shows colonies of living Stromatolites in Shark’s Bay, Australia.