These were one of the first life-forms to appear on Earth billions of years ago. They are still alive in a few localities around the world such as Shark Bay in Australia. They are formed by blue/green algae and as they grow, sand gets trapped and the algae grows over them. Under water they form into mats. On coastal regions or shallow seas they formed into dome-shaped structures metres across. These algae were one of the plants responsible for the creation of oxygen over millions of years. They first appeared approx 3.5 billion years ago. This scene shows the atmosphere thick with smoke from volcanoes. Tiny traces of oxygen existed then.