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Life on Earth was born at least 3.7 billion years ago, but since then the number of living things has grown exponentially. Surprisingly, some of the earliest life forms on our planet still exist and not just in fossilized form - stromatolites - a life form that has witnessed the entire evolution of our planet can still be discovered in certain areas of the globe. Stromatolites are living fossils, the oldest life forms on Earth. Their existence spans an incredible period - stromatolites have existed for 75% of the period since the formation of the Solar System. They are defined simply as rock structures built by colonies of microscopic organisms that do photosynthesis. These organisms are known as cyanobacteria. As the soil settled in shallow water, bacteria began to grow on it, joining the sedimentary particles and building additional layers until mounds formed. These constructions of microorganisms in the earth are perhaps the essential element in the emergence of more complex life on earth - through their respiration, they produced and developed oxygen on Earth until it came to form 20% of the Earth's atmosphere. Using the Sun as an energy reservoir, stromatolites have transformed the planet into a place capable of supporting all life forms, simple or complex.
