Stromatolites or also known as stromatoliths are layered mounds, columns, and sheet-like sedimentary rocks. They are formed by the growth of a layer on layer of cyanobacteria and other forms of bacteria.

They are the earliest known fossil evidence of life on Earth. The oldest known stromatolites are supposed to be 3,710 million years old and were discovered in Greenland.

Cyanobacteria is the first known organisms to photosynthesis and produce oxygen. Early cyanobacteria in stromatolites are supposedly responsible for increasing the amount of oxygen in the primaeval Earth.

After a billion years, the effect of this photosynthesis began to make a huge impact on the atmosphere. This process is known as the Great Oxygenation Event. The event killed most of the organisms which could not live in or adapted to oxygen, and led to the formulation of today's environment, that we live in.

Image Source: Wikimedia
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