Scientist think colonies of Cyanobacteria called stromatolites were responsible for the introduction of oxygen into earths atmosphere is true.
Explanation:
In primeval earth’s atmosphere, stromatolites (colonies of Cyanobacteria) are believed to have increased the level of oxygen by their photosynthesis process.
These are the first known organisms that started photosynthesis process and produced the oxygen to the earth’s atmosphere.
There is a theory that, these organisms produced oxygen in the environment and the organism disappeared that couldn’t live in the atmosphere with the oxygen.
Scientists gave this a name called as “great oxygenation event”.
