What important gas did stromatolites release intot he atmosphere?

Stromatolites, which are layered structures formed by the activity of cyanobacteria, played a crucial role in Earth's history by releasing oxygen into the atmosphere through the process of photosynthesis. This significant increase in atmospheric oxygen, known as the Great Oxidation Event, occurred around 2.4 billion years ago and dramatically changed the planet's environment, paving the way for the evolution of aerobic (oxygen-using) life forms.