Mass Extinction
As oxygen built up in the atmosphere anaerobic bacteria were killed leading to the Earth's first mass extinction.
Accumulation of Oxygen
Cyanobacteria experienced a burst of diversification and growth. Evolution of Multicellularity lead to more efficient/rapid rate of photosynthetic activities.
The oxygen released by cyanobacteria steadily accumulated over vast swathes of the ocean and oxygenated the water
The accumulated oxygen started escaping into the atmosphere, where it reacted with methane. As more oxygen escaped, methane and carbon dioxide were eventually displaced, and oxygen became a major component of the atmosphere.
Multiple Extinction Factors
The long-term accumulation of emitted oxygen(toxic to anaerobes) led to the massive decline or even extinction of many anaerobic microbes.
Beside that, The enormous removal of atmospheric GHG like carbon dioxide and methane. This sharp decline of global temperature steered the Earth into its first ice age.
The earliest ice age that eliminate many life, including cyanobacteria itself.