Ancient Greenhouse Gases: Givers and Takers of Life

Once upon a time, there was a planet whose sun was dimmer during the first half of the planet’s existence than during the last half of its geologic history. Yet, temperatures were higher during the first half. Why?! How could this be? It was because of the high levels of the greenhouse gases methane and carbon dioxide in the atmosphere. But then, Cyanobacteria (blue green algae) evolved and thru photosynthesis released oxygen as a byproduct. Eventually, the methane and CO2 levels were lowered until the temperatures decreased to the point that the planet was entirely locked in ice. This lasted for millions and millions of years. Finally enough carbon dioxide was emitted by volcanoes and eventually a balance between oxygen and CO2 was achieved. From this point on, the only extinctions that ever occurred were when flood basalt events caused CO2 levels to spike on this, our planet, Earth.

Snowball Earth (4 minutes)
https://youtu.be/YKuoPBbh58Y

Cyanobacteria 
https://en.m.wikipedia.org/wiki/Cyanobacteria

Snowball Earth
https://en.m.wikipedia.org/wiki/Snowball_Earth

Also:

https://samslair.blogspot.com/2020/12/agw-when-too-much-or-too-little-of-good.html?m=1