Let me also remind you about the snowball Earth idea. One epoch of the snowball Earth is thought to have existed between around 800 and 550 million years ago. This idea is derived global glacial evidence in the geologic record.

I remind you that during a snowball Earth episode, the global atmospheric concentration of CO2 is thought to have increased and global atmospheric O2 is thought to have decreased.

This is not so good for respirating eukarotes.

Only after the Earth broke out of the snowball Earth episodes around 570 million years ago could growth and diversification of eukaryotes really take off.

This enormous burst of eukaryotic diversity is called the Cambrian explosion.

http://www.biologiateorica.it/organiccodes/cap7/p186.htm