[Nateman]

Oxygen levels are the obvious answer as to why you had the Cambrian explosion. Oxygen is why plants are stationary and animals move, because oxygen gives animals the energy to move (and taxes the plants for making it!). Once life is on the move you get an explosion of forms taking advantage of this new found motion. It fits nicely with the Ice Ball Earth finally melting letting all those hunkered down plants burst with activity.

[Moonman62]

Oxygen is why plants are stationary and animals move, because oxygen gives animals the energy to move (and taxes the plants for making it!).

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On that note there are on average 5000 mitochondria in each cardiac cell. If it weren’t for eukaryotes evolving there would be no animals.