Ecological complexity is impossible without an oxygenated planet, because oxygen is the difference between extracting 10% and 40% of the energy in food.

But the thing is, you can’t have this if you don’t have an oxygenated planet because it’s all, in the end, it’s about how much energy can you extract from the food you eat? And if you don’t have an oxygenated planet, you can get about 10% out, not much more than that. And if you’ve got an oxygenated planet, you can get about 40% out.