Did Earth’s early rise in oxygen help multicellular life evolve?

Researchers find that oxygenation of Earth’s surface is key to the evolution of large, complex multicellular organisms. If cells can access oxygen, they get a big metabolic benefit. However, when oxygen is scarce, it can’t diffuse very far into organisms, so there is an evolutionary incentive for multicellular organisms to be small to ensure most of their cells can still access oxygen.