From an essay in progress:
The atmosphere of our Earth was once dramatically different. If you or I, whisked back to the planet at the time of the earliest living things, were to step out onto the surface unprotected, we would be poisoned and asphyxiated within minutes. If it were daytime, we might briefly see an orange sky.
This alien Earth was the cradle of life. The first organisms came into being there, supported by the energy from the sun, an active geology, and abundant sources of metabolic fuel. The very chemistry of the oxygen-poor atmosphere may have been critical for abiogenesis.
These early organisms were enormously successful replicators. In the simple early ecology, they soon covered the planet with tiny solar-chemical cells. They diligently sought their narrow advantage, reworking the same chemistry of the surface and the atmosphere that had led to their existence, until it was polluted with a corrosive byproduct of their metabolism: oxygen.
The event that followed is sometimes called the Oxygen Holocaust. The chemical changes in the atmosphere, caused by runaway biology, corroded the metabolic sources that had made life possible, oxidized genetic material, and set off a runaway cooling effect that turned the earth into a frozen waste. It is a kind of miracle, perhaps a genuine astronomical improbability we only get to observe due to the anthropic principle, that life survived its first tragedy of the commons.
But the conditions for life, not having been completely extinguished, were sufficiently present, and the evolutionary process persistent enough, that life found new chemical pathways to extract energy from the same corrosive element that had nearly caused its demise. Today, we animals (and our fungi cousins) use oxygen to power our cells. Aerobic respiration allows animals like us to do high energy activities, like foraging and dancing and cooking over a flame.