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Even the title is absurd: the atmosphere didn’t become breathable — life evolved to breathe the atmosphere.

• NoahKAndrews 3y ago
  There's an inferred "to us"
  • logdap 3y ago
    [dead]
  • qubex 3y ago
    Precisely — whatever ‘us’ is inferred to be, we’d have to be able to breathe whatever atmosphere we are immersed in. There’s selection bias at work here.