How different would Earth be if anaerobic life were the only life form?

Check your subscription status, update your details and more. How different would Earth be if anaerobic life were the only life form? This question was posed as part of New Scientist’s Last Word series, in which readers give scientific answers to each other’s questions.

Here’s what our readers had to say **How different would Earth be if anaerobic life were the only life form, and could it have become sentient?** Some anaerobic life is obligate anaerobic – it can live only in oxygen-free environments, such as the human gut or deep mud. Other organisms can live without oxygen, but prefer it, or live anaerobically but aren’t harmed by oxygen. The biggest problem is that the anaerobic breakdown of sugar is only partial and yields just 5 per cent of the energy that aerobic breakdown does, so anaerobic organisms are generally not multicellular.

Suppose that photosynthetic bacteria never appeared on Earth. If the planet’s atmosphere contained no oxygen, then oxygen-intolerant species that now thrive on Earth only, for example, in deep mud, could live anywhere, including right on the surface. Receive a weekly dose of discovery in your inbox.

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