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When I invent a time machine, what is the earliest period in Earth’s history in which I could comfortably survive?
Reymond Aguinaldo
Ilagan, The Philippines
The answer depends on what you mean by “comfortably survive”.
If you mean breathing the air, drinking the water and avoiding extreme temperatures, then you might be able to go back as far as the Ediacaran Period, roughly 640-540 million years ago (mya), when oxygen levels were closer to our own and there was abundant simple, multicellular life.
However, if you mean finding food and avoiding predators, then you might have a hard time in…
