Only one substance is necessary for all life. It isn't oxygen. Indeed, to a great many microorganisms, oxygen is highly toxic. These anaerobes, including the bacteria that cause gangrene and many that live around volcanic vents at the bottom of the sea, grow only where oxygen is absent. These are counterintuitive forms of life, and they show that, for many organisms, oxygen is a poison. Is it food that we need to live? Organisms need food to grow, sure, but not to live; many creatures survive for prolonged periods without consuming food. Snakes, spiders, frogs, and toads can go for more than a year without feeding. The European salamander Proteus anguinus can go for 10 years between meals, and even crocodiles and lungfish can both survive for 3 or 4 years without feeding. I once met a solitary Bedouin herdsman named Idris in the deserts of Saudi Arabia, who had never eaten anything in his life, though he consumed copious amounts of camel's milk. So no, eating food isn't vital for survival either.
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