Answer: Earth's crust would crumble since Oxygen constitutes 45% of the Earth’s crust. also, everyone's inner ear will explode- We would lose about 21% of the air pressure in an instant, which would be similar to jumping from sea level to nearly 2000m almost instantly. This would prevent the eardrums from becoming acclimated to the changes in pressures. We would experience something called barotrauma (refers to injury sustained from failure to equalize the pressure of an air-containing space with that of the surrounding environment).
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