Helmets in space?

Question

how did scientists find out that we needed helmets to breath in space

Answer 1

They used reasoning.

One: We need oxygen to breath.

Two: Any oxygen in space is scattered, so we can not reach enough of it.

Three: We need to bring our own oxygen.

Four: The only way to do so is to have a mini-environment in which there is oxygen.

Five: The best mini-environment would be a helmet.

Answer 2

i think this was figured when the first pilots flew higher and higher and noticed that the air getting thinner and thinner.
maybe this was already figured while trying to climb high mountains.