How did aviation industry come to know about the drastic difference in air pressure in high altitude?
The entire reason why the Comet broke up in midair is because they pressurized the plane in the first place.

It was known for a long time that air at high altitude was thinner. This can be experimentally verified by taking a barometer up to a mountain. This was first done in 1648 (and subject to hot debate regarding the nature of air) more than 250 years before the Wright brothers first flew.