It surprised me to discover that most of the raw gypsum material used by Westroc Canada to make drywall comes from the "scrubbers" on the top of the power plant smoke stacks, and the rest comes from re-cycled boards. Yes, cleaning up air pollution produces a very pure gypsum that ends up on our walls.
So why do we call "gypsum board" -- "Drywall"? Because in the old lath and plaster days they put the plaster on the wall in a "wet" state and then smoothed it out. DRYwall was a revolution that speeded up and reduced the cost of housing, giving us smooth walls without the highly skilled labour required to plaster a large surface like a wall or a ceiling.
Yes, the photo is a conveyor belt with a single piece of drywall probably 100 feet long. We did a whole TV segment following the entire process from powder to stacks of drywall sheets ready for shipping to stores.