It means that the entire material output of the ancient mining operation — the resource that justified three thousand years of underground expeditions — cannot be found anywhere outside the cave.

The product of all that labor is gone.

Every gram of gypsum that was scraped from cave walls and carried to the surface and used for whatever purpose the ancient communities needed it for was eventually exposed to moisture, rain, humidity, and the normal chemistry of the outdoor environment.

And it dissolved.

Archaeologists who work with organic materials — bone, wood, fiber, leather — are accustomed to the fact that preservation is incomplete and that material evidence decays.

But the decay of organic materials is a matter of degree: under some conditions, much survives; under others, little does.