Dust never lasts in nature. It gets washed away with the rain and blown by the wind. Dust storms come and pass. The dog's coat gets dirty and matted, but dirt is not dust.
Dust, as we know it, is our own invention. It accumulates on our surfaces, a layer of dust,
"Those who could not survive the dust had passed into oblivion years ago, and the dust, weaker now and confronting the strong survivors, only deranged minds and genetic properties.” - Philip K. Dick, Do Android Dream of Electric Sheep