Comment by throw0101a

>> rocks, sediment, dirt pee, or literal poop

> This is basically what dust is. It’s everywhere.

What?

> Dust in homes is composed of about 20–50% dead skin cells.[2] The rest, and in offices and other built environments, is composed of small amounts of plant pollen, human hairs, animal fur, textile fibers, paper fibers, minerals from outdoor soil, burnt meteorite particles, and many other materials which may be found in the local environment.[3]

* https://en.wikipedia.org/wiki/Dust

Further: dust is floating in the air and can be removed with decent (MERV ≥11) air filters in your HVAC system. Stuff on the bottom of your shoe makes contact with your floor and stick around until you wash it (and for much longer in the fibre of carpet or rugs).