Earth Air refers to the physical reality of Earth where it is not affected by the energies of the Wash. Earth Air and the Wash are separated by a boundary that is impassable except by way of the exits, which are all but invisible except to those who know how to look for them. The boundary is not physical, it simply does not exist unless entered through an exit.

Inside the Wash, the boundary takes on a different characteristic in that it does become somewhat of a physical presence. It's still invisible, but a person can't pass through it like they can in Earth Air. The energy field which makes the boundary has a dampening effect on living beings, causing them to weaken and ultimately die if they don't get away from it. Generally, animals avoid the boundary, as if they have some perception of it that people do not.