Nature of The RealmThe Physical realms are considered both material and perishable. Material things do not last forever, and they are frequently subject to compositing and/or mutation into new forms.
Rarified Elements vs. Composite Physical MaterialFurthermore, even these base realms function at a higher level than what we generally consider physical reality. Rainwater is not the same as the element of Water, and a match flame is not pure elemental Fire. Everything that we can physically interact with is a composite of elements, comprised of elemental combinations.
Hence, even the realm of earth, the basest of the Terrestrial realms, is still more pure, more rarefied than the physical soil beneath our feet or the flesh from which we are made.