Because he "coined" the name he robbed the concept of its real value so that now, if it is not done with tyres it is not an earthship. I disagree. Massive structures are thermally stable. The more massive, the more stable. Correct design and orientation of the structure are the factors that determine whether it will be comfortably stable, or uncomfortable. I am very close to a good source of gabion fill, so I am contemplating going that route - if I ever get that far. In my book an earthship is an earthship with or without tyres.