The present paper has three aims. The first and foremost aim is to introduce into philosophy of mind and related areas (philosophy of language, etc) a discussion of Slow Earth, an analogue to the classic Twin Earth scenario that features a difference from aboriginal Earth that hinges on time instead of the distribution of natural kinds. The second aim is to use Slow Earth to call into question the central lessons often alleged to flow from consideration of Twin Earth, lessons having to do with relations of minds to spatially definable boundaries of bodies such as skin or skull. The third aim is to suggest a puzzle for adherents of cognitive content externalism having to do with the metaphysical requirements on slow-switching, a hypothetical process whereby changes in the relations between subjects and their environments are followed by gradual changes in cognitive contents.