The discovery of geologic time revolutionized scientific thinking and led to the development of the modern Earth sciences. Less appreciated, however, is the fact that geologic time has had far-reaching cultural and societal consequences that go well beyond its founding influence upon the geosciences. This essay summarizes the literature describing the difficulties students encounter in understanding deep time, provides an overview of the historical development and cultural relevance of deep time, and suggests ways to increase students' understanding of the significance of geologic time.