Hilltops surrounded by farmland in southern Wisconsin turn out to be the eroded remnants of an ancient archipelago. An island in the Yellow Sea where Korean tourists flock is the peak of a flooded mountain rising from a drowned continental shelf. On the shores of Hudson Bay, where polar bears patrol the Arctic tundra, a close look unveils what was a tropical coastline encrusted with corals nearly 450 million years ago. Markes E. Johnson invites readers on a journey through deep time to find the traces of ancient islands. He visits a dozen sites around the globe, looking above and below today's waterlines to uncover how landscapes of the past are preserved in the present. Inviting and accessible, this book is a travelogue that takes readers through time as well as space. Islands in Deep Time shares the adventure of exploring striking locations across geologic eras and issues a passionate call for their conservation.