Katie Paterson's Fossil Necklace is a gorgeous piece whose each bead is a chronologically ordered artifact from a significant moment in our planetary history, signposting events like the cretaceous, the rise of hominids, and more. (this PDF has detailed, piece-by-piece labels)
'Fossil Necklace is a string of worlds, with each bead modestly representing a major event in the evolution of life through a vast expanse of geological time. From the mono-cellular origins of life on earth to the shifting of the continents, the extinction of the Cretaceous period triggered by a falling meteorite, to the first flowering of flowers, it charts the development of our species and affirms our intimate connection to the evolution of those alongside us. Each fossil has been individually selected from all corners of the globe, and then carved into spherical beads in a secondary process of excavation.' Guy Haywood, Kettle's Yard.
(via Making Light)