Knoll, A.H.; Walter, M.R.; Narbonne, G.M.; Christie-blick, N. (2004). "A new period for the geologic time scale"(PDF). Science(Washington). 305 (5684): 621-622. Arkiveret(PDF) fra originalen 29. september 2007.
Knoll, A.H.; Walter, M.R.; Narbonne, G.M.; Christie-blick, N. (2004). "A new period for the geologic time scale"(PDF). Science(Washington). 305 (5684): 621-622. Arkiveret(PDF) fra originalen 29. september 2007.