F.M. Gradstein, F.M, J.G. Ogg, A.G. Smith, & al. (2004): A Geologic Time Scale 2004. Cambridge University Press PDFArkivert 1. november 2013 hos Wayback Machine.
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F.M. Gradstein, F.M, J.G. Ogg, A.G. Smith, & al. (2004): A Geologic Time Scale 2004. Cambridge University Press PDFArkivert 1. november 2013 hos Wayback Machine.