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Comins, Niel F.; William J. Kaufmann III (2005). Discovering the Universe, 7th edition, New York, NY: Susan Finnemore Brennan. 0-7167-7584-0.

Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's)

Van Andel, Tjeerd H., New Views on an Old Planet: a History of Global Change (2nd edition, 1994)