1. δ 15 N(‰) = [( 15 N/ 14 N sample ÷ 15 N/ 14 N standard ) – 1] × 1000 where the δ 15 N of the standard represented by atmospheric N 2 is 0‰.
2. Geochronology constrains the age of the Mount McRae Shale to between 2501 ± 8 million years ( 1 ) and 2505 ± 5 million years ( 28 ).
3. ϵ(‰) = 14 κ/ 15 κ – 1) × 1000 where 14 κ and 15 κ are the rate coefficients of a reaction for the 14 N- and 15 N-containing reactants.
4. D. M. Sigman, K. L. Casciotti, in Encyclopedia of Ocean Sciences, J. H. Steele, K. K. Turekian, S. A. Thorpe, Eds. (Academic Press, London, 2001), pp. 1884–1894.
5. M. L. Fogel, L. A. Cifuentes, in Organic Geochemistry, M. H. Engel, S. A. Macko, Eds. (Plenum, New York, 1993), pp. 73–98.