Before revision: Under these conditions, the evolution of the isotopic composition in the residual (reactant) material is described by: where R = ratio of the isotopes (e.g., 18O/16O) in the reactant, Rº = initial ratio, X = the concentration or amount of the more abundant (lighter) isotope (e.g.,16O), and Xº = initial concentration.
After revision: Under these conditions, the evolution of the isotopic composition in the residual (reactant) material is described by: where R = ratio of the isotopes (e.g., 18O/16O) in the reactant, R0 = initial ratio, X = the concentration or amount of the more abundant (lighter) isotope (e.g.,16O), and X0 = initial concentration.