Ion exchange is one type of interacts with the solid to exchange another type of ions. K is called selectivity constant. The superscript indicates the mass number and the subscript indicates atomic number. Thus, the maximum year is 50,000 years. For dissolved C from calcite or dolomite, the C is too old.
R is the isotope ratio.
On the other hand, evaporation of water form soil and water body cause 18 O and 2 H increases.