Isotopes of calcium

⁴⁰Ca comprises about 97% of natural calcium and is mainly created by nucleosynthesis in stars (alpha process). Like ⁴⁰Ar, however, some ⁴⁰Ca is radiogenic, created by radioactive decay of ⁴⁰K. While K–Ar dating has been used extensively in the geological sciences, the prevalence of ⁴⁰Ca in nature initially impeded the proliferation of K-Ca dating in early studies, with only a handful of studies in the 20th century. Modern techniques using increasingly precise Thermal-Ionization (TIMS) and Collsion-Cell Multi-Collector Inductively-coupled plasma mass spectrometry (CC-MC-ICP-MS) techniques, however, have been used for successful K–Ca dating similar in method to Rb-Sr dating, as well as determining K losses from the lower continental crust and for source-tracing calcium contributions from various geologic reservoirs.

Stable isotope variations of calcium (most typically ⁴⁴Ca/⁴⁰Ca or ⁴⁴Ca/⁴²Ca, denoted 'δ⁴⁴Ca' and 'δ^44/42Ca' in delta notation) are also widely used across the natural sciences for a number of applications, ranging from early determination of osteoporosis to quantifying volcanic eruption timescales. Other applications include: quantifying carbon sequestration efficiency in CO₂ injection sites and understanding ocean acidification, exploring both ubiquitous and rare magmatic processes, such as formation of granites and carbonatites, tracing modern and ancient trophic webs including in dinosaurs, assessing weaning practices in ancient humans, and a plethora of other emerging applications.

List of isotopes