This document discusses stable carbon isotopes and their analysis. It begins by defining isotopes as variants of the same element with different numbers of neutrons. Stable isotopes do not undergo radioactive decay. Stable carbon isotope analysis involves measuring the ratio of carbon-13 to carbon-12 in samples using mass spectrometry to understand environments. Terrestrial environments like soils and freshwaters have distinct carbon isotope ratio ranges that can be used to study carbon cycling processes.