CHAPTER 9: Radioactive Carbon in Environmental Science

Carbon is a very abundant element in biological and earth materials and it is widely distributed in the atmosphere, biosphere, and hydrosphere, and in soil and rock systems. The isotope ¹⁴C is unstable and decays at a known rate. Plants absorb some of the trace ¹⁴CO₂ during photosynthesis, with this passing through the biosphere through eating relationships; most plants and animals are therefore in approximate equilibrium with atmospheric ¹⁴CO₂. Once the living organism dies, the gradually declining ¹⁴C provides the basis for a chronometer to calculate the time since death. Improvements in the technique have been made through better understanding of the carbon cycle, cosmogenic flux rates, and the dynamics of Earth systems; improvements in measurement technology; calibration of the radiocarbon time scale and quantification of reservoir effects; and a reduction in sample size requirements. Radiocarbon dating techniques have been applied to sediment sequences to provide chronologies for proxy analyses of climate and environmental changes; to understand the spatial and temporal variability of fires and their impact on the ecology of vegetation systems; to date groundwater systems and investigate recharge rates; and to provide an accurate chronology for ancient societies and their activities.