Professor John Higgins' primary research interest is the evolution of the carbon cycle and the global climate system over Earth history. One focus has been on processes that control the chemical composition of seawater, and how those processes have changed on geologic timescales. Another is how on the chemistry of carbonate sediments is affected by processes that occur post-deposition. These include early diagenetic recrystallization, dolomitization and hydrothermal alteration. The tools Prof. Higgins has employed to study these include numerical models of chemical and isotopic biogeochemical cycles, as well as analysis of traditional stable isotopes of oxygen and carbon, and new isotope systems such as magnesium, calcium, and potassium.