I vividly remember attending the 14th International Meeting on Organic Geochemistry in 1989 in Paris. I witnessed a presentation by John Hayes during which he introduced both a conceptual framework for interpretation of stable carbon isotopic compositions (?13C values) of biologically-derived compounds (biomarkers), as well as a novel analytical approach to measure ?13C values of individual compounds using isotope ratio monitoring-gas chromatography mass spectrometry (irm-GCMS; today, this is typically abbreviated as GC-irMS). The paper stemming from this presentation (Hayes et al., 1990), as well as another from the same year led by Kate Freeman (Freeman et al., 1990), were the first in a series of seminal contributions from John's group at Indiana University that laid the foundation for compound-specific isotope analysis (now often abbreviated as CSIA) to emerge as a brand-new sub-discipline. While the approach has its roots in biogeochemistry, it has been embraced by many other disciplines, including environmental geochemistry, ecology, petroleum geochemistry, forensic science, paleoclimatology and paleoceanography, and astrobiology.
