生物地球化学是一门研究影响自然环境组成的化学、物理、地质和生物过程的科学。生物地球化学所研究的自然环境包括生物圈、冰雪圈、水圈、土壤圈、大气层和岩石圈。具体来说，它主要研究化学元素在地球内的循环，比如碳循环和氮循环，同时研究这些元素和生命之间在地球上的相互作用和结合。这门科学侧重于研究由生物活动引起的或影响生物活动的化学循环，尤其侧重碳循环、氮循环、硫循环和磷循环。生物地球化学是一门系统科学并与系统生态学密切相关。

Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the cryosphere, the hydrosphere, the pedosphere, the atmosphere, and the lithosphere). In particular, biogeochemistry is the study of the cycles of chemical elements, such as carbon and nitrogen, and their interactions with and incorporation into living things transported through earth scale biological systems in space through time. The field focuses on chemical cycles which are either driven by or have an impact on biological activity. Particular emphasis is placed on the study of carbon, nitrogen, sulfur, and phosphorus cycles. Biogeochemistry is a systems science closely related to systems ecology.