Sclerochronology is the study of physical and chemical variations in the accretionary hard tissues of organisms, and the temporal context in which they formed. The term comes from the three Greek words scleros – hard, chronos – time and logos – science, and refers to the science of ordering events in time. Sclerochronology focuses primarily upon growth patterns reflecting annual, monthly, fortnightly, tidal, daily, and sub-daily (ultradian) increments of time. The regular time increments are controlled by biological clocks which - in turn - are entrained by environmental and astronomical pacemakers.
Familiar examples include annual bandings in reef coral skeletons or daily growth increments in mollusk shells and fish otoliths. Sclerochronology is analogous to dendrochronology, the study of annual rings in trees, and equally seeks to deduce organismal life history traits as well as to reconstruct records of environmental and climatic change through space and time.