growthline

Growthline is a term used across biology and geology to describe a visible line that marks a period of growth in a material produced by an organism or by natural processes. Growth lines arise from changes in growth rate, deposition, or environmental conditions and can be annual, daily, or irregular depending on the organism or material.

In living organisms, growth lines appear in bones as lines of arrested growth or other growth marks, in teeth as incremental lines of enamel or dentin, and in hard shells or exoskeletons as successive lines formed with each period of growth. Many mollusks, arthropods, and corals show regular growth lines that can be used to infer age and environmental history. In plants, vascular cambium generates growth rings in wood; the presence and spacing of these rings reflect climate, resource availability, and overall growth rate.

In geology and paleontology, growth lines appear in fossil shells, corals, and certain structures that record periodic deposition. Counting lines can aid age estimation and reconstruct past conditions, while in dendrochronology tree-ring analysis provides climate-related records over long timescales.

Methods for studying growth lines include microscopic examination, often with chemical preparation, and imaging techniques such as microcomputed tomography. Dating and interpretation are typically calibrated with known-age specimens or isotopic data. Limitations include the occasional absence or distortion of lines, diagenetic alteration, and environmental factors that complicate alignment or timing.

See also: growth rings, annulus, lines of arrested growth, dendrochronology.