Generally, the five largest lichen thalli diameters are taken, although several statistical methods have been used. If the growth rate is known, the maximum lichen size will give a minimum age for when this rock was deposited. The growth rate curve, a graph of age of a lichen against the date of the substrate on which it is found has to be constructed for an area.
Generally, the five largest lichen thalli diameters are selected, although various statistical techniques have been employed. If the growth rate is known, the maximum lichen size will provide an approximate age when the rock was deposited. A graph showing the relationship between a lichen's age and the date of its substrate must be created for a given region.