Noun
lichenometry (uncountable)
(archaeology, paleontology, geomorphology) A geomorphic method of geochronologic dating that uses lichen growth to determine the age of exposed rock.
In lichenometry, a lichen is presumed to grow radially at a specific, constant rate: this rate is used to estimate the age of the largest lichen on a rock surface, and thus the length of time the rock has been exposed.