Lichens with known, slow growth rates, like Rhizocarpon geographicum, have been used to estimate the dates of geological events such as the retreat of glaciers. Geologist William Bull of the University of Arizona has been using lichen measurements to establish dates for huge rockslides in the Sierra Nevada and other places that were caused by earthquakes. As adaptations for life in marginal habitats, lichens produce an arsenal of more than 500 unique biochemical compounds that serve to control light exposure, repel herbivores, kill attacking microbes, and discourage competition from plants. Among these are many pigments and antibiotics that have made lichens very useful to people in traditional societies. Laboratory experiments have shown that Xanthoparmelia cumberlandia contains compounds that make it distasteful to slugs.
Slugs are quite fond of some other lichens.