A University of Arizona geologist and a Yale University colleague say they can use the algae and fungus that grows on rocks, called lichens, to date prehistoric earthquakes. Prof. William Bull, a geoscience professor emeritus from the University of Arizona, and Prof. mark Brandon of Yale say they can use the method, known as lichenometry, to pinpoint the date of prehistoric earthquakes. They outline their findings in the January issue of the Geological Society of America bulletin.