Complex sentence: They are among the first living things to grow on fresh rock exposed after a disaster, such as a landslide, and the long life-span and slow and regular growth rate of some lichens can be used to date the disaster (lichenometry).
Split into simpler sentences: They are among the first living things to grow on fresh rock exposed after an event such as a landslide. The long life-span and slow and regular growth rate of some lichens can be used to date the event (lichenometry).