1.5 The Quaternary: Stratigraphic Framework and Terminology. 1.4 Atomic Structure, Radioactivity and Radiometric Dating. A problem in dating lichens is the fact that several thalli can fuse together, making several minor lichens appears as a larger one of older age.
Measuring the diameter of the largest lichen of a species on a rock surface can therefore be used to determine the length of time the rock has been exposed.With the exception of the radiocarbon method, most of these techniques are actually based on measuring an increase in the abundance of a radiogenic isotope, which is the decay-product of the radioactive parent isotope. They are produced by cosmic rays interacting with Earth materials.The data show when a surface, such as an alluvial fan, was created.A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods.More slowly decaying isotopes are useful for longer periods of time, but less accurate in absolute years.