In this case they are estimating the ages based upon the known ages of the geologic formations surrounding the layers of sand the tracks were found in [0][1].

In this case they are estimating the ages based upon the known ages of the geologic formations surrounding the layers of sand the tracks were found in [0][1]. [0] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237636#sec016 https://journals.plos.org/plosone/article?id=10.1371/journal... [1] https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock/ https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock...