Geological age (log10) mean (Log10 M years)

Mean geological age (logarithm to base 10 millions of years before present) derived from the 1:1 million surface geology of Australia (Raymond 2009) by combining the descriptive geological age fields with the timescales database (Laurie et al. 2008) to assign numerical ages to each map unit. The mean age values represent the average of the age values in four fields (MIN_TOPAGE, MAX_TOPAGE, MIN_BOTAGE, MAX_BOTAGE). Rock voids without data including lakes were filled by neighbourhood statistics.