Geological age range (M years)

Range in geological ages (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 range in age values is derived from the maximum and minimum of four fields (MIN_TOPAGE, MAX_TOPAGE, MIN_BOTAGE, MAX_BOTAGE). Rock voids without data including lakes were filled by neighbourhood statistics.