  We present a statistical analysis of the distribution of large scale
topographic features on comet 67P/Churyumov-Gerasimenko. We observe that the
cumulative cliff height distribution across the surface follows a power law
with a slope equal to -1.69 +- 0.02. When this distribution is studied
independently for each region, we find a good correlation between the slope of
the power law and the orbital erosion rate of the surface. For instance, the
northern hemisphere topography is dominated by structures on the 100~m scale
while the southern hemisphere topography, illuminated at perihelion, is
dominated by 10~m scale terrain features. Our study suggest that the current
size of a cliff is controlled not only by material cohesion but by the dominant
erosional process in each region. This observation can be generalized to other
comets, where we argue that primitive nuclei are characterized by the presence
of large cliffs with a cumulative height power index equal to or above -1.5,
while older, eroded cometary surfaces have a power index equal to or below
-2.3. In effect, our model shows that a measure of the topography provides a
quantitative assessment of a comet's erosional history, i.e. its evolutionary
age.
