  We present a theoretical and analytical curve with reproduce essential
features of the frequency distributions vs. diameter, of the 42,000 crater
contained in the Barlow Mars Catalog. The model is derived using reasonable
simple assumptions that allow us to relate the present craters population with
the craters population at each particular epoch. The model takes into
consideration the reduction of the number of craters as a function of time
caused by their erosion and obliteration, and this provides a simple and
natural explanation for the presence of different slopes in the empirical
log-log plot of number of craters (N) vs. diameter (D).
