Crater densities are used to determine the relative age of planetary surfaces, where high crater density correlates to an old surface and low crater density equates to a relatively young surface. The smooth, flat, relatively crater-free northern lowlands fit the profile of a young geologic surface, especially in contrast to the ancient heavily cratered southern highlands. The Martian dichotomy between the northern lowlands and the southern highlands is one the largest unknown pieces of Mars’ geological evolution. How did such a global scale event occur? What triggered the dichotomy? When did it happen? These questions guide geologist’s research on the subject. However, recent findings of buried basin depressions imply the underlying lowlands crust is not as young as previously thought, but ancient like the highlands. These findings suggest the dichotomy event happened early in Mars’ geological evolution.

1. Watters et al. (2006), MARSIS radar sounder evidence of buried basins in the northern lowlands of Mars.
2. Watters et al. (2007), Hemispheres Apart: The Crustal Dichotomy on Mars.
3. Watters and McGovern. (2006), Lithosphere Flexure and the Evolution of the Dichotomy Boundary on Mars