Although Mars has been the focus of planetary exploration over the past three decades, most effort has centered on evaluating the distribution and history of near-surface liquid water as a marker for potential habitability – for ancient and extant life and for future exploration – and so much of the data are more relevant to questions of surficial processes over geological time. These findings are important, but not central to our investigation. Accordingly, we have resisted the temptation of focusing too much attention on these results, as impressive as they are. Instead, we consider them where they address major questions of crustal evolution that are the subject of this enquiry. There are several up-to-date reviews of the recent findings from the Mars exploration programs for those so interested.

Martian crustal evolution represents a near-perfect intermediary between the simple and mostly ancient crustal histories of Mercury and the Moon, where primary crusts dominate, and the extended evolution of Earth. On Earth any primary crust that may have existed is long since lost from the geological record and both secondary and tertiary crusts formed, but at very different rates, over some four billion years.

Sampling martian crust

Mars presents unique challenges in obtaining representative sampling of the crust.