This book results from a workshop at the International Space Science Institute (ISSI) in Bern, Switzerland, where geochemists, geophysicists, and photogeologists have combined their expertise to constrain the timescales and geological processes in the evolution of Mars. In order to achieve this goal, the ages of cratered lunar surfaces, which are dated precisely by the radiometric ages of returned samples, have been taken as a reference for the inner solar system chronology. The derived ages of cratered geological units on Mars indicate ongoing geological activity from about 4.5 Gyr ago till modern geologic time. Ancient surfaces involve primordial crustal material with strong magnetization that has remained from Mars’ core formation within the first 20 Myr of the solar system, whereas other surfaces were created during major geological processing at about 3-4.5 Gyr ago, probably associated with a denser atmosphere and more fluvial environment, and also to exposures of volcanism. The youngest surfaces indicate volcanism, weathering, gullying, exhumation, and modest water release all operating within the last few 100~Myr, with the youngest detected flows at less than 10 Myr ago. Neither Earth nor Moon offers such a complete geological record. This picture is consistent with radiometric age data of Martian meteorites which indicate that Mars has not only ancient crustal material, as represented in the ALH84001 meteorite, but at least some geologically young igneous rocks with ages of a few 100 Myr. Remote sensing of the Martian surface identifies two broad groups of igneous rock units, basaltic and andesitic, as is confirmed by in-situ chemical analyses at the Pathfinder landing site. Based on these results, the book contains an update on the overall stratigraphic system and geologic processes of the Martian surface, and a recent review on the newest models of the Martian interior structure and on the knowledge about the history of the Martian atmosphere and hydrosphere.
