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A detailed planetwide stratigraphy for Mars has been developed from global mapping based on Viking images and crater counting of geologic units. The original Noachian, Hesperian, and Amazonian Systems are divided into eight series corresponding to stratigraphic referents. Characteristic crater densities and material referents of each series are (1) Lower Noachian [N(16)] (number of craters > 16 km in diameter per 106 km2) > 200] basement material; (2) Middle Noachian [N(16) = 100–200] cratered terrain material; (3) Upper Noachian [N(16) = 25–100; N(5) = 200–400] intercrater plains material; (4) Lower Hesperian [N(5) = 125–200] ridged plains material; (5) Upper Hesperian [N(5) = 67–125; N(2) = 400–750] complex plains material; (6) Lower Amazonian [N(2) = 150–400] smooth plains material in southern Acidalia Planitia; (7) Middle Amazonian [N(2) = 40–150] lava flows in Amazonis Planitia; and (8) Upper Amazonian [N(2) < 40] flood‐plain material in southern Elysium Planitia. Correlations between various crater size‐frequency distributions of highland materials on the moon and Mars suggest that rocks of the Middle Noachian Series are about 3.92–3.85 b.y. old. Stratigraphic ages compiled for units and features of various origins show that volcanism, tectonism, and meteorite bombardment have generally decreased through Mars' geologic history. In recent time, surficial processes have dominated the formation and modification of rock units. The overall stratigraphy of Mars is complex, however, because of temporal and spatial variations in geologic activity.

The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed 100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements.

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A committee of the Mars Exploration Program Analysis Group (MEPAG) has reviewed and updated the description of Special Regions on Mars as places where terrestrial organisms might replicate (per the COSPAR Planetary Protection Policy). This review and update was conducted by an international team (SR-SAG2) drawn from both the biological science and Mars exploration communities, focused on understanding when and where Special Regions could occur. The study applied recently available data about martian environments and about terrestrial organisms, building on a previous analysis of Mars Special Regions (2006) undertaken by a similar team. Since then, a new body of highly relevant information has been generated from the Mars Reconnaissance Orbiter (launched in 2005) and Phoenix (2007) and data from Mars Express and the twin Mars Exploration Rovers (all 2003). Results have also been gleaned from the Mars Science Laboratory (launched in 2011). In addition to Mars data, there is a considerable body of new data regarding the known environmental limits to life on Earth-including the potential for terrestrial microbial life to survive and replicate under martian environmental conditions. The SR-SAG2 analysis has included an examination of new Mars models relevant to natural environmental variation in water activity and temperature; a review and reconsideration of the current parameters used to define Special Regions; and updated maps and descriptions of the martian environments recommended for treatment as "Uncertain" or "Special" as natural features or those potentially formed by the influence of future landed spacecraft. Significant changes in our knowledge of the capabilities of terrestrial organisms and the existence of possibly habitable martian environments have led to a new appreciation of where Mars Special Regions may be identified and protected. The SR-SAG also considered the impact of Special Regions on potential future human missions to Mars, both as locations of potential resources and as places that should not be inadvertently contaminated by human activity.