Sedimentary Processes on Earth, Mars, Titan, and Venus

The atmospheres of solid planets exert a fundamental control on their surfaces. Interactions between atmospheric and geologic processes influence the morphology and composition of surfaces, and over the course of geologic time determine the historical evolution of the planet’s surface environments including climate. In the case of Earth, the origin of life likely occurred within surface environments that were tuned to favor prebiotic chemical reactions. Microbial evolution and the advent of oxygenic photosynthesis created Earth’s unique atmospheric fingerprint that would be visible from other solar systems. Earth, Mars, Venus, and Titan are examples of solid planets that have relatively dense atmospheres (Table 1). Yet each planet has shown divergent evolution over the course of geologic history, and their atmospheres are a testimony to this evolution. A second manifestation of this evolution is preserved in each planet’s sedimentary record. Processes that operate at planetary surfaces have the potential to record a history of their evolution in the form of sedimentary rocks. Both Earth and Mars have a well-defined atmosphere, hydrosphere, cryosphere, and lithosphere. Interactions among these elements give rise to the flow of currents of air, liquid water, and ice, that in turn transport sediments from sites of weathering and erosion where they are formed, to sites of deposition where they are stored, to create a stratigraphic record of layered sediments and sedimentary rocks. This gives rise to the “source-tosink” concept by which sedimentary systems on Earth have been characterized (Fig. 1). This unifying concept allows efficient comparison between planets. Our study of Mars has matured to the point where source-to-sink has found remarkable analogous application, and even Titan shows strong evidence for source-to-sink systems, albeit formed under very different conditions than either Earth or Mars. Venus, while recently resurfaced by volcanism and lacking a hydrosphere, also shows evidence for sediment transport in the form of surficial aeolian deposits. This provides clear evidence of the general validity of the approach (Fig. 2). Time and history also are critically important cornerstones of the sedimentary record. Our understanding of the evolution of Earth’s very ancient climate derives from detailed examination of the mineralogic, textural, and geochemical signatures preserved in the sedimentary rock record. Furthermore, Earth’s sedimentary record attests to the formation and evolution of continents, plate tectonics, surface temperature, the composition of the atmosphere and