THE SURFACE OF MARS: AN UNUSUAL LABORATORY THAT PRESERVES AND RECORDS UNUSUAL/CATASTROPHIC EVENTS

Catastrophic and unusual events such as impacts, mega-floods, sub-ice volcanism, and superplume eruptions may be remote, rare, or punctuated, but they do happen--a realization triggered, in part, by the recognition of the importance of these processes in extraterrestrial environments. Our understanding of precursors, processes, and possible biological effects is limited, but some mysteries may be unraveled through investigating the surface of Mars, rather than focusing on Earth. Many features formed by large and/or punctuated events are readily apparent on the megaregolithic/volcanic crust of Mars, but are poorly recorded on Earth where gradual processes such as tectonics and erosion remove them. The surface of Mars attests to a prolonged ice-rich history, whereas terrestrial sub-ice eruptions and most ancient mega-floods on Earth form near transitory ice sheets. In addition, relative to Earth, the sizes of many extraordinary geologic features on Mars are enormous. For example, the 300-km-diameter Pre-Cambrian Vredefort structure in South Africa is Earth’s largest known impact structure; on Mars, the diameters of the Hellas, Argyre, and Utopia Planitia impact basins are 1800, 1500, and 3,800 km, respectively. Martian volcanoes and flood lavas dwarf those on Earth. Catastrophic flood channels on Mars extend thousands of kilometers. With a length equal to the entire United States, the Valles Marineris canyon is composed of interconnected troughs that may be huge volcano-tectonic collapse structures. Mounds within the troughs may be sub-ice volcanoes that are an order of magnitude larger than those on Earth. In stark contrast to Mars, our oceans and atmosphere produce uniform processes that dominate the terrestrial rock record. The infrequency of large magnitude events combined with low preservation potential makes identifying their consequences and deposits in the terrestrial rock record difficult. However, the ancient surface of Mars preserves geologic features and deposits that result from these terrestrially extraordinary catastrophic and unusual events. Considering the effects of such processes on Mars may help pinpoint the relative importance of random, catastrophic processes, as compared to gradual uniform processes, in shaping the geomorphic, climatic, and biotic history of Earth.