Basalt weathering on Earth and on Mars

by Hausrath, Elisabeth M.

Basalt weathering is an important process on both Earth and Mars, yet basalt weathering rates remain poorly understood. This dissertation uses a combination of laboratory experiments, field work, and modeling to study weathering rates under conditions relevant to early Earth and Mars. Basalt weathering profiles have been characterized in arctic Mars analog Svalbard (Norway). Modeling of basalt weathering in Svalbard is used to groundtruth the reactive transport model CrunchFlow, which is then used to interpret observed alteration on the surface of Mars. Mineral dissolution as a function of time and pH is compared in terrestrial environments, and then extrapolated to the surface of Mars. In compiled terrestrial environments, mineral persistence times are approximately: olivine (~10 ka), glass (~250 ka), pyroxene (~1Ma), and plagioclase (~5Ma). Reconnaissance batch experiments were performed to test the dissolution rates of basalt glass and olivine under conditions specifically designed to be relevant to Mars: low temperature, low pH, high ionic strength and oxic and anoxic atmospheres. The absence of oxygen is observed to increase the dissolution rate of fayalite, and the presence of a CaCl2-NaCl-H2O brine is observed to decrease dissolution rates by approximately one order of magnitude. Leaching by citrate of basalt and granite in long-term column experiments enhances the release rate of elements: La,Y, Ce, Th, Al, P, Ti, Fe, Ni, Pb (basalt and granite), Zr, Sc, and Mn (basalt), and V and Zn (granite). This suggests that depletions or enrichments in these elements may prove useful biosignatures in the rock record from early Earth or Mars. Methanogens, microorganisms which may have been important on early Earth and have been proposed to be present on Mars, were grown with a synthesized silicate Ni-containing glass iii to determine whether they might produce a recognizable Ni signature through the production of cell exudates, cell lysates, siderophores, or biofilms. We determine that the largest effect the methanogens might have on weathering in their environment might be through uptake of CO2. iv