Master of Science (MS)
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Phosphate is an essential nutrient on Earth, used by life for ATP, DNA, RNA, and phospholipid membranes. Therefore, if life is or ever was present on Mars, phosphorus may have played an important role in determining the habitability of an environment. Phosphorus does not have a significant volatile phase; its release from minerals is consequently critical to phosphorus availability and prebiotic chemistry. Phosphate release from Mars-relevant minerals such as merrillite and chlorapatite has been previously found to differ significantly from phosphate release from fluorapatite, the dominant phosphate phase on Earth. However, the environments in which phosphate release would have been most relevant to potential early martian life likely did not contain solely inorganic solutions. Instead, early potentially habitable environments likely contained abundant organic matter delivered by carbonaceous chondrites and interplanetary dust particles.
To determine the effect of Mars-relevant organic compounds on dissolution of Mars- relevant minerals, batch dissolution experiments dissolving merrillite, whitlockite, chlorapatite, and fluorapatite in solutions of one of acetic, succinic, methylsulfonic, mellitic, and oxalic acids were conducted. Minerals were chosen to include the dominant phosphate-bearing minerals in martian meteorites (merrillite and chlorapatite), whitlockite, which is similar to merrillite and potentially relevant to Mars, and fluorapatite, the dominant primary phosphate-bearing mineral on Earth. Organic compounds were chosen based on compounds measured in carbonaceous chondrites and interplanetary dust particles and therefore likely to be present in the martian soils, as well as the proposed breakdown products of refractory organic matter in martian soils.
Results of our dissolution experiments indicate that a range of organic compounds likely to be present in martian soils are capable of enhancing nutrient release from the dominant phosphate minerals present in martian meteorites. Phosphate release from chlorapatite, whitlockite, and merrillite was enhanced by four of the organic acids examined (mellitic, oxalic, succinic, and acetic) – methylsulfonic had no effect to slightly inhibitory effect. The effects of the organic acids could be explained by the denticity of the ligand, the strength of the complex formed with calcium, and the extent of saturation of the solutions. Interestingly, the more quickly dissolving Mars-relevant minerals (merrillite, whitlockite, and chlorapatite) were more strongly affected by the organic compounds used than fluorapatite. With recent detections of organic compounds on Mars, these results suggest that organic matter has played an important role on weathering and nutrient release on that planet.
Bartlett, Courtney Lea, "Phosphate Release: The Effect of Prebiotic Organic Compounds on Dissolution of Merrillite, Whitlockite, Chlorapatite, and Fluorapatite" (2017). UNLV Theses, Dissertations, Professional Papers, and Capstones. 2941.