Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Geology

Major Professor

Matthew Pasek, Ph.D.

Committee Member

Jeffery Ryan, Ph.D.

Committee Member

Zachary Atlas, Ph.D.

Committee Member

Aurélie Germa, Ph.D.

Committee Member

Heather Abbott-Lyon, Ph.D.

Keywords

Fulgurite, Struvite, Phosphorus, Prebiotic minerals, Schreibersite

Abstract

Phosphorus is a key element in biogenic molecules and the mineral schreibersite is a major reactive phosphorus source for organic compounds on the prebiotic Earth. In this dissertation, a suite of reactions of phosphorus species, which originate from schreibersite minerals on chondrite meteorites and on the early Earth, have been studied to determine the intermediate geochemical pathways between phosphides and common minerals on meteorites and on the early earth.

I first investigated a unique blue fulgurite that was studied to clarify if this blue color was caused by rich phosphorus content, as has been reported for impact glasses that also have a blue coloration. However, the blue color was shown to originate as a pseudochromatic effect, namely Rayleigh scattering from sub-micron spheres embedded in the matrix. Secondly, a solid-state reaction between schreibersite minerals, olivine and calcium silicate minerals has been analyzed, which reveals new thinking about schreibersite oxidation in meteorites. During schreibersite oxidation, phosphate species were the major final product at high temperature (1000 ̊C). However, phosphite, polyphosphates, hypophosphite, and hypophosphate also occurred when temperatures increased (500 ̊C -800 ̊C). Theoretically, I assume that phosphate species could further transform into pyrophosphate as a major product if reaction temperatures were extremely high. Moreover, the rate of this schreibersite oxidation process can be defined, which may determine the thermal record and metamorphic history of chondrite meteorite parent bodies. Finally, I investigated the thermal degradation products of the mineral struvite (MgNH4PO4×6H2O), under conditions expected in meteorites and on the early Earth. Magnesium pyrophosphate and magnesium triphosphate are the final products for the thermal decomposition of struvite. Moreover, magnesium pyrophosphate transforms into orthophosphate and polyphosphate salts with calcium minerals in meteorites, which demonstrates that struvite may be lost from the geologic record, but could still have been important in the development of life.

The results in this dissertation show that reactive phosphorus species in meteorites and in natural glasses have close ties with prebiotic conditions on the early Earth. Some novel relationships between reduced phosphorus sources and minerals in meteorites and on the early Earth have been demonstrated, which provide assumptions to reveal the origin of phosphorus in life, and to understand the environment of the early Earth.

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