Exobiology and Evolutionary Biology

Phosphorus Redox Geochemistry on the Early Earth: Extraterrestrial Influences on the Origin and Evolution of Early Life

PI: Matthew Pasek

Phosphorus (P) is cosmically the limiting nutrient for biologic systems. Understanding the geochemistry of P on the early Earth in turn informs potential pathways for the incorporation of P into the prebiotic compounds that led to the origin of life. Our research has shown that reduced oxidation state P compounds (hereafter reduced P compounds) like phosphite and the meteoritic mineral schreibersite may have comprised a substantial portion of the total phosphorus inventory of the early earth. These compounds are capable of reacting with water, oxidants, and organic compounds to provide potentially prebiotic P compounds. We propose to continue our explorations of reduced P geochemistry to understand the history of P compounds at the surface of the Earth through the first two billion years of Earth’s geologic history, and will extend these studies to conditions on other planets. This objective will be accomplished through a series of synthetic experiments and analyses of natural samples.
The experimental work will involve laboratory simulation of oxidation of reduced P compounds to determine potentially prebiotic products. We shall also characterize the P redox state of ancient rocks and impactites by analysis and modeling methods. Our analyses will employ nuclear magnetic resonance spectroscopy (NMR), electron microprobe point analyses (EMPA), and mass-spectrometry (MS) to determine P redox states and fates.
Results from these experiments will detail possible prebiotic pathways for incorporation of P in the origin of life, including the formation of critical polymers like RNA, and the development of oxidative metabolism. Further our data will constrain on the early geochemistry of this limiting nutrient, by elucidating the extent of changes to P redox state by extraterrestrial impacts on the early Earth. In turn these studies may provide a geochemical means of tracking extraterrestrial flux and possibly atmospheric chemistry, and will aid in understanding planetary geochemistry.

The proposed research is highly relevant to the objectives of NASA and the Astrobiology: Exobiology and Evolutionary Biology Program. Our work is particularly relevant to two of the areas of research emphasis: Origin and Early Evolution of Life, and Implications for Life Elsewhere. This research links the formation of reduced P compounds originating from large, frequent impacts to the origin and development of life on Earth, will attempt to maximize the production of critical P-O-C linkages through experiments, and will seek to place these experiments in the context of early Earth environments. Additionally, by determining the presence of inorganic reduced P compounds in natural samples of Archean rock and in impactites we will identify the role of reduced P compounds on the early Earth. Some of this research will characterize changes to the redox state of P during impacts, which in turn will benefit future searches for life on Mars, Titan, and beyond.