Aqueous Corrosion of Phosphide Minerals from Iron Meteorites: A Highly Reactive Source of Prebiotic Phosphorus on the Surface of the Early Earth

Abstract

We present the results of an experimental study of aqueous corrosion of Fe-phosphide under conditions relevant to the early Earth. The results strongly suggest that iron meteorites were an important source of reactive phosphorus (P), a requirement for the formation of P-based life. We further demonstrate that iron meteorites were an abundant source of phosphide minerals early in Earth history. Phosphide corrosion was studied in five different solutions: deionized water, deionized water buffered with sodium bicarbonate, deionized water with dissolved magnesium and calcium chlorides, deionized water containing ethanol and acetic acid, and deionized water containing the chlorides, ethanol, and acetic acid. Experiments were performed in the presence of both air and pure Ar gas to evaluate the effect of atmospheric chemistry. Phosphide corrosion in deionized water results in a metastable mixture of mixed-valence, P-bearing ions including pyrophosphate and triphosphate, key components for metabolism in modern life. In a pH-buffered solution of NaHCO(3), the condensed and reduced species diphosphonate is an abundant corrosion product. Corrosion in ethanol- and acetic acid-containing solutions yields additional P-bearing organic molecules, including acetyl phosphonate and a cyclic triphosphorus molecule. Phosphonate is a major corrosion product of all experiments and is the only P-bearing molecule that persists in solutions with high concentrations of magnesium and calcium chlorides, which suggests that phosphonate may have been a primitive oceanic source of P. The stability and reactivity of phosphonate and hypophosphite in solution were investigated to elucidate reaction mechanisms and the role of mineral catalysts on P-solution chemistry. Phosphonate oxidation is rapid in the presence of Fe metal but negligible in the presence of magnetite and in the control sample. The rate of hypophosphite oxidation is independent of reaction substrate.

Prebiotic chemistry: a new modus operandi

“…The most plausible prebiotic source of phosphate is from anoxic corrosion of schreibersite [22,23], a mineral found in iron-nickel meteorites. By a series of disproportionation reactions, this iron-nickel phosphide ((Fe,Ni) 3 P) produces ferrous and nickel phosphates as well as more reduced phosphorus-containing species.…”

Rethinking early Earth phosphorus geochemistry

“…Schreibersite oxidizes in water to completion on relatively short geologic timescales (1-10 4 years), especially if distributed as fine-grained particles, and forms several P species in aqueous solution (33,34 , with P 6ϩ , form. Thus, at room temperature and with simple aqueous reagents, schreibersite can form P compounds with a multitude of oxidation states.…”

“…Thus, at room temperature and with simple aqueous reagents, schreibersite can form P compounds with a multitude of oxidation states. The primary product of schreibersite oxidation by water is phosphite, HPO 3 2Ϫ , with Ͼ50% of the total aqueous P in this form (33,34). A majority of these P compounds likely originate through free-radical combination reactions (35).…”

The First Detections of the Key Prebiotic Molecule Po in Star-Forming Regions

“…However, a key ingredient still evades detection: phosphorus, P. This element is essential for life (Maciá et al 1997), because it plays a central role in the formation of P-bearing macromolecules such as phospholipids, which are the structural components of all cellular membranes. Moreover, living cells on Earth use P-bearing compounds, phosphates, to transport energy in the form of adenosine triphosphate (see, e.g., Pasek & Lauretta 2005). Particularly important to basic biochemistry is the P −O bond, which is fundamental for many relevant biological molecules such as phosphate esters, which are essential for the formation of the backbone of the genetic macromolecule deoxyribonucleic acid.…”