Reactive phosphorus via simulated lightning discharge: A role for fulgurites in pre-biotic chemistry

Abstract

Apatite is the most common phosphorus-bearing mineral in primary igneous rocks. Despite its early and ubiquitous presence in such rocks at the Earth's surface, its phosphorus exhibits a low reactivity in prebiotic chemosynthesis. This situation may change radically upon the transformation of phosphorus from orthophosphates to pyrophosphates or phosphides which are, in contrast, highly reactive in such scenarios. Pyrophosphates and phosphides are today however, scarce on Earth, generally not being stabilized in rock-forming processes. Noticeable exceptions are lightning-struck rocks (i.e., fulgurites). Here, we present the first evidence of reactive phosphorus (P) in a fulgurite which has been experimentally generated under controlled conditions from natural apatite. Crushed apatite was transformed into a fulgurite through the application of controlled high voltage electrical discharges. We document both the apatite (pre-experiment) and the fulgurite (post-experiment) texture, state, and chemistry. 31P and 19F nuclear magnetic resonance spectroscopy reveals the presence of a reactive P phase (pyrophosphate) in the fulgurite. Our results support the speculation that frequent lightning activity under early Earth conditions may have provided more than 100–10.000 kg/yr of reactive P on early Earth through the generation of reactive P-bearing fulgurites. Their presence may have enabled the chemosynthesis of vital prebiotic components such as RNA and lipids for the emergence of life on Earth.