Phosphorus (P) plays a vital role in the origin of life as a component of amino acids that make up DNA, RNA, proteins, and adenosine triphosphate (ATP). The mineral schreibersite, (Fe,Ni)3P, is considered an essential source of phosphorus for the emergence of life on early Earth because this highly reduced phosphorus-bearing mineral is soluble in water. Meteorites are generally considered the main source that delivered the prebiotic schreibersite to early Earth. However, Benjamin Hess of Yale University and colleagues from the University of Leeds propose an alternative source for the formation of prebiotic schreibersite, suggesting lightning strikes that resulted in chemical reduction of oxidized forms of phosphorus present in terrestrial rocks were as important as delivery of reduced phosphorus by meteorites.
The team studied specimens of fulgurite, a glass produced when lightning strikes rocks, vaporizing and melting them. They identified abundant schreibersite spherules incorporated into the fulgurite matrix using electron dispersive spectroscopy and electron backscatter diffraction analysis. Chemical analysis suggests the formation of the iron (rather than nickel) endmember of phosphorus-bearing schreibersite, which helps distinguish it from extraterrestrial, meteoritic schreibersite. The team estimated that lightning strikes could form up to 10,000 kilograms of reduced phosphorus annually based on the following three factors: 1) the lighting-strike rate as a function of partial pressure of carbon dioxide in early Earth’s atmosphere; 2) the abundance of phosphorus in likely target rocks on early Earth; and 3) the fulgurite-forming rate by cloud-to-ground lightning strikes. Meanwhile, the flux of meteorites is estimated to have provided 100 to 10,000,000 kilograms of reduced phosphorus per year. While meteorite flux generally monotonically decreases with time, the rate of lightning strikes remains relatively constant once the composition of the atmosphere reaches a steady state. Thus, lightning strikes could be a significant and continuous source of reduced phosphorus, which can potentially facilitate the emergence of life indefinitely. This research helps to broaden the conditions in which life can be formed in our solar system or on exoplanets beyond our solar system. If a planet has an atmosphere in which lightning is common, as well as liquid water, that planet can be a more promising place for the existence of extraterrestrial life. READ MORE