The availability of nucleotides on the early Earth is of great significance for the origin of a self-replicating system capable of undergoing evolution. We hereby report the successful phosphorylation reactions of the nucleoside uridine under heating in the “drying pool” prebiotic model at temperatures ranging from 60–75 °C, and by using pyrophosphate as a phosphorylation agent. Uridine monophosphates (UMP) such as uridine-5′-monophosphate (5′-UMP), 2′-UMP, and 3′-UMP, as well as cyclic 2′-3′-UMP, were identified by 31P-NMR. In addition to the above-mentioned products, a dimer of uridine-phosphate-uridine (U-P-U) was also observed. The reactions were promoted by white quartz sand, Mg2+, and by using urea as a condensation agent. The reactions also proceeded without this mixture; however, the yields increased remarkably with the presence of the above-mentioned materials. The results suggest that a hot/evaporating-drying pool of water containing organics, salts, and reactive phosphorus could be sufficient to form significant phosphate esters.
The detection of ammonium-bearing compounds in meteorites, comets, and in Earth’s geologic record is challenging due to the volatilization of ammonia during heating. Struvite (MgNH4PO4·6H2O) is an ammonium-bearing phosphate mineral considered to be relevant to the origin of organophosphates on the early Earth, and it is possible that this mineral may have formed on the early Earth and in meteorites in favorable environments. However, in contrast to other phosphate minerals such as those within the apatite mineral group, there is little evidence of struvite on the early Earth and no detection of it in meteorites, where such high-N (nitrogen) and low-H2O conditions may be more commonplace. Here, we demonstrate that struvite quickly loses ammonia and transforms into a new suite of minerals; hence, this mineral is ephemeral. This ephemerality is demonstrated by the thermal decomposition reactions of struvite that lead to the mineral newberyite (MgHPO4·3H2O), an acidic phosphate mineral. Both struvite and newberyite transform into magnesium pyrophosphate and magnesium triphosphate, which are the final products of thermal decomposition (T > 200 °C). However, magnesium pyrophosphate itself reacts with calcium-bearing minerals such as calcite or gypsum and transforms into orthophosphate minerals and polyphosphate salts. Such reactions could have occurred in meteorites as well as on the early Earth. The present research helps identify how ephemeralbut prebiotically relevantminerals may be lost from the geologic record, but still could have played a role in the development of life.
Phosphate minerals such as those in the apatite group tend to be the dominant forms of phosphorus in minerals on the Earth’s surface. Phosphate can be reduced to phosphides during high-energy events, such as lightning and impacts. Here we show that, in addition to formation of metal phosphides, a new compound was formed by lightning in a fulgurite from New Port Richey, Florida, USA. A calcium phosphite material, ideally CaHPO3, was found in spherules mainly consisting of iron silicides that formed by lightning-induced fusion of sand around a tree root. This phosphite material bears a phosphorus oxidation state intermediate of that of phosphides and phosphates in a geologic sample and implicates phosphites as being potentially relevant to other high-energy events where phosphorus may partially change its redox state, and material similar to this phosphite may also be the source of phosphite that makes up part of the phosphorus biogeochemical cycle.
Iron silicide minerals (Fe-Si group) are found in terrestrial and solar system samples. These minerals tend to be more common in extraterrestrial rocks such as meteorites, and their existence in terrestrial rocks is limited due to a requirement of extremely reducing conditions to promote their formation. Such extremely reducing conditions can be found in fulgurites, which are glasses formed as cloud-to-ground lightning heats and fuses sand, soil, or rock. The objective of this paper is to review reports of iron silicides in fulgurites, note any similarities between separate fulgurite observations, and to explain the core connection between geological environments wherein these minerals are found. In addition, we also compare iron silicides in fulgurites to those in extraterrestrial samples.
Life is a complex, open chemical system that must be supported with energy inputs. If one fathoms how simple early life must have been, the complexity of modern-day life is staggering by comparison. A minimally complex system that could plausibly provide pyrophosphates for early life could be the oxidation of reduced phosphorus sources such as hypophosphite and phosphite. Like all plausible prebiotic chemistries, this system would have been altered by minerals and rocks in close contact with the evolving solutions. This study addresses the different types of perturbations that minerals might have on this chemical system. This study finds that minerals may inhibit the total production of oxidized phosphorus from reduced phosphorus species, they may facilitate the production of phosphate, or they may facilitate the production of pyrophosphate. This study concludes with the idea that mineral perturbations from the environment increase the chemical complexity of this system.
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