Search Results (4)

A Ga isotope is a new proxy for different geochemical processes such as a weathering process, solution process, etc. Si (Si(OH)₄) is ubiquitous in natural water bodies. However, studies on the Ga isotope effect about a Ga³⁺ aqueous solution reacting with Si (Si(OH)₄) are lacking. In this study, the Ga isotope effect of this process will be studied using a theoretical calculation method based on first principles. The results show that the heavy Ga (⁷¹Ga) isotope enrichment ability of different Ga-Si complex solutions is different. The 1000lnβ (‰) sequence of different Ga-Si complex solutions is (OH)₃GaOSi(OH)₃.(H₂O)₃₀ ≈ (OH)₃(H₂O)₂GaOSi(OH)₃.(H₂O)₃₀ > (OH)₂(H₂O)₃GaOSi(OH)₃.(H₂O)₃₀ > (H₂O)₅GaOSi(OH)₃.(H₂O)₃₀ > (OH)(H₂O)₄GaOSi(OH)₃.(H₂O)₃₀. The results show that there are two different reaction mechanisms when a Ga³⁺ aqueous solution reacts with Si-bearing (Si(OH)₄) water; that is, six-coordination Ga-Si complexes and four-coordination Ga-Si complexes are formed at low pH (acidic) and high pH (alkaline), respectively. Compared with a Ga-Si complex aqueous solution under acidic conditions, Ga-Si aqueous solutions under alkaline conditions preferentially enriched the heavy Ga isotope (⁷¹Ga). The Ga isotope fractionation factors (α) between Ga-Si complex solutions and Ga³⁺-bearing aqueous solutions are all negative, which indicates that light Ga (⁶⁹Ga) isotopes preferentially enter the structure of Ga-Si complexes during the formation of Ga-Si complex solutions. At 50 °C, the Ga isotope fractionation factors (1000lnα) of five systems ((H₂O)₅GaOSi(OH)₃.(H₂O)₃₀ vs. [Ga(H₂O)₆]³⁺_(aq), (OH)(H₂O)₄GaOSi(OH)₃.(H₂O)₃₀ vs. [Ga(H₂O)₆]³⁺_(aq), (OH)₃GaOSi(OH)₃.(H₂O)₃₀ vs. [Ga(OH)₃](aq), (OH)₃(H₂O)₂GaOSi(OH)₃.(H₂O)₃₀ vs. [Ga(OH)₃]_(aq), and (OH)₂(H₂O)₃GaOSi(OH)₃.(H₂O)₃₀ vs. [Ga(OH)₃]_(aq)) involved in this study are −0.12, −0.22, −0.07, −0.09, and −0.16 (‰), respectively. Excitedly, Si can affect the enrichment ability of the heavy Ga isotope (⁷¹Ga) in Ga-bearing complex aqueous solutions. This means that when Si is present in aqueous solutions, the enrichment capacity of the heavy Ga isotope (⁷¹Ga) of aqueous solutions will be effectively reduced. Ga in sediments is mainly derived from soluble Ga in the form of adsorbed (Fe, Mn) oxides/hydroxides, and the Ga isotope composition in sediments is heavier than that in basalt. The formation process of Ga-Si complex aqueous solutions influences the Ga isotope fractionation effect and also contributes to the composition of Ga isotopes in sediments. These key Ga isotope fractionation parameters obtained in this study will provide theoretical support for better explaining the reaction mechanism of Ga³⁺ complexes and Si-bearing (Si(OH)₄) water bodies in solution processes and Ga isotope geochemical cycles. Full article

Since the pioneering experimental work performed by Urey and Miller around 70 years ago, several experimental works have been developed for approaching the question of the origin of life based on very few well-constructed hypotheses. In recent years, attention has been drawn to the so-called alkaline hydrothermal vents model (AHV model) for the emergence of life. Since the first works, perspectives from complexity sciences, bioenergetics and thermodynamics have been incorporated into the model. Consequently, a high number of experimental works from the model using several tools have been developed. In this review, we present the key concepts that provide a background for the AHV model and then analyze the experimental approaches that were motivated by it. Experimental tools based on hydrothermal reactors, microfluidics and chemical gardens were used for simulating the environments of early AHVs on the Hadean Earth (~4.0 Ga). In addition, it is noteworthy that several works used techniques from electrochemistry to investigate phenomena in the vent–ocean interface for early AHVs. Their results provided important parameters and details that are used for the evaluation of the plausibility of the AHV model, and for the enhancement of it. Full article

We review the recent progress in the modeling of plasmas or ionized gases, with compositions compatible with that of primordial atmospheres. The plasma kinetics involves elementary processes by which free electrons ultimately activate weakly reactive molecules, such as carbon dioxide or methane, thereby potentially starting prebiotic reaction chains. These processes include electron–molecule reactions and energy exchanges between molecules. They are basic processes, for example, in the famous Miller-Urey experiment, and become relevant in any prebiotic scenario where the primordial atmosphere is significantly ionized by electrical activity, photoionization or meteor phenomena. The kinetics of plasma displays remarkable complexity due to the non-equilibrium features of the energy distributions involved. In particular, we argue that two concepts developed by the plasma modeling community, the electron velocity distribution function and the vibrational distribution function, may unlock much new information and provide insight into prebiotic processes initiated by electron–molecule collisions. Full article

A prevailing strategy in origins of life studies is to explore how chemistry constrained by hypothetical prebiotic conditions could have led to molecules and system level processes proposed to be important for life’s beginnings. This strategy has yielded model prebiotic reaction networks that elucidate pathways by which relevant compounds can be generated, in some cases, autocatalytically. These prebiotic reaction networks provide a rich platform for further understanding and development of emergent “life-like” behaviours. In this review, recent advances in experimental and analytical procedures associated with classical prebiotic reaction networks, like formose and Miller-Urey, as well as more recent ones are highlighted. Instead of polymeric networks, i.e., those based on nucleic acids or peptides, the focus is on small molecules. The future of prebiotic chemistry lies in better understanding the genuine complexity that can result from reaction networks and the construction of a centralised database of reactions useful for predicting potential network evolution is emphasised. Full article