Abstract
Magnetite is an iron oxide mineral component of primitive Earth. It is naturally synthesized in different ways, such as magma cooling as well as olivine decomposition under hydrothermal conditions. It is probable magnetite played a significant role in biogenesis. The seawater used in the current work contained high Mg2+, Ca2+ and SO42− concentrations, unlike the seawater of today that has high Na+ and Cl− concentrations. It is likely that this seawater better resembled the ion composition of the seas of the Earth from 4 billion years ago. Cyanide and thiocyanate were common molecules in prebiotic Earth, and especially in primitive oceans, where they could act on the magnetite mechanism synthesis via Fe2+ interaction. In this research, magnetite samples that were synthesized under prebiotic conditions in the presence of cyanide or thiocyanate, (both with and without artificial seawater), showed that, besides magnetite, goethite and ferrihydrite can be produced through different Fe2+-ion interactions. Cyanide apparently acts as a protective agent for magnetite production; however, thiocyanate and seawater 4.0 Gy ions produced goethite and ferrihydrite at different ratios. These results validate that Fe3+ oxides/hydroxides were possibly present in primitive Earth, even under anoxic conditions or in the absence of UV radiation. In addition, the results show that the composition of water in early oceans should not be neglected in prebiotic chemistry experiments, since this composition directly influences mineral formation.
Highlights
The period close to 4 billion years ago was significant with respect to in the number of different types of minerals, which increased due to the evolution of igneous rocks and the weathering caused by the large amount of water at the time
Any molecule that can accept electrons is part of the magnetite-forming process due to the precipitation of Fe(OH)2 [8]. This statement is extremely curious for prebiotic chemistry because it means that unlikely molecules such as water, nitrogen, and carbon oxides may have acted as oxidant agents that led to the formation of other building blocks such as ammonia, formaldehyde, and lipids [9,10,11,12,13,14]
The showed for the synthesis magnetite, KOH and of 3 are necessary controlthat experiments showedofthat for the synthesis magnetite, KOH and
Summary
The period close to 4 billion years ago was significant with respect to in the number of different types of minerals, which increased due to the evolution of igneous rocks and the weathering caused by the large amount of water at the time. Magnetite is an iron oxide with mixed iron valency that was present in primitive Earth [3,4] This prebiotic iron oxide may have been synthesized by magma cooling, olivine decomposition under hydrothermal conditions, or pH increases in Fe2+ solutions generated through weathering [5,6,7]. In the latter case, thermodynamically instable hydroxide (Fe(OH)2 ) is produced and, even in the total absence of oxygen or other oxidizing agents, Fe(OH) is transformed directly into magnetite. Other molecules must have been important in the magnetite synthesis process under prebiotic conditions
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