Formation of Replicating Saponite from a Gel in the Presence of Oxalate: Implications for the Formation of Clay Minerals in Carbonaceous Chondrites and the Origin of Life

Abstract

The potential role of clay minerals in the abiotic origin of life has been the subject of ongoing debate for the past several decades. At issue are the clay minerals found in a class of meteorites known as carbonaceous chondrites. These clay minerals are the product of aqueous alteration of anhydrous mineral phases, such as olivine and orthopyroxene, that are often present in the chondrules. Moreover, there is a strong correlation in the occurrence of clay minerals and the presence of polar organic molecules. It has been shown in laboratory experiments at low temperature and ambient pressure that polar organic molecules, such as the oxalate found in meteorites, can catalyze the crystallization of clay minerals. In this study, we show that oxalate is a robust catalyst in the crystallization of saponite, an Al- and Mg-rich, trioctahedral 2:1 layer silicate, from a silicate gel at 60°C and ambient pressure. High-resolution transmission electron microscopy analysis of the saponite treated with octadecylammonium (n(C)=18) cations revealed the presence of 2:1 layer structures that have variable interlayer charge. The crystallization of these differently charged 2:1 layer silicates most likely occurred independently. The fact that 2:1 layer silicates with variable charge formed in the same gel has implications for our understanding of the origin of life, as these 2:1 clay minerals most likely replicate by a mechanism of template-catalyzed polymerization and transmit the charge distribution from layer to layer. If polar organic molecules like oxalate can catalyze the formation of clay-mineral crystals, which in turn promote clay microenvironments and provide abundant adsorption sites for other organic molecules present in solution, the interaction among these adsorbed molecules could lead to the polymerization of more complex organic molecules like RNA from nucleotides on early Earth.

Pressure‐Induced Water Insertion in Synthetic Clays

“…It can also be expected that materials which exhibit the ability to structural breathing related to hydration/dehydration under variation of external conditions, could be highly suitable as environment for the accumulation of organic matter and thus could be an interesting facet in clay-related theories for the origin of life. [5][6] Graphite oxide and clay minerals demonstrate a lot of similarities in respect to their swelling in water since both are hydrophilic layered materials. Clay materials consist of negatively charged layers and charge neutrality is warranted by interlayer cations.…”

Catalyzed Synthesis of Zinc Clays by Prebiotic Central Metabolites

“…High-resolution TEM (HRTEM) analysis of the cross-section through aggregates of sauconite showed disorganized and random arrangements of individual 2:1 layers. Most smectite-group minerals, including synthetic saponite 15 , consist of packets of short-range, turbostratic stacks of 2:1 silicate layers. Both the structure and chemical composition of sauconite resembles, however, other known smectite-group minerals.

Figure 3TEM images and energy dispersive X-ray spectra (EDS) of air-dried whole mount synthesized sauconite with 1.0 M succinate at pH 0 9.0 after 6 h reflux at 90 °C.

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“…Recent work has proven the crystallization of saponite clays can proceed easily in only 20 h under relatively mild conditions in the presence of urea 11 as a catalyst. Interestingly, nowadays abundant oxalic acid, an endpoint oxidation product for all organic matter exposed to environmental oxidizers before their final conversion into formic acid and CO 2 12–14 , successfully substituted urea in the synthesis of saponite clays 15 . The role of oxalate as a chelating agent for aluminum atoms in the octahedral state has been previously studied 16 .…”

Structural, geochemical, and mineralogical investigation of active hydrothermal fluid discharges at Strýtan hydrothermal chimney, Akureyri Bay, Eyjafjörður region, Iceland

“…Oversaturation was calculated for ocean water as well (SI ~ 4). From this, it is obvious that the precipitation of saponite is inhibited and a catalyst is needed (Schumann et al 2012). It can be speculated that the catalyst is provided by the ocean water and temperature may play a role as well.…”