January 18, 2022 11:20 pm

Glass played a key role in a historical experiment that recreated the origin of life

A team of researchers from the Higher Council for Scientific Research (CSIC) and the Tuscia University (Italy) have demonstrated the role played by the glass in a historical experiment that recreated the conditions of the origin of life.

This is the experiment carried out by the American chemist Stanley Miller (1930-2007) in 1952 to simulate the conditions that would have given rise to life on early Earth. The results, published in the journal Scientific Reports, open a new way to study how this process happened.

Miller’s experiment showed that complex organic molecules can be synthesized from inorganic precursors, however, part of the success of his experiment lies in the fact that he used a glass reactor

Miller built a glass apparatus into which he introduced water to simulate the early ocean, and a mixture of gases (methane, ammonia e hydrogen) to emulate the primitive atmosphere. As an energy source he used electric shocks between two electrodes that simulated the rays that must abound in the primordial Earth. Within a few days, Miller detected the presence of amino acids –The building blocks of proteins– and other prebiotic organic compounds.

According to this experiment, complex organic molecules they could be synthesized from inorganic precursors. The results supported the idea that the chemical evolution of the early Earth had led to the natural synthesis of the fundamental chemical pieces of life from inorganic molecules. Furthermore, Miller’s work opened the door to experimental studies on the molecular origins of life.

Crucial role of glass

“Now we have shown that the success of the experiment is largely due to the surface of the glass reactor used by Miller,” says the CSIC researcher Juan Manuel Garcia Ruiz, from the Andalusian Institute of Earth Sciences. “Miller simulated the ocean and the atmosphere of the early Earth, but forgot about the rocks. Its crucial role was hidden in the glass walls of the reactor that it used, ”he adds.

The reactor that Miller built for his experiments and the reactors that have subsequently been used by other research groups are made of glass of borosilicato –A particular type of glass with oxides of silicon (silica) and boron–. “Due to the use of ammonia, the gas mixtures in these experiments gave the water a basic pH. Under these conditions, the glass of the reactor dissolves and the silanol groups of the silica are activated, which supposes an increase of the reactivity from the surface ”, details the expert.

Drawing inspiration from his previous research on the role of silica in the phenomena of mineral self-organization, the researchers wondered what role the borosilicate glass walls of the reactor might have in the molecular diversity of the compounds synthesized in Miller’s experiment.

Much of the organic compounds found in older rocks are probably of abiotic origin

Juan Manuel García Ruiz, CSIC researcher

“We conducted six experiments with three reactors: a glass reactor, another made of teflon (a chemically inert material) and a third made of Teflon in which we add glass chips to the water.

The results unequivocally demonstrate that borosilicate glass plays a key role in Miller’s synthesis, in yields, in the number of products synthesized and in their chemical diversity ”, explains the researcher.

“This finding has important geochemical implications because it shows that a large part of the organic compounds found in the oldest rocks of planets such as Earth or Mars, are probably of origin abiotic”, Emphasizes the expert.

Also, the glass was a catalyst necessary to synthesize many of these abiotic organic molecules that are key to the emergence of life. “Miller would have synthesized very few of the organic molecules relevant to the origin of life if he had not used the glass reactor, including dipeptides, multi-carbon molecules, dicarboxylic acids, polycyclic aromatic hydrocarbons or a complete panel of biological nucleobases,” he says. Garcia Ruiz.

Rocks and reducing atmosphere on early Earth

Ultimately, the synthetic pathway discovered by Miller-Urey based on electrical discharge requires expanding the gas phase synthesis scenario to one that includes mineral surfaces. “We thus open a promising avenue of research, that of exploring the role of mineral evolution and the composition of the early Earth’s atmosphere in the performance and complexity of prebiotic compounds on early Earth,” he adds.

It is possible that the rocks also provide the justification to defend the idea most criticized in Miller’s experiments: the existence of a reducing atmosphere (that is, rich in methane and hydrogen) on early Earth.

The reducing atmosphere was produced by the reaction between the first rocks of the earth’s crust when water condensed on the iron-magnesium silicate crust, which led to the massive formation of hydrogen and methane.

“New ideas on the Hadic land (the era that began with the formation of the Earth, 4,600 million years ago and ended 4,000 million years ago) suggest the concomitance of a reduced atmosphere, electrical storms, rocky surfaces rich in silicates, meteoric bombardment and liquid water “, he points out. the investigator.

The reducing atmosphere was the result of the reaction on a planetary scale between the first rocks of the Earth crust when water condensed on the iron magnesium silicate crust 4.4 billion years ago, leading to the massive formation of hydrogen and methane. “This atmosphere was transitory, but it probably lasted almost a hundred million years until it ended up enriching itself in CO and CO.2”, Concludes García Ruiz.


Criado-Reyes, et al. The role of borosilicate glass in Miller-Urey experiment. Scientific Reports. DOI: 10.1038 / s41598-021-00235-4

García-Ruiz et al. Mineral self-organization on a lifeless planet. Physics of Life Reviews. DOI: 10.1016/j.plrev.2020.01.001

Saladino et al. A Universal Geochemical Scenario for Formamide Condensation and Prebiotic Chemistry. Chemistry Europe… Doi: 10.1002 / chem.201803889

Rights: Creative Commons.


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