In 1952, Stanely Miller and Harold Urey placed a quantity of water, methane, ammonia and elemental hydrogen gas into a glass vessel and shot electrical sparks through it. The idea was to try to recreate the conditions of the early Earth, with the substances that were assumed to be present, and then determine what sorts of compounds, if any might have been created by such a process. In the case of this historic experiment, Miller and Urey discovered that amino acids, the literal building blocks of life, were made in this process, as well as a raft of other organic molecules. At first blush, this result looked as though the origin of life on our planet could have had a big head start from its early chemistry.
Fast forward nearly 70 years, and Raffaele Saladino at the University of Tuscia in Italy wanted to go back and check on one aspect of the experiment that might have been overlooked in the excitement over the results: the effect of the reaction vessel. Laboratory glassware is borosilicate glass (Pyrex, essentially), and the usual assumption regarding such glass is that it’s inert; it will have no effect on the substance it contains. (This is certainly the assumption of anyone who cooks using Pyrex: the glass is not going to affect the brownies you bake in it.)
Saladino repeated the Miller-Urey experiment in three different vessels: one made of glass, one made of teflon (which is well and truly chemically inert), and one made of teflon, but with pieces of glass placed within it. When the experiment was repeated, complex organic molecules were found as products in plentitude only in the glass vessel. There were respectable amounts of organic compounds in the teflon container containing glass pieces as well, but not as much as in the glass container. Finally, for the teflon container with no glass present, very few organic molecules were produced. Clearly, the container in the original experiment was playing a crucial role.
We think of glass as being chemically inert, but like any other substance, glass is just another chemical, and it does have chemical properties. The important ones with regard to the Miller-Urey experiment are acid-base properties. The reaction mixture had a significantly higher pH (i. e. more basic or alkaline) than the usual sorts of organic reactions performed in such containers. Under these conditions, the glass would have acted as an acid, catalyzing the reaction. (By the way, Miller and Urey were aware that the glass may have played a role in the reaction, but the mention of that small detail got overshadowed by their more exciting results.)
So, what does this discovery imply about the synthesis of the molecules of life on early Earth? Well, recall that glass is made from silica, essentially silicon dioxide, which is abundant in the Earth’s crust. The necessary catalyst was present to make those amino acids. Future experiments include repeating the process in the presence of meteorites and rocks from other planets, to see if the complex building blocks of life could have been synthesized this way in an environment outside the Earth.
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