In the popular 2003 Pixar film, Finding Nemo, a clownfish father’s only son is captured by human aquarium enthusiasts off the Barrier Reef. The story focuses in part on the desperate search of the father to rescue his son. A similar story can be told of origin of life researchers who are striving to recover the notion that the life-giving molecules known as amino acids can be spontaneously produced from inorganic sources.
Back in 1952, Stanley Miller, with the assistance of Harold Urey, conducted an experiment which tickled our curiosity with their ground breaking apparatus which was designed to recreate an early-earth environment. A chemical mixture (H20, NH3, CH4 and H2) in a reducing atmosphere thought to be representative of that environment was heated and given electric sparks (“lightning”) and amino acids emerged! The fanfare over the significance of this discovery was quickly tempered, though, because it only produced a small number of the 20 amino acids essential for life.
Later adjustments to this mixture were made and amongst the different iterations, they produced over 40 different amino acids. Unfortunately, only ten of those were ones needed in living systems. In addition to the inability to account for these missing amino acids, the significance of this research was further confounded with the realization that the early earth atmosphere contained oxygen. In the presence of oxygen any amino acids that might have been produced would quickly be decomposed.
To solve the problem of the missing amino acids, origin of life researchers along with astrobiologists have turned their attention toward space. Extraterrestrial material discovered on earth has been found to possess some amino acids, but it can’t be certain whether their presence can be attributed to contamination from the earth environment. So, space probes are being sent to asteroids to sample their contents in space. Even if these probes are able to identify the presence of amino acids on asteroids, an extraterrestrial source would not have been able to produce the quantity of amino acids needed to meet the demands for the origin of life.
To solve the oxygen problem, it has been suggested the one place on earth with a reducing conditions sufficient for amino acid production is a volcanic vent. In early 2019, researchers at NASA’s Jet Propulsion Laboratory created a model of a volcanic vent in the laboratory which yielded the amino acid alanine (also produced in the Miller-Urey experiment). One of the troubles with this scenario, however, is that the amino acids produced in this environment would not persist very long. At the temperatures which may be found at volcanic vents (600° F) the half-life of amino acids is only a few minutes.
A further complication with deep-sea production of amino acids is the potential for these amino acids to form proteins. Because of the nature of the peptide bonding reaction, it cannot occur in a watery environment. The amino acids must be located in a place where concentrating and drying of the amino acids can occur which is a long way off from the bottom of the ocean.
One more hurdle for moving from amino acids to living cells is that of selection. Each amino acid comes in two forms which are mirror images of each other – referred to as being left-handed and right-handed. In laboratory production of amino acids, both types of amino acids are produced in equal quantities known as a racemic mixture. In living systems, however, only the left-handed versions of amino acids seem to be useful. Based on the Miller-Urey type experiments there are at least 40 different amino acids that could be generated by chance, and therefore over 80 different amino acids from which to choose. This escalates the astronomical improbabilities of randomly forming the proteins (requiring hundreds of amino acids each) needed in life systems. From all the possibilities, how were these 20 amino acids systematically selected?
In the 67 years since Miller and Urey’s experiment, the gap in our understanding of how amino acids originated and became incorporated into living systems has gotten wider. While Nemo’s father was eventually reunited with his long-lost son, the prospects are dim for origin of life researchers. What should be very telling for us is what we do know about the production of amino acids: it requires a lot of concentrated mental effort to design and create controlled conditions which result in amino acids. One of the essential elements for the existence of amino acids seems to be intelligent agency.
Origins of Life by Fazale Rana and Hugh Ross (NavPress, 2004)
James Tour, professor of chemistry and nano-engineering at Rice University discusses claims regarding origin of life research https://www.youtube.com/watch?v=r4sP1E1Jd_Y&t=941s