In the last few posts, i wrote about the basics of submarine hydrothermal vents (SHS), here i will be posting about the simulators that we use in the lab to recreate this environment. This is useful as we can use many kinds of basic chemicals to test how they react when directed to massive heat and pressure similar to SHS. Today’s post will be about the most basic of simulator, we call it the autoclave; I will be also describing some of the experiments done in an autoclave system to date.; which literally a boiling pot.
When the hypothesis that life could have started at SHS was proposed; Miller and Bada was one of the first to come with real experimental simulations. They argued that biomolecules decompose at high temperature and pressure, thus making SHS an unreliable spot for origins. They carried out the experiment at 250°C and 26 Mpa for about 6 hours, and adjusted the pH to neutral of amino acids, leucine, alanine, serine and aspartic acid. The experiment was conducted in an autoclave; a device conventionally used to sterilize equipment and supplies by subjecting them to high pressure and temperature (figure on the left and below, you can’t miss it!!). They showed that aspartic acid and serine decomposed rapidly, and the half life of leucine was about 15-20 min; and alanine appears to be much stable than the rest. Glycine, which was not part of the starting material, was produced during the course of the experiments. From this experiment, They went on to conclude that SHS is not ideal for origin of life, because amino acid being an monomer to proteins will be destroyed at high heat and pressure.
This finding, however received much criticism, some scientists mentioned that the duo did not control the redox conditions in their simulations, and started at a neutral pH; this is very much unlikely in a real situation hence, their results are not very realistic. Kohara and and his buddies showed that if a reducing condition (adding hydrogen) is introduced to an autoclave (similar to a real SHS), amino acid are better conserved up to 300°C. The stability of amino acids was dependent on the fugacity of hydrogen in the system compared to inert conditions shown by Miller and Bada. This is shown in Kohara and co workers’ work, that hydrolyzed samples exhibits higher recovery compared to the non-hydrolyzed ones.
Moving on, in 1992, RJC Hennet and friends managed to show that by using some basic chemicals found in the ocean (KCN with NH4CL and HCHO together with pyrite, pyrrhotite and magnetite to be precise) at 150°C, could form a variety of amino acids in an autoclave. Similarly, David Marshall also showed how amino acids and amines could be formed using aqueous NH4HCO3 solutions were reacted with gaseous C2H2, H2, and O2 at 200-275°C for 0.2-2 hours. These experiments seems to be supporting that bio-molecules especially amino acids (so far), could be formed in such conditions which could have existed on early earth.
Now on the cons of autoclave. Despite being robust and proven useful, the autoclaves severely lacks a cooling device. Conventionally, once the heating vessel is removed from the furnace of an autoclave, a fan is usually placed to cool it down for a few hours. This is not exactly how a real SHS will function, one could easily imagine that the hot fluids emitted by the vents will be rapidly cooled down by the near freezing water of the ocean. This limitation made researchers to come with a more dynamic system, which i will write about in the next post.
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