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Life

Phylogenetic tree of life

Phylogenetic Tree Of Life

Life, it’s origins hold an extreme fascination to me. From a chemical standpoint life, as I wrote previously, was inevitable from the moment of the big bang. Quite an interesting concept when you really understand that means man is an inevitable and unavoidable outcome. In the past I have written about life’s possible inorganic origins and how it then underwent a chemical evolution changing it into biological life as we know it today. Today I would like to look at it from a different angle.

A phylogenetic tree of living things, based on...

Another Phylogenetic Tree Of Life

Earth made it’s transition from abiotic to biotic about 3.8 billion years ago. The first life was prokaryotic. Of that there is no question. From a more modern perspective LUCA [Last Universal Common Ancestor], looks to be a hyperthermophile so it is assumed that the first form of DNA based life must have had a similar origin. Besides containing an assumption which often leads to error, it has other more serious problems. Let me say I am not ruling out life being ‘helped’ by hydrothermal vents but DNA based life, RNA based life or protein could not last under high temperatures. Besides that the initial assumption is reasonable but should have been quickly ruled out.

Inside hydrothermal vents free fatty acids of varying lengths can form on mineral substrates from Carbon Monoxide and water. Prior to about 3.8 billion years ago Earth was too hot to form liquid water which means life could not form. Organic molecules could form but they could not aggregate into DNA or RNA based life as the temperature would quickly dissociate them. And these fatty acid chains break off from the substrate and find themselves forming micelles, which are tiny spheres of fatty acids, organized such that the tails of the fatty acid point towards the center of the sphere.  At higher concentrations and  appropriate pH, fatty acids micelles can form vesicles. You now have a vesicle which can serve as a protocell which needs nucleotides to cross through the fatty acid membrane. To quote Jeff Goldblum’s character from Jurassic Park, life always finds a way. He wasn’t speaking of protocells here yet the quote is fitting. Life did find a way and nucleotides were able to cross the barrier most likely due to fatty acid flipping at the molecular level. Basically, the nucleotides piggy backed along for the ride.

There are two other nucleotides besides DNA and RNA that may have been possible near hydrothermal vents. Neither are found in nature yet if they were the first nucleotides, they would have been selected out of existence once DNA/RNA formed. The nucleotides I am referring to are PNA [Peptide Nucleic Acid] and TNA [Threose Nucleic Acid]. The evidence for either is inconclusive. PNA is more commonly thought to be a better candidate for life’s first nucleotide than TNA but I have to disagree. TNA has a backbone of Threose which is a tetrose carbohydrate with the chemical formula of C4H8O4. Formaldehyde [methanal] is CH2O. Bet some of you organic chemists see where this is going but for the rest of you reading let me finish. The dimerization of formaldehyde is CH2O + CH2O = C2H4O2 which is Glycolaldehyde. Glycolaldehyde dimerizes as C2H4O2 + C2H4O2 = C4H8O4 and we have the backbone for TNA. Nice, neat and awesome part of the formose series of reactions.

One thing I would like to mention is the incorrect assumption by many that the idea of a primordial or prebiotic soup was disproven leading to the assumption that chemiosis took place at hydrothermal vents or in geysers. The primordial or prebiotic soup is being misunderstood. Firstly, in order to have a deep sea hydrothermal vent or even a geyser there must be liquid water which is exactly what the primordial or prebiotic soup is. Secondly what mechanism is thought to transport the chemicals of life from those hydrothermal vents to the surface of the Earth? There was unquestionably water that had a concentration of organic and inorganic molecules in it.

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