life II

 Hello Daddy?

How did life first come into being from a dead piece of organic matter?  With this quest in mind, I went forth and reviewed the relevant material and literature from diverse sources. Although serious scientists have applied their scientific and analytical skills for about 70 years now, the results have proved disappointing. From my cursory review, it seems that numerous research groups throughout the world are on the brink of a significant breakthrough. And then I looked back to work conducted in the late 1990s and several research groups working then stated they were on the cusp of a significant breakthrough........

It is to be remembered that conditions on early Earth c3.5 billion years ago were vastly different to today. The atmosphere of that time contained little or no oxygen. This primitive miasma was dominated by the presence of carbon dioxide, water vapour, methane and other trace gasses. Of course, this primitive atmosphere would be noxious and lethal to present-day organisms. The majority of today's creatures, great and small, rely on oxygen for their respiratory metabolism (aerobic). Oxygen levels in our current atmosphere are around 20% and are maintained by organisms utilising the power of photosynthesis. Oxygen is necessary for aerobic respiration, and clearly, the very first life would have had to rely on other means for energy generation.  

The RNA World 

What follows is a highly truncated and simplistic review of how the RNA world is thought to have formed       

All researchers in the field agree that the first life formed in a watery environment. This environment c3.5 billion years ago would be a soup of organic compounds formed from ubiquitous carbon. There are several energetic events that could have been responsible for the synthesis of organic compounds from inorganic molecules. Lightning strikes and thermal energy from volcanoes would have done the trick. At the time of the 'Great Bombardment', meteorites containing organic compounds would have covered the primaeval Earth. It matters not whether the first life appeared in a warm muddy pool or on the ocean floor next to a volcanic vent, there is a fundamental paradox that must be tackled, the ultimate chicken and the egg question. Chains of nucleic acid molecules (RNA and DNA) are required for self-replication, however, this replication can only occur with the help of proteins consisting of amino acids. Both types of molecules are necessary for the propagation of life. What came first, nucleic acids or proteins? Both are required and act in unison for the process of replication. It is hard to imagine that these two exceedingly rare events could happen spontaneously. Perhaps religious folk are correct after all, and a god(s) is/are required to provide the vital spark. One solution relies on the properties of single-stranded RNA molecules. According to this hypothesis, RNA strands act as a template for their own propagation. This process would have to be facilitated by other RNA strands that have folded upon themselves, an innate property of certain RNA strands. These two separate systems would have to spontaneously engage and cooperate to facilitate the replication of single RNA strands with high regard for fidelity. It is to be imagined that open RNA strands would continue to replicate in a milieu of organic chemicals. Competition for free-floating ribonucleotides would then occur. A form of chemical evolution would ensue and ensure that the fastest replicating molecules would dominate and therefore drive the formation of an efficient cooperating replication system. The problem with such a free-floating system is that the replicating RNA strands would be at the mercy of other molecules within the system that might destroy the growing and replicating RNA molecules. Researchers agree that some form of enclosed protective canopy would have had to develop fairly early on to offer some form of protection. Organic lipids in water will spontaneously form spheres. This is due to the molecules having both hydrophilic and hydrophobic regions. That is, one end of the molecule will attract water molecules while the opposite end repels water. The result is that lipids in a watery medium naturally form 'fatty bubbles'. Somehow, the primitive RNA system (I refrain from calling this life) would have had to enter the protective lipid sphere. From there on, the structure would continue to absorb free-floating ribonucleic acids, and the system would continue to replicate. And then, at a suitable time, a portion of the RNA system would bud off and still remain enclosed within a portion of the original fatty domain. And so on, and so on. This model assumes that chemical evolution would drive these primitive systems to become better at replication and at acquiring substrates. Therefore, along the way, most of these competing 'bubbles' would succumb, and at some fine juncture, there would emerge from this chemical deluge a single system that goes on to be refined by natural selection, finally becoming the 'organism' that goes on to beget all life on Earth. If this is the case, then when did the lipid bag of nutrients actually become life. This is moot, I suspect it is analogous to asking when did the first human arise from our ape-like ancestors. Could we actually define a moment and pronounce with absolute rigour/vigour that a particular individual was fully human? And how would we categorise the status of the parents? This proposed continuum presents us with a problem. Could there be a defining moment in the history of our planet when chemical evolution transformed and became life? There is much to ponder here. Of course, all this is pure conjecture, and there are numerous problems with this model. It would be necessary for all the elements to come together almost simultaneously for all this to be feasible. Each step borders on the impossible. The probability that each step in the process could come about and interact stretches probability to unknown realms and, dare I say it, borders on the miraculous. With all that said, it must have happened somehow. The fact that I'm able to sit here and write these words whilst scratching an itch on my twinkle should be testament enough. 

My attempt at explanation is an extremely truncated affair- how could it be otherwise. Also, my limited exposition is only one scenario of how life could have come about. There are alternatives, although many rely on some form of RNA initiation. These alternatives will have to wait another day.