Detailed Chemical Model Gives Insight into the Origin of Life
There have been many narratives that speculate as to what happened four billion years ago to begin all life on earth. The “primordial soup” theory is one that most of us will be familiar with. The theory was first noted by Russian biochemist in 1924 and is summarised as follows:
- Early Earth had a chemically reducing atmosphere.
- This atmosphere, exposed to energy in various forms, produced simple organic compounds (“monomers”).
- These compounds accumulated in a “soup”, which may have been concentrated at various locations (shorelines, oceanic vents etc.).
- By further transformation, more complex organic polymers – and ultimately life – developed in the soup.
However, this isn’t the only theory around and doubts lead to other alternative possibilities being outlined, one of which being the “mutually catalytic network”. This idea states that groups of molecules can form autocatalytic sets. These are self-sustaining chemical factories, in which the product of one reaction is the feedstock or catalyst for another. The result is a virtuous, self-contained cycle of chemical creation.
However, detailed chemical models needed to be generated to help support such a narrative before we can even begin to speculate what happened to cause the emergence of life on earth.
Prof. Doron Lancet and colleagues at the Weizmann Institute of Science, Dept. of Molecular Genetics reported such a model. First, it was necessary to identify the appropriate type of molecules, that can accrete together and effectively form networks of mutual interactions, in line with Oparin’s droplets. Lancet proposed lipids, oily compounds that spontaneously form the aggregated membranes enclosing all living cells. Lipid bubbles (vesicles) can grow and split much like living cells. This is how Lancet generated the concept “Lipid World” two decades ago.
Based on the computer model they developed, the scientists demonstrated that specific lipid compositions, called “composomes”, can undergo compositional mutations, be subject to natural selection in response to environmental changes, and even undergo Darwinian evolution.
Prof. Lancet comments that such an information system, which is based on compositions and not on the sequence of chemical “letters” as in DNA, is reminiscent of the realm of epigenetics, where traits are inherited independent of the DNA sequence. This fits with the idea that life could emerge before the advent of DNA and RNA.
In their article they in fact delineate a chemical path that leads to the appearance of genetic material in the framework of the oily droplets.
Lancet’s “Lipid World” concept is contingent upon the question of whether there were sufficient oil-like “water hating” molecules in the primordial soup. Here too, the scientists describe a comprehensive literature search, according to which there is a high probability for such molecules to be present on early earth.
This conclusion was reinforced by a very recent study showing that Enceladus, one of Saturn’s moons, has a sub-glacial ocean replete with “water hating” compounds (primordial soup), some of which could form Lipid World-type droplets.
Prof. Lancet contends that these findings, along with innovative model-based computations, show that the probability of life’s emergence is relatively high, including the exciting possibility that Enceladus presently harbours some primary lipid-based life forms.