Origin of Life - part V

[sotirio]

This is another extract of my origin of life report, presenting slightly more extreme hypotheses and my own conclusions.

Planet Earth: A giant pre-biotic reactor and the hypothesis of symbiosis

Earth, just like any other planet, has unique properties. The distance from the Sun, its axial tilt with the resulting seasonal variations, its magnetic field, the moon, its plate tectonics, the water and carbon cycles and many other parameters are conditions that supported life.
Since the origin could be considered to be a planetary process (4), the open system grey box in figure 4 represents Earth, a dynamic and spatially heterogeneous reactive planet. As subsystems we mainly have the four geospheres from geology; an atmosphere, a hydrosphere, a lithosphere and the biosphere(30). The first three split terrestrial matter into three physical states, whereas the biosphere is only the result of life. It is a dynamic state of order which organises matter and energy cyclic flows among the boundaries of the other three spheres, often dictating the overall kinetics. It's crucial to understand the interactions at the boundaries, for example mass and energy transfer occurring at the interface of the oceans and the atmosphere. In addition, in a dynamic and distributed parameter model system like planet Earth, the effects of variations over the interfaces should be examined further. Another subsystem which could have caused a shift in thermodynamic conditions is the cryosphere, acting as a protective layer-external artificial membrane- on top of the hydrosphere in some regions. Unlike other materials, the melting curve for water has a negative gradient on the phase diagram, as liquid water is denser than ice.
It is interesting to note that regardless of the scale, matter forms stable structures that operate as a network. For example, on the atomic level molecules form due to covalent and ionic bonds. In fact, stable forms of giant ionic and metallic lattices have been observed. Eukaryotic cells consist of a nucleus, a membrane and all their specialised organelles, each performing a different function. Endosymbiosis is considered as the process by which prokaryotes evolved to the first eukaryotic cells (31). Nevertheless, this is universally true for any scale, encompassing molecular chemistry to planetary systems. As an everyday example, in human societies we choose to cooperate with people for safety, stability and prosperity. The overall goals are common and simple; firstly, survival and secondly evolution. Life continuum is a story of progression via information that ensures its existence by symbiotically cohabiting within the boundaries of its ecosystem.
Oparin very interestingly noted that autotrophs were too complicated to be the first cells to exist (32). By generalising his statement, this could be translated as another property of living organisms. Initially, some functions are performed externally and if deemed desirable they are then adopted and inherited through replication and thus evolution. Cairns-Smith proposed that the replication mechanism by inorganic crystals, such as clay, was the origin of primitive genes (33). According to the author, a gradual “take-over” of the evolved crystallisation process by organic macromolecules is then considered to have occurred. These mineral surfaces may have served as concentrating agents, excluding water from life’s monomers transition to oligomers and eventually polymers (21). Another good analogy would be heterogeneous catalysis and adsorption in porous rocks. It's not a coincidence that in chemical reactors the rate is increased with heterogeneous catalysts, taking advantage of their large surface area compared to their volume. Imagine, having "smart" selective nano-scale catalysts that are monitored from the control panels of a chemical plant. Clearly, the correlation between biological processes and engineering is undeniable; the question that needs to be answered is how will engineering approach nature in the future.

Panspermia

This hypothesis aims to couple the whole pathway from planet formation to the migration of life through space, dating back to the early 1900s (34).
Carl Sagan and many other scientists argued that the magnitude of the universe permits the existence of extra-terrestrial life (35, 36). For instance, the Drake equation, although it relies on unverified assumptions, provides a guesstimate to the odds of finding communicating civilisations in the universe. Over the past few decades, we discovered more Earth like planets that could support life (28) and a good example of a solar system with a habitable zone is the TRAPPIST-1 system (37).
The universe is about 13.8 billion years old, but our solar system formed approximately 4.6 billion years ago, according to radiometric dating of meteorites and moon rocks (38). The hypothesis of panspermia claims that primitive life may have formed extra terrestrially in a distant galaxy far far away and migrated through space. The dominant source of exogenous organics to early earth is believed to be interplanetary dust particles. This sounds plausible, given the existence of the universe billion years before the formation of our solar system, meaning that the probability that life emerged somewhere else is much more likely. For example, it is widely accepted that nucleobases and amino acids, the building blocks of proteins, landed on Earth during the heavy bombardment with carbon-rich meteorites (39) in the Hadean Eon. While the emergence of life was a marathon and not a sprint, this cataclysmic event could speed it up significantly, as it supplied the Earth with large oceans and a moon -giant impact hypothesis (40), both of which were necessary steps for life formation.
Moreover, bacteria have been detected in the international space station (ISS), meaning that life effectively survives the journey from the earth into space. This reversible mass transfer of organic matter and also prokaryotic microorganisms is sufficient to suggest that it assisted on the development of life on Earth to a large extent. At this point, the probability that LUCA was alien is not farfetched at all. In terms of a galactic thermodynamic system, this possibility offers a broader picture with higher chances for the emergence of life. On the other hand, planet Earth and its external energy influx from the sun, as well as any internal sources like volcanic eruptions decrease the probability by orders of magnitude. After all, the laws physics and chemistry are universal, why can't biology be the same?
Even though panspermia could theoretically answer the origin of life on Earth, it fails to consider how and where it emerged in the universe. On the contrary, it opens the field to more degrees of freedom, removing the constraint of the planetary boundary. Although, environmental criteria must be fulfilled for life to arise, survive and evolve, therefore astrobiology is crucial to look for life in space at the right direction using high-tech tools.

Intelligent Design and Simulation Hypothesis

In fact, speculation could lead to the hypothesis of intelligent design that has been directly or indirectly seeded throughout the cosmos. Meyer argues that certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection. The key to this hypothesis is information, which is carried by DNA, functioning like a software program, coding life wherever it migrates. He criticises evolutionary theory with the idea that random genetic mutations cannot increase the information content in the genome.
Before dismissing Meyer's hypothesis, one useful thought experiment would be the most efficient method to colonise the expanding universe. Surely, it wouldn't be with spaceships and astronauts with biological bodies, as our adaptive flexibility is limited to the conditions of our host planet and any identical options. However, unlike humans, the RNA ribozyme could replicate and evolve into different forms, responding to its surroundings. Furthermore, man-made space-ships require fuel, but comets and asteroids rely on the force of gravity to cover vast distances. The main difference between these two options is the degree of randomness. In the second case, physical forces act as external disturbances that influence the path of tiny “microbe spores” that are propelled through space. However, both RNA and DNA still have limitations in the form of mutations and are vulnerable to the extreme environmental conditions in outer space. To conclude this section, experimenting with DNA would allow us to uncover any hidden historical evolutionary information that has been waiting for billions of years.
My hypothesis is the profound interrelation between intelligence and evolution and their variable rate of causality. In a 'primordial soup' or anywhere else that was kinetically and thermodynamically feasible for life to arise, simple biopolymers emerged. Their subsequent evolution into DNA was the rate-limiting step in this multistage process. As soon as DNA-based life forms evolved, they exploited the rising oxygen concentrations in the atmosphere, leading to the Cambrian explosion and the diversity of life. Perhaps, intelligence is not the right word to describe the cell’s ability to survive and thrive in a dynamic environment, but I cannot think of a better way of quantifying and defining evolution’s rate constant.
Another alternative extreme scenario is that our universe could be a simulation from a post-human civilisation (41). Given the exponential growth in computing power in the last decades, this hypothesis is not science fiction anymore, as Elon Musk portrayed his view on the topic in 2016. Arguably, if it is indeed a simulation, then it would have some goals and objectives that would help us understand why life evolved and what exactly is trying to verify; provided we manage to figure the rules out.
Once again, like panspermia, tracing the origin of life with these two options has two main drawbacks. It fails to really consider where life arose in the first place and more importantly it is extremely difficult to test them.

Destination Mars – Empirical experiments in planets within the habitable zone

A viable experiment to test panspermia is planet Mars. As space exploration gains momentum, it is highly likely that a mission to Mars would finally end the debate of whether or not there is dormant or even active life in its hostile environment. The first step is to identify locations that provide the essential ingredients of life (42) (e.g. liquid water) and also exist here on Earth and are inhabited with extremophiles. Detection of microbial unicellular life with the same universal properties that dates back to over 3 billion years ago would provide conclusive evidence to suggest that panspermia did indeed occur in our solar system. Having a second planet so close to Earth which is not identical to ours that supports life would prove that life is abundant in the universe, but biological evolution to complex life requires more rate-limiting steps than simple unicellular life. Therefore, this would suggest that the planetary conditions are responsible for the discrete evolutionary step between prokaryotic and eukaryotic life.

Conclusion

Despite not having the precise scenario for the emergence of life, the study shows that the mechanism behind it is survival which ultimately results in evolution. Life is about continuity. Everything is connected by a long unbroken string of continuous existence and is stored safely in the DNA. Hence, it will not be surprising if replicating polymers existed in a pre-RNA world that preserved this information.
A living organism has a transient path between two states that we conventionally labelled as birth and death. The path is unique in each case, giving rise to individuality. Life follows a path function, just like heat and work in thermodynamics. These are properties whose values depend on the transition of a system from the initial state to the final. On the other hand, the emergence of life is a state function, an inevitable low probability event in the vastness of the universe. It is inevitable because not only it exists in our planet, but also thrives and adapts to variable and sometimes extreme conditions through time and space, like ice ages and deep sea hydrothermal vents, creating a life cycle which will never cease to exist until the planet runs out of energy sources. This special ability arises from its nano-level structural properties, specifically the membranes, as well as the functions of the organelles and the nucleic acids, inside cells. Perhaps it could be argued that the invention of the human language primarily and the internet later on were just imitations of natural biological communication processes. The bottom line is that regardless of what we might discover in the years to come, life has evolved to be extraordinary and extremely diverse in our very own pale blue dot.

Thanks for making it this far :)
If people are interested I will add the rest of my work in the near future.

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