1.9 Life on Earth

The traditionalist view that the rich forms of structures in the worlds could only be the product of divine intelligence¹ has been effectively counteracted with the advent of scientific naturalistic interpretations. The same approaches that were developed to describe the emergence of complexity equally apply to the emergence of ‘life’. 

As mentioned above, the Earth itself, with all that exists on its surface, is a giant dynamic open system, kept far from equilibrium by the continuous flow of energy from the sun. This energy flow generates dynamic ordered systems kept stable by the ongoing energy flux and by exporting thermal energy back into space. Thus, the Earth locally evades the degenerative effects of the Second Law of Thermodynamics by exporting entropy (ie, disorder) into space. 

Prominent in the increase in complexity with higher levels of merging phenomena is the appearance of life on Earth. The perspective that Erwin Schrödinger gave in his lectures in 1943 in Dublin is highly relevant. He was already a well-established physicist and Nobel prize winner. He asked then “How does an organism concentrate streams of order on itself and thus escape the decay of atomic chaos mandated by the Second Law of Thermodynamics?”, a question that came to be known as the Schrödinger ‘paradox‘.² He proposed the idea that living organisms feed on negative entropy, ie, they produce order by taking it from the environment³.

An influential publication by the Nobelist Jacques Monod⁴ highlighted this perspective by proposing that that life is the result of natural processes by ‘pure chance’. This perspective compels us to refuse the simplistic idea of predetermination in the human existence. He added “the biosphere does not contain a predictable class of objects or of events but constitutes a particular occurrence, compatible indeed with first principles, but not deducible from those principles and therefore essentially unpredictable“. This perspective is consistent with the idea suggested above that the universe is new at every moment.

As I described above, modern physico-chemistry shows how dissipative phenomena can generate order from disorder and how a system can be kept in a state of transient stability (metastability) of dynamic equilibrium by continuous flow of energy⁵. Indeed, reaction-diffusion equations describe well many events in biology including aspects of morphogenesis, pigmentation patterns in skin, ecological invasions, spread of epidemics, tumour growth, etc⁶.

The history of life on Earth is long and complex but the biosphere consists in interlocked, overlapping metastable systems, far from equilibrium, involving selection processes, with emergence of superimposed layers of organisation with new properties⁷.

The specific steps of the origin of life are still unclear, but there are several lines of research that are beginning to give plausible explanations. These steps are likely to have involved:
   [1] the formation of new organic molecules from the ongoing flow of chemical energy;
   [2] their self-assembly and selection into macromolecules with properties including self-replication and autocatalysis;
   [3] their segregation into separate compartments by molecular membranes facilitating the formation of systems with dynamic stability.

The origin of life is thus attributed to the appearance of metastable chains of chemical reactions, forming prebiotic molecules⁹. In order to survive, they must have become segregated into compartments, probably within bubbles in hydrothermal vents deep in primordial oceans. In turn, this led to the appearance of interdependent chemical reactions, dynamically metastable, representing primitive “metabolic” processes. Within such compartments, these primordial chemical reactions transformed chemical energy into kinetic energy for the transport of substances and for sustaining mechanical events. These compartmentalised metabolic processes represented the most primitive living cells (‘protocells’)¹⁰.

Compartmentalised metabolic networks can oscillate and cells can form communities on the basis of these rhythms¹¹. This indicates that living systems have underlying oscillatory mechanisms from single cells up¹². Indeed, in his classic short paper, Anderson had already pointed out that “most methods to extract energy from the environment in order to set up a continuing, quasi-stable process involve time-periodic machines, such as oscillations and generators, and the processes of life work in the same way.”¹³ 

Jeremy England suggests a way in which energy driven processes generate more adaptable robust self-organised structures. According to him matter – living or not – will, in some circumstances, evolve over time to efficiently harness specific environmental energy sources. He called this ‘dissipative adaptation’, proposing that some distinctive features of life arose through a non-biological process of selection, with chemical or physical structures using a source of energy to reduce disorder without themselves being destroyed. Such a process catalyses the formation and growth of similar structures¹⁴. 

The last universal common ancestor (LUCA) of living cells appeared about 3.8 billion years ago. From this ancestor all present living beings evolved as an uninterrupted stream of life on Earth. More than 2 billion years ago cyanobacteria, capable of photosynthesis¹⁵, began releasing oxygen into the world’s oceans, which combined with dissolved iron, produced haematite or magnetite. Oxygen released into the atmosphere was absorbed by and reacted with minerals in the crust, resulting in nearly all the earth’s iron ore forming more than 1.8 billion years ago¹⁶.

The accumulation of oxygen profoundly modified the redox chemistry of the Earth and the evolution of the biosphere, including complex life. Oxidation is destructive for living cells and life survived by symbiosis between the primitive bacteria sensitive to oxygen and ‘aerobic’ bacteria which could survive and use oxygen in their metabolism. Aerobic bacteria, probably an alpha-proteobacterium, or perhaps aerobic Archaea, were internalised by larger anaerobic cells via a process of endosymbiosis¹⁷ and became mitochondria, intracellular organelles that are the powerhouses of cells, extracting energy from sugars with oxygen. This process underlies aerobic metabolism in nearly all living organisms today.

Bacteria do not have a nucleus (hence they are called prokaryotes). At some stage around 2.0 bya, during the adaptation to the oxygen surge, some prokaryotes acquired by a similar endosymbiosis process, a primordial bacterium, already containing nucleic acids (RNA and DNA), which became the nucleus, a further separate compartment with replicating DNA, the machinery of genes. These cells became ‘eukaryotes’ ie, cells with a nucleus.

Some evidence suggests that key eukaryotic features were acquired all at once, rather than gradually¹⁸, since all eukaryotes have the exact same set of organelles familiar to anyone who has studied cell biology: nucleus, nucleolus, ribosomes, rough and smooth endoplasmic reticulum, Golgi apparatus, cytoskeleton, lysosome and centriole.

Plants and a few other photosynthetic eukaryotes probably arose through a separate endosymbiotic event leading to chloroplasts, organelles in the plant cell that probably evolved from endosymbiotic photosynthetic cyanobacteria and, like mitochondria, contain their own DNA. Chloroplasts generate oxygen from carbon dioxide and water using sunlight as the energy source for synthesising ATP and NADPH, which in turn provide chemical energy for most intracellular metabolic reactions. In the process, carbon dioxide is converted into carbohydrates.

Living cells can be regarded as open dissipative systems. The flow of energy in animal cells comes from the metabolism of oxygen in the mitochondria which generates the energy for most of the ongoing chemical reactions in the cell. Thus the cell maintains a dynamic equilibrium, with heat production as the unavoidable by-product according to the Second Law of Thermodynamics. 

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1. For example, William Paley (1809) Natural Theology: or, Evidences of the Existence and Attributes of the Deity. This link has the full text. ↩︎
2. Not the same thing as Schrödinger’s Cat paradox… ↩︎
3. Erwin Schrödinger (1944): What Is Life? The Physical Aspect of the Living Cell. Cambridge University Press. The book was based on a course of public lectures delivered by Schrödinger in February 1943, under the auspices of the Dublin Institute for Advanced Studies, where he was Director of Theoretical Physics, at Trinity College, Dublin.
   See also Carl Zimmer (2021) Life’s Edge: The Search for What It Means to be Alive. Dutton. ↩︎
4. Jacques Monod (1970/1971): Le Hasard et la Nécessité: Essai sur la philosophie naturelle de la biologie moderne / Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology. Alfred A. Knopf. ↩︎
5. See Stuart Kauffman (1995): At Home in the Universe: The Search for Laws of Self-Organization and Complexity. Oxford University Press. ↩︎
6. For examples, see Hans Meinhardt, (1982) Models of Biological Pattern Formation, Academic Press;
   James D Murray (2013) Mathematical Biology. Springer.  ↩︎
7. See, for example, P Chvykov et al (2021): Low rattling: A predictive principle for self-organization in active collectives. Science 371 90-95. Click here to download the PDF file.
   For a general overview, see: https://en.wikipedia.org/wiki/Biological_organisation ↩︎
8. See also the more general concept of ‘self-organisation’: https://en.wikipedia.org/wiki/Self-organization ↩︎
9. For examples, see: https://en.wikipedia.org/wiki/Abiogenesis ↩︎
10. For an extended discussion, see: https://en.wikipedia.org/wiki/Protocell ↩︎
11. Albert Goldbeter (1996): Biochemical Oscillations and Cellular Rhythms. Cambridge University Press. ↩︎
12. eg, Campbell, K. et al (2015): Self-Establishing Communities Enable Cooperative Metabolite Exchange in a Eukaryote. eLife 4:e09943. ↩︎
13. Anderson, PW (1972): More Is Different: Broken symmetry and the nature of the hierarchical structure of science. Science, 177(4047), 393–396. Click here to download an extended discussion of this paper. ↩︎
14. See Jeremy England (2020): Every Life Is On Fire – How Thermodynamics Explains the Origins of Living Things. Basic Books / Hachette. ↩︎
15. Recently, the oldest fossil evidence of photosynthesis has been found inside cyanobacteria that lived around 1.75 billion years ago. See Dermoulin CF et al (2024): Oldest thylakoids in fossil cells directly evidence oxygenic photosynthesis. Nature 625, 529-534. ↩︎
16. See https://en.wikipedia.org/wiki/Geological_history_of_oxygen and https://en.wikipedia.org/wiki/Great_Oxidation_Event ↩︎
17. See also: https://en.wikipedia.org/wiki/Symbiogenesis ↩︎
18. For example, see Vivianne Callier (2023): Where the heck did all those structures inside complex cells come from? ASBMBTODAY. ↩︎

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