Reflections on the Nature of "Living" Systems

[Text below adapted from my college astronomy course discussion contributions:]


//Conditions Supportive of Life//
What conditions does Earth have that seem necessary to support the existence of living organisms? Be specific, and relate these conditions to the history and astronomical context of our planet.

Although other combinations of chemical compounds may possibly lead to self-organization, metabolic activity, and replication (and therefore evolution) as xenobiologists are currently studying, the most basic necessities for life in the form we are familiar with, which are provided for on Earth, include:

• The Sun, as a source of electromagnetic energy necessary for photosynthesis and maintaining habitable temperatures on the Earth's surface (i.e. keeping water in its liquid state beyond the Archean Eon, 4.0-2.5 Ga; Note: "Astronomers think that the sun had about 70–75 percent of the present luminosity, yet temperatures appear to have been near modern levels even within 500 Ma of Earth's formation [> 4.04 Ga], which is puzzling (the faint young Sun paradox).  The presence of liquid water is evidenced by certain highly deformed gneisses produced by metamorphism of sedimentary protoliths. The equable temperatures may reflect the presence of larger amounts of greenhouse gases than later in the Earth's history.  Alternatively, Earth's albedo may have been lower at the time, due to less land area and cloud cover.").  Additionally, the Sun's electromagnetic radiation (reduced to a "healthy" level due to the Earth's magnetic field and ozone layer) accelerates evolution by introducing errors in DNA and RNA encoding sequences, a small percentage of which lead to beneficial adaptations [see Genetic Variation].
• A very wide variety of types of elements and molecules from one or more supernovae, (reactants and catalysts) needed for complex chemical reactions, which provided the diverse array of chemical interplay and structures needed for the random creation of biochemical precursor compounds (i.e. amino acids, nucleic acids) necessary for a successful selection of chemically interacting components that could inherently self-organize, self-sustain through metabolic reactions, and replicate (via RNA or simpler precursors such as PNA, GNA, or TNA).
• Liquid water, provided by volcanic activity as well as ice-containing asteroids, meteorites, and proto-planets (particularly during the Late Heavy Bombardment phase of Earth's history, 4.1-3.8 Ga), as a highly efficient medium for the suspension, free movement, and interaction of chemical compounds necessary for the formation of the first organic compounds (by allowing a very high frequency of random encounters of inanimate chemical compounds to occur), and to eventually continue providing cellular life the capacity for homeostasis (via self-containment within a membrane) and the medium in which to carry on cell processes, including metabolic chemical reactions.
• An atmosphere, providing the containment (i.e. avoiding loss into space) of water vapor, a positive pressure environment necessary for cellular life to survive beyond the oceans, and a major source of molecules (such as carbon dioxide and nitrogen) necessary for the metabolic activity of more complex unicellular, and eventually multicellular, organisms utilizing photosynthesis.

How likely do you think it is that other planets in the universe have, or have had in the past, those conditions that seem necessary to support the existence of living organisms? Explain why you think so.

The following quote, which I used part of in my Week 2 discussion about the likelihood of "intelligent" life elsewhere in the universe, provides support for the idea that life must (extrapolating statistically) exist in other locations in the universe because very similar conditions to those on Earth exist in countless other solar systems in the universe:

"The chemistry of life may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10–17 million years old.  According to the panspermia hypothesis, microscopic life—distributed by meteoroids, asteroids and other small Solar System bodies—may exist throughout the universe.  Nonetheless, Earth is the only place in the universe known to harbor life.  Estimates of habitable zones around other stars, along with the discovery of hundreds of extrasolar planets and new insights into the extreme habitats here on Earth, suggest that there may be many more habitable places in the universe than considered possible until very recently.  On 4 November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy.  11 billion of these estimated planets may be orbiting sun-like stars.  The nearest such planet may be 12 light-years away, according to the scientists." [https://en.wikipedia.org/wiki/Planetary_habitability]

I personally concur with the panspermia hypothesis, that forms of basic animate matter (i.e. "life" and/or its precursor components) exist throughout the universe.  It is quite plausible that Earth was "seeded" with very basic form(s) of animate matter by one or more space bodies entering the Earth's atmosphere during its first billion years or so of existence.  On Earth, and on other planetary bodies in the universe with the right conditions, there as a "nursery" environment that permits the development of more complex animate matter and an evolutionary process, through natural selection, providing ever more complex forms of life to develop.

//Variety Possible in Forms of "Life"//

Many people often forget that there is a vast middle-ground of possibilities when it comes to the "variety spectrum" for animate systems.  For them there is either little, if any, forms of life beyond our planet or solar system, or there are countless other intelligent species in the universe that are generally very similar in their biochemistry and physiology to homo sapiens.  Yet, xenobiologists (and astrobiologists) have made significant progress in the last decade in expanding our realization of the vast variety of forms in which "living" things can potentially exist—forms of animate systems that are not carbon based, use a different molecular liquid besides water to provide an emulsion medium for metabolic-related chemical reactions, and even perhaps "life" that has advanced beyond biochemistry altogether (e.g. self-organized and evolving electromagnetic energy matrices that take full advantage of the significant evolutionary freedom the quantum mechanical characteristics of matter-energy systems provide at the microscopic level (the average photosynthetic efficiency in plants and photosynthetic bacteria is a staggeringly high ≥90-98%^, as compared to our most recent "cutting-edge" advance in solar cell efficiency in the lab of 46.0%, because those biochemical systems provide for the quantum process of photonic energy pathway self-selection called "quantum walk"*).

* "A phenomenon known as quantum walk increases the efficiency of the energy transport of light significantly. In the photosynthetic cell of an algae, bacterium, or plant, there are light-sensitive molecules called chromophores arranged in an antenna-shaped structure named a photocomplex. When a photon is absorbed by a chromophore, it is converted into a quasiparticle referred to as an exciton, which jumps from chromophore to chromophore towards the reaction center of the photocomplex, a collection of molecules that traps its energy in a chemical form that makes it accessible for the cell's metabolism. The particle's wave properties enable it to cover a wider area and try out several possible paths simultaneously, allowing it to instantaneously "choose" the most efficient route, where it will have the highest probability of arriving at its destination in the minimum possible time. Because it takes place at temperatures far higher than quantum phenomena usually occur in, quantum walking is only possible over very short distances, due to obstacles in the form of destructive interference that will come into play. These cause the particle to lose its wave properties for an instant before it regains them once again after it is freed from its locked position through a classic "hop". The distance towards the center is therefore covered in a series of conventional hops and quantum walks." [Source]

^ "Plants 'seen doing quantum physics'"; "Quantum Biology: Better Living Through Quantum Mechanics - The Nature of Reality"; "Quantum coherent energy transfer over varying pathways in single light-harvesting complexes"; "Environment-Assisted Quantum Walks in Energy Transfer of Photosynthetic Complexes"