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"

Highlights of the History of Astronomy and the Basics of Solar System Astronomy

Historical:

• The ancient Babylonians kept vast written records of astronomical data.
• Since the 7th century B.C., the Chinese kept highly accurate records of astronomical data.
• Plato and Aristotle formulated a geocentric model of the solar system describing the Earth as the center, with the sun and other planets revolving around the Earth in perfect circular orbits and the planets simultaneously having epicyclical orbits about their solar orbits to explain "retrograde motion" of the planets observed from Earth.
• In the 2nd century B.C., Hipparchus improved the geocentric model slightly, made the first (relatively) precise observations of stars, and developed the apparent magnitude scale measuring the apparent brightness of a star on a scale of 1 (brightest) to 6 (faintest).
• In the 3rd century B.C., Aristarchus was the first to propose a heliocentric model of the solar system (in which the sun is the center, and the planets revolve around the sun) but his work was largely ignored.
• Ptolemy's sophisticated and far more detailed improvement on the geocentric model was so successful that it remained the near-universally accepted model of the solar system until the Renaissance.
• During the Renaissance, Copernicus developed a detailed heliocentric model of the solar system utilizing a great deal of mathematics that successfully predicted the astronomical patterns of solar-body movements, and whose work was built upon by Galileo Galilei and Johannes Kepler.
• Galileo, who developed the first relatively powerful telescope of the time, was the "father" of observational astronomy, and through his telescopically-collected observations discovered four moons orbiting Jupiter, that the moon had craters, the sun had "sunspots" (which he happened to correctly explain the nature of), observed that Venus (from the perspective of Earth) went through luminary phases similar to the moon, and used his observational evidence to directly support the validity of the heliocentric model.
• Later, Kepler used the couple decades of accurate solar observational data collected by Tycho Brahe and his own intellectual conceptual insights to develop his three law's of planetary motion (1. The orbit of a planet is an ellipse with the Sun at one of the two foci, 2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time, 3. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit).
• Then came along Isaac Newton, who developed the "universal law of gravitation," which very precisely explained mathematically the heliocentric model movements of solar-bodies and made extremely accurate predictions for the future motions and positions of solar-bodies.

Non-Historical:

• Only approximately a maximum of 2,000 stars are visible with the naked eye.
• The Earth's average diameter is 7,918 miles.
• The solar system has a diameter of approximately 9 trillion miles.
• 1 lightyear ≈ 5.88 trillion miles.
• The radius of the observable universe is approximately 14 billion lightyears.
• The apparent encompassing sphere of the heavens about the Earth is called the "celestial sphere."
• 88 constellations are officially recognized by the IAU; that star patterns not formally considered constellations are called "asterisms."
• The apparent path of the sun across the celestial sphere is called the "ecliptic."
• Modern astronomers use a "photometer" and an apparent brightness scale that ranges from -30 to +31? (+31 was assigned to the faintest object detected by the Hubble telescope) {each increment = a ratio of 2.5 from the next increment in degree of brightness}, the Sun measures -26.75 on this scale, and the next brightest star, Sirius, measures in at -1.44.
• Astronomers use "declination" (the angular measure above or below the celestial equator) and "right ascension" (angular measure in units of "hour" {1 hour = 1.5°} relative to the "celestial meridian" (0° in longitude) to define the location of astronomical objects.
• The point directly above (90° perpendicular to the horizon at your current location) is called the 'zenith.'
• A star is said to "culminate" (reaches its highest altitude in the sky) when it is on the celestial meridian.
• The daily paths of stars around the celestial axis are called "diurnal circles."
• To find the "North Star," Polaris, you can use the 'pointer' stars, Dubhe and Merak (which are at the end of the 'bowl' of the Big Dipper).
• The stars that never 'set' below the celestial horizon in the Northern/Southern hemisphere are called "North (or) South circumpolar stars" respectively.
• The band about 16° wide around the sky centered on the 'ecliptic' is called the 'zodiac,' which ancient astrologers divided into 12 constellations, or "signs," each taken at 30° increments of longitude.
• The Earth’s geographical equator remains tilted at about 23.4-23.5° to its orbital plane about the sun.
• The 'vernal equinox,' which occurs about March 20, is the Sun’s position as it crosses the celestial equator going north and is the point on the celestial sphere chosen to be the 0h measure of right ascension.
• The 'autumnal equinox,' which occurs about September 23, is the Sun’s position as it crosses the celestial equator going south.
• During the equinoxes, day and night are equal in length.
• The 'summer solstice,' which occurs about June 21, and the 'winter solstice,' which occurs about December 21, are the most northern and most southern positions of the Sun during the year in the northern hemisphere, and that at these times we have the longest and shortest days, respectively, in the northern hemisphere.
• There are two measures of "day": the 'solar day' (measuring the time interval of Earth’s rotation using the Sun for reference) and the 'sidereal day' (measuring the time interval of Earth’s rotation using the stars for reference).
• A sidereal day is 23 hours, 56 minutes, 4 seconds long, requiring the use of leap-years and leap-seconds.
• The Earth’s axis of rotation shifts extremely slowly around a imaginary 'cone' in space once about every 25,800 years (which is called "precession") and is caused mainly by the tug of the gravity of the Sun and Moon on Earth’s equatorial bulge.
• The Arctic Circle and Antarctic Circle mark the southernmost and northernmost latitude, respectively, at which the sun can remain continuously above or below the horizon for 24 hours (at the June solstice and December solstice respectively).
• The Tropic of Cancer and Tropic of Capricorn are the northern and southern latitudes, respectively, at which the sun reaches zenith only one time a year.