Theories on the Origin of Life
Conceivably the most central but the least understood biological mystery is how did life originate on this planet? It is the fundamental mystery to many scientific and philosophical thinking as well as trying to ask if we are alone in this entire universe and assuming there is no other extraterrestrial life elsewhere. Can we assume these five events may have taken place when life first originated:
- The origin of life is an outcome of a supernatural event, namely one that is beyond the powers of all physical, chemical and biological sciences as we know them.
- The origin of life is an abiogenesis event meaning life arose from non -living chemicals on Earth more than 3.5 billion years ago. Abiogenesis proposes that the first life-forms generated were very simple and through a gradual process became increasingly complex through the process of evolution and adaptation.
- Life is eternal. It has no beginning or an end. It arrived on Earth at the time of Earth’s origin and began to flourish thereafter due to our ambient and conductive environment that host them.
- Life arose on the early primordial oceans by a series of random aggregation of nucleic acids brought about by nitrogen-fixing, oxygen, hydrogen, phosphorous coming together through continuous discharge of lightning, ultraviolet light into the first DNA / RNA molecules.
- It was implanted into this Earth by extraterrestrial dust from passing comets from the Oort Cloud.
Panspermia theory on life brought to earth by a passing comet from the Oort Cloud:
https://scientificlogic.blogspot.com/search?q=panspermia
- Based on our traditional, religious and philosophical beliefs, for example how heavens, earth and life were created as given in Genesis.
By the time of the Renaissance, there was scientific thinking on the origin of life. There were thoughts that spontaneous generation of animals from putrefying matter was impossible.
During the mid-17th century, the British physiologist William Harvey discovered that every animal comes from an egg. The Italian biologist, Francesco Redi, showed in the latter part of the 17th century that the maggots in meat came from flies’ eggs, deposited on the meat.
In the 18th century an Italian priest, Lazzaro Spallanzani, presented that life can only come from the fertilization of eggs by sperm for the reproduction of mammals. But the idea of spontaneous generation was still there. Even though it was clear that large animals developed from fertile eggs, it was still believed that smaller life-like microorganisms, spontaneously generated from debris. Many felt it was obvious that the omnipresent microscopic creatures generated continually from inorganic matter.
Maggots were prevented from developing on meat by covering it with a fly proof screen. But it was argued that fruit juice could not be kept from fermenting by putting any netting whatsoever over it. There goes that the origin of life is spontaneous that dies hard.
Spontaneous generation was the subject of a great debate between the French bacteriologists Louis Pasteur and Félix-Archimède Pouchet in the 1850s. Pasteur successfully presented evidence that even the most minute creatures came from “germs” that floated downward in the air, but that they could be blocked from access to foodstuffs by suitable filtration. Pouchet argued, forgivably, that life must somehow arise from non-living matter; if not, how had life come about in the first place?
Pasteur’s experiments showed defensively that life does not spontaneously appear from non-living matter. But the American historian James Strick reviewed the controversies of the late 19th century between evolutionists who supported the idea of “life from non-life” and their responses to Pasteur’s religious view that only God can make life. So, the controversies went on, and even till today we are not too sure.
When I was doing a postdoctoral course on evolution at the University of Cambridge in 2018, I brought forward an observation in a technical forum paper discussion on fish that mysteriously appeared in holes and ponds artificially dug up in isolated areas. After many months when rainwater filled up the holes and ponds, fish were found there far away from any river or sea. There were many discussions among the academics at Cambridge with many similar observations and studies done elsewhere and quotes showing the same, but with no satisfactory explanation or conclusion given.
The microbiological conviction that life must always come from preexisting life in the form of cells subdued many post-Pasteur scientists from discussions of the origin of life at all. Many were, and still are, reluctant to offend religious sentiment by researching this provocative subject.
But the valid issues of life’s origin and its relation to religious and scientific thinking raised by Strick and other authors, such as the Australian Reg Morrison, persist today and I think this debate will never end even among the scientists, let alone religious thoughts and beliefs.
Toward the end of the 19th century, Swedish chemist Svante A. Arrhenius proposed that life on Earth arose from “panspermia,” microscopic spores that wafted through space from planet to planet or solar system to solar system by radiation pressure. So did Fred Hoyle (1915–2001) and Chandra Wickramasinghe (born 1939) were powerful proponents of panspermia theory.
In 1974 they proposed the hypothesis that some dust in interstellar space was largely organic or carbon-based, which Wickramasinghe later proved to be correct. Hoyle and Wickramasinghe further contended that life forms continue to enter the Earth's atmosphere, and may be responsible for epidemic outbreaks, new diseases, and the genetic novelty necessary for macroevolution.
This idea, of course, avoids rather than solves the problem of the origin of life. It seems extremely unlikely that any live organism could be transported to Earth over interplanetary or even through vast interstellar distances without being killed by the combined effects of cold, desiccation in a vacuum, and radiation.
However English naturalist Charles Darwin did not commit himself to the origin of life. Darwin wrote about “On the Origin of Species” through Natural Selection. He showed the diversity of organisms and their characteristics that can be explained as the result of natural processes. Darwin published his monumental books On the Origin of Species in 1859 and The Descent of Man in 1871.
Then came the famous British biologist T.H. Huxley in his book Protoplasm: The Physical Basis of Life (1869) and the British physicist John Tyndall in his “Belfast Address” of 1874. Both these scientists defended that life could be generated from inorganic chemicals. But they had extremely vague ideas about how this might be accomplished. The words “organic molecule” means a class of chemicals uniquely of biological origin.
Despite the fact that urea and other organic (carbon-hydrogen) molecules had been routinely produced from inorganic chemicals since 1828, the term organic meant “from life” to many scientists.
Hence, the word organic does not mean it has to be of biological origin. The origin-of-life problem largely reduces to the determination of an organic, nonbiological source of certain processes such as the identity maintained by metabolism, growth, and reproduction as in autopoiesis.
Darwin’s thinking was: “It is mere rubbish thinking at present of the origin of life; one might as well think of the origin of matter.” The two problems are in fact curiously connected. Indeed, modern astrophysicists do think about the origin of matter.
The evidence is undoubted that thermonuclear reactions, either in stellar interiors or in supernova explosions, generate all the chemical elements of the periodic table more massive than hydrogen and helium. Supernova explosions and stellar winds then distribute the elements into the interstellar medium, from which subsequent generations of stars.
In fact, astronomers claim we are made from star dusts generated by a supernova explosion where elements landed as the soil of this earth from which God created man as a living soul by His breath. I believe this is where scientists and religion agree with each other on our origin.
In the 1920s British geneticist J.B.S. Haldane and Russian biochemist Aleksandr Oparin acknowledged that the nonbiological creation of organic molecules in the present oxygen-rich atmosphere of Earth is highly unlikely but that, if Earth once had more hydrogen-rich conditions, the abiogenic production of organic molecules would have been much more likely.
The thinking is, if large quantities of organic matter were somehow synthesized on the primitive Earth, they would not necessarily have left much of a trace today. Our present atmosphere with 21 percent of oxygen produced by cyanobacteria, algal, and plant photosynthesis, and organic molecules would tend, over geological time, to be broken down and oxidized to carbon dioxide, nitrogen, and water.
As Darwin believed, the earliest organisms would have tended to consume any organic matter spontaneously produced prior to the origin of life.
The first experimental simulation of early Earth conditions was carried out in 1953 by a graduate student, Stanley L. Miller, under the guidance of his professor at the University of Chicago, chemist Harold C. Urey.
They made a mixture of methane, ammonia, water vapour, and hydrogen which were continuously sparked by electricity mounted higher in the apparatus. The discharge was thought to represent lightning in the primordial atmosphere.
After several days of exposure to sparking, the solution changed colour. Several amino and hydroxy acids, familiar chemicals in contemporary Earth life, were produced by this simple procedure. The experiment is simple enough to show the presence of amino acids Ultraviolet light or heat was substituted as an energy source in subsequent experiments.
On the primitive Earth much more energy was available in ultraviolet light than from lightning discharges. At long ultraviolet wavelengths, methane, ammonia, water, and hydrogen are all transparent, and much of the solar ultraviolet energy lies in this region of the spectrum. The gas hydrogen sulphide was suggested to be a likely compound relevant to ultraviolet absorption in Earth’s early atmosphere.
Amino acids were produced by long-wavelength ultraviolet irradiation of a mixture of methane, ammonia, water, and hydrogen sulphide. At least some of these amino acid synthesis involved hydrogen cyanide and aldehydes such as formaldehyde as gaseous intermediates formed from the initial gases. The biologically abundant amino acids made readily under simulated early Earth conditions is quite remarkable. If oxygen is permitted in these kinds of experiments, no amino acids are formed. This has led to a belief that hydrogen-rich or oxygen-poor conditions were necessary for natural organic syntheses prior to the appearance of life.
But neither the presence of amino-acid or even the presence of DNA / RNA means the music of life itself. It must be something else that resides in these amino acids or neucleic acids and nucletides that make them alive. See my further arguments here:
https://scientificlogic.blogspot.com/search?q=the+mystery+of+life
Under alkaline conditions, and in the presence of inorganic catalysts, formaldehyde spontaneously reacts to form a variety of sugars. The five-carbon sugars fundamental to the formation of nucleic acids, as well as six-carbon sugars such as glucose and fructose, are easily produced. These are common metabolites and structural building blocks in life today.
Additionally, the nucleotide bases and even the biological pigments called porphyrins have been produced in the laboratory under simulated early Earth conditions. Both the details of the experimental synthetic pathways and the question of stability of the small organic molecules produced are vigorously debated.
Nevertheless, most, if not all, of the essential building blocks of proteins (amino acids), carbohydrates (sugars), and nucleic acids (nucleotide bases which are the monomers can be readily produced under conditions thought to have prevailed on Earth in the Archean Eon.
The search for the first steps in the origin of life has been transformed from a religious/philosophical exercise to an experimental science.
Polymers:
The formation of polymers, long-chain molecules made of repeating units of monomers, is a far more difficult experimental problem than the formation of monomers. Polymerization reactions tend to be dehydrations.
A molecule of water is lost in the formation of a peptide from two amino acids or of a disaccharide sugar from two monomers. Dehydrating agents are used to initiate polymerization.
The polymerization of amino acids to form long protein-like molecules (“proteinoids”) was accomplished through dry heating by American biochemist Sidney Fox and his colleagues. The poly amino acids that Sidney Fox formed were not random molecules unrelated to life. Long polymers of amino acids were also produced from hydrogen cyanide and anhydrous liquid ammonia by American chemist Clifford Matthews in simulations of the early upper atmosphere.
Some evidence exists that ultraviolet irradiation induces combinations of nucleotide bases and sugars in the presence of phosphates or cyanides. Some condensing agents such as cyanamide are capable of being made under simulated primitive conditions.
Despite the breakdown by water of molecular intermediates, condensing agents may quite effectively induce polymerization, and polymers of amino acids, sugars, and nucleotides have all been made this way.
That adsorption of relevant small carbon compounds on clays or other minerals may have concentrated these intermediates was suggested by the British scientist John Desmond Bernal which may have biological significance. Phosphorus, which with deoxyribose sugar forms the mainstay of DNA is integrally involved in cell energy transformation and membrane formation, is preferentially incorporated into organic molecules.
The early ocean and lakes may have been a dilute solution of organic molecules. If all the surface carbon on Earth were present as organic molecules, or if many known ultraviolet synthetic reactions that produce organic molecules were permitted to continue for a billion years with their products dissolved in the oceans, a 1 percent solution of organic molecules would result.
Haldane suggested that the origin of life occurred in a “hot dilute soup.” Concentration through either evaporation or freezing of pools, adsorption on clay interfaces, or the generation of colloidal enclosures called coacervates may have served to bring the organic molecules in question in contact with each other.
The essential building blocks for life were possibly produced in comparatively abundant concentrations, given conditions on the early Earth. Although pertinent, this is more akin to the origin of food than to the origin of life. If life is defined as a self-maintaining, self-producing, and mutable molecular system that derives energy and supplies from the environment, then food is certainly required for life.
Polynucleotides which are polymers of RNA and DNA can be produced in laboratory experiments from nucleotide phosphates in the presence of enzymes of biological origin using polymerases, and a preexisting “primer” nucleic acid molecule. If the primer is absent, polynucleotides are still formed, but they lack specific genetic information.
Once such a polynucleotide forms, it can act as a primer for subsequent syntheses.
Even if such a molecular population could replicate polynucleotides, it would not be considered alive. The polynucleotides tend to hydrolyse in water.
In the early 1980s American biochemist Thomas Cech and Canadian American molecular biologist Sidney Altman discovered that certain RNA molecules have catalytic properties. They catalyse their own splicing, which proposes an early role for RNA in life or even in life’s origins. Only the cooperation of the two kinds of molecules (proteins and nucleic acids) segregated from the rest of the world by an oily membrane makes the growth process of life on Earth possible. The molecular machinery ancillary to the operation of the genetic code, the instructions that determine the linear order of amino acids in proteins from nucleotide base pairs in nucleic acids, namely, the activating enzymes, transfer RNAs, messenger RNAs, ribosomes, etc, may be the product of a long evolutionary history among natural, thermodynamically favoured, gradient-reducing complex systems.
These rules are produced according to instructions contained within the code. The American biophysicist Harold J. Morowitz argued persuasively that the origin of the genetic system, the code with its intricate molecular apparatus, occurred inside cells only after the origin of life as a cyclic metabolic system.
Similarly, the American theoretical biologist Jeffrey Wicken pointed out that replicating molecules, if they appeared first, would have had no impetus to develop a complex cellular package or associated protein machinery and that life thus probably arose as a metabolic system that was stabilized by the genetic code, which allowed life’s second law-favoured process to continue ad infinitum.
The earliest living systems:
Most organic molecules made by living systems inside cells show the same optical activity, that is, when exposed to a beam of plane-polarized light, they rotate the plane of the beam. Amino acids rotate light to the left, whereas sugars, called dextrorotatory, rotate it to the right.
Organic molecules produced artificially lack optical activity because both “left-handed” and “right-handed” molecules are present in equal quantity. Molecules of the same optical activity can be bring together in complementary ways like the stacking of right-handed gloves. The same monomers can be used to produce longer chain molecules that are three-dimensional mirror images of each other; mixtures of monomers of different handedness cannot.
Cumulative symmetry is accountable for optical activity. At the time of the origin of life, organic molecules, corresponding both to left- and right-handed forms, were no doubt formed as they are in laboratory simulation experiments today: both types were produced. But the first living systems must have engaged one type of component, for the same reason that carpenters cannot use random mixtures of screws with left- and right-handed threads to produce a tool.
Whether left- or right-handed activity was adopted was probably a matter of random chance, but, once a particular asymmetry was established, it maintained itself.
Optical activity accordingly is likely to be a feature of life on Earth or on any planet. The probabilities may be equal of finding a given organic molecule or its mirror image in extraterrestrial life-forms if, as Morowitz suspects, the incorporation of nitrogen into the first living system involved glutamine, the simplest of the required amino acid precursors with optical activity.
The first living cells probably resided in a molecular Garden of Eden, where the pre-biological origin of food had guaranteed monomers that were available. The cells, the first single-celled organisms, would have increased speedily. But such an increase was eventually limited by the supply of molecular building blocks. Those organisms with an ability to synthesize scarce monomers, say A, from more abundant ones, say B, would have persisted.
The secondary source of supply, B, would in time also become exhausted. Those organisms that could produce B from a third monomer, C, would have preferentially persisted. The American biochemist Norman H. Horowitz has proposed that the multienzyme catalysed reaction chains of contemporary cells originally evolved in this way.
Multiple theories on life’s origin go on, each scientist proposes his own thoughts, others believe its origin is entirely the prerogative of an Intelligent Design whom we call God, the Maker of all things.
For further reading may I suggest an excellent book called “Origin of Life” by Jim Brooks, B. Tech. M Phil, PhD, C. Chem. FRCS, F. Inst Pet, FGS, Assoc BIT who is a geochemist and an oil explorationist with Britoil. He wrote a very interesting book describing the first moment of the Universe to the beginning of life on Earth in 158 pages. His ideas are an extension of mine.
Another article worth reading was written by the late prolific science writer Dr Isaac Asimov in his book “The Planet That Wasn’t” in his chapter “Silent Victory” how life on Earth began.
We could go on, and on discussing this mystery, but it is already very late into the night into the early hours before dawn, and I need to stop here.
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