The Origin of Life: Theories

The jury has been out for quite some time now. When will it be back?

The religious colleague wanted at all cost to convince the others of the existence of God: “Who created you?” “Our parents,” was the reply. “But who created your parents?” “Their mothers and fathers?” – and it went on with further questions about the grandparents, great grandparents… And that would eventually lead to the chicken or the egg causality dilemma.

We are landed with two diametrically opposite views.

Religions have had recourse to metaphysics to solve that mystery; in all cultures and civilization, it was impossible to escape from the principle of cause and effect. Anything that exists must have a ‘creator’ and we have built up in our brain a sophisticated psychological module, which would subserve this belief. Our God, to whom we have granted all the attributes of an ever-powerful Almighty, created the universe and life out of the void. Most of us were satisfied with this religious theory of spontaneous generation of life.

But modern scientists, scoffing at this idea, scrutinize and analyze man, that being supposedly created by God: there are too many loopholes for such a creature is too cruel, too full of paradoxical behaviours to have been the perfect product of a supreme being. They are looking for alternative theories to explain the blossoming of life on the blue planet — the coming together of simple chemical molecules, formed in the cauldron of an ever-expanding universe, which would gradually become more complex – in a primordial soup-billion of years ago.

The primordial soup

The invention of the microscope was a boon to scientists. ‘In 1768, Lazzaro Spallanzani demonstrated that microbes were present in the air, and could be killed by boiling. In 1861, Louis Pasteur performed a series of experiments that demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media, but could only appear by invasion from without.’ So there are microbes in the atmosphere – but the problem is how did they come to be here?

On 1 February 1871, Darwin opined that the original spark of life may have begun in a “warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity present, that a proteine compound was chemically formed ready to undergo still more complex changes”; and these simple microbes will be the harbinger of future biological complexity that will evolve into mammals. That’s how physical evidence has been found in ‘biogenic graphite in 3.7 billion-year-old metasedimentary rocks from southwestern Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia, reinforcing the concept that very simple organic molecules, followed by unicellular organisms were first formed on our blue planet more than 3 billion years ago.’ At that time the atmosphere was a “gigantic, productive outdoor chemical laboratory”. But where did these simple chemical compounds form?

Pre-cellular molecules

In her youth, Earth suffered a series of brutal bombardments and celestial collisions; now she is safer. One major hypothesis is that life-molecules started in deep intergalactic space. This is the theory of Panspermia: having been formed somewhere in interstellar space, life in the form of very simple or complex organic molecules or microbes were hitch-hiked on meteorites or rocks blasted from other planets. Thousands of years later, due to weathering, the inner core of those meteorites containing molecules or microbes became exposed and liberated to surrounding fertile soup. But those primordial molecules might have come from our blue planet itself.

‘Metabolism first’ rather than ‘RNA first’ (gene) theory: Robert Shapiro, Professor Emeritus of Chemistry at New York university, believing in ‘some self-sustaining and compartmentalized reaction of simple molecules’ summarized the “primordial soup” theory of 1924 of Alexander Oparin and J. B. S. Haldane in its “mature form” as follows:

1. “The early Earth had a chemically reducing atmosphere – (absence of oxygen).

2. This atmosphere, exposed to energy in various forms, produced simple organic compounds (“monomers”).

3. These compounds accumulated in a “soup” that may have concentrated at various locations (shorelines, oceanic vents, etc).

4. By further transformation, more complex organic polymers — and ultimately life — developed in the soup.”

In 1952 Stanley L. Miller and Harold C. Urey, supplied evidence of that ‘soup’ theory by demonstrating how organic molecules could have spontaneously formed from inorganic precursors, under conditions like those posited by the Oparin-Haldane Hypothesis. The now-famous Miller-Urey experiment used a highly reducing mixture of gases — methane, ammonia and hydrogen — to form basic organic monomers, such as amino acids.

Those more complex molecules somehow or other would surround themselves with permeable or semi permeable membranes and gradually the prototype of cells will evolve – after billion of years – with RNA (ribonucleic acid) incorporated inside.

The first spark of life

Another theory trying to explain the origin of life posits that billions of years ago it was the deep chill. Our planet had a white mantle; frozen into silence, due to a milder sun, inorganic or organic molecules were deep below; ‘our planet had inherited the oceans, liquid laboratories that run trillions of chemical experiments per second’, well protected from outer ultraviolet or all sorts of toxic rays from outer space. Did they have time to interact to form complex molecules under that ice cover, – and kickstarted some wonderful combinations that would ignite the first spark of life?

Another contender is that of submarine hydrothermal vents, thousands of meters below sea level, known as the deep sea vents. Here warm water circulates in pitch-dark environment. There is no oxygen or light, yet there are all sorts of blind organisms crawling and living in an ecosystem of their own. They thrive not on oxygen but on hydrogen sulphide, iron and nickel sulphides escaping from the slits between the sea rocks. Could that rich thermal and chemical environment with catalysts have had the opportunity to invent the first life molecules billion of years ago?

RNA and Replicators

The RNA world (ribonucleic acid) is an important biochemical intermediary in the building of the first block of life – to produce both protein and DNA (deoxyribonucleic acid – our heredity modules). But the flip side is that DNA needs protein to be manufactured – and protein needs DNA to be replicated. It is believed that RNA were formed first and acted as intermediary, as it has the memory to produce and replicate and would act as a catalyst to manufacture proteins. Gradually DNA and proteins took off and surpassed in importance RNA. But RNA still lives in the form of a template and serves replication purposes. How did the RNA arise first, spontaneously? In 1970s some scientist did produce RNA out of simple aldehyde and ammonia – giving rise to molecules of RNA and simple lipids! Hence the belief that RNA might have been around first, long before some other simple or complex metabolism: it is the ‘RNA first’, and ‘Metabolic later’ theory.

There was a chemical cocktail forming in our primordial seas, it needed a strong flash of energy to transform it into a replicator, a combination of molecules that could send versions of itself into the future, for heredity is passed on from generation to generation of individuals by RNA and DNA. The question is how and where did these complex molecules learn this replication strategy. All of us do know something about replication. Our table salt (Sodium Chloride, NaCl), and many other inorganic elements, when dissolved in water and allowed to dry up will form the same crystals repeatedly. And when organic – carbon containing – molecules started forming they took a leaf from the book of their inorganic neighbours. So it is being suggested that that was how complex organic molecules using slabs of clay as scaffold would have transferred the latter’s concept of repetitive technology into the DNA. And one good day the RNA/DNA would be storing information and transmitting it to other generations of molecules, which would start replicating themselves without the help of the clay.

We, in the 21st century, are not used to scaring lightning and thunder; but billions of years ago Mother Earth was bombarded by meteorites and lightning continuously. Thousands of volcanoes were spurting kilometers of hot, sulphur-loaded lava into the atmosphere, carrying with them hydrogen, ammonia, methane and other molecules into the air. All these exposed to the dense lightning spark and ground water could have been enough to kickstart the formation of complex organic molecules that, billions of years later, would give life to the blue planet. Could all this have occurred on a grander scale on our planet? Or is it still scientific speculation?

The jury has been out for quite some time now. When will it be back?

Readers may wish to consult Wikipedia – https://en.wikipedia.org/wiki/Abiogenesis – cite_note-69 – for further reading on this subject.

* Published in print edition on 24 June 2016

Add a Comment

Your email address will not be published.

Solution by Web Vision Ltd