Origin of Life on Earth According To Science

Study of the Miller-Urey experiment.

Origin of life on earth

Man has always wondered how he came into existence, who created him, and why he was created. Questions of such nature have been asked throughout human history. Every ancient thinker, philosopher or prophet, has tried to give some answer to this question and suggest some mechanism for the birth of life.

Man is but a small part of life. In reality, there is a vast variety of creatures lingering around us. How did they come into existence? Are we related to them in any manner whatsoever? This article proposes to take you back to a distant past when there was no life on our planet and helps you imagine how life could have originated on it.


Panspermia


According to an ancient Greek idea, life exists throughout the universe. It is distributed to different planets in small units through space dust, meteoroids, asteroids or comets. It was assumed that under favourable conditions of temperature and moisture, these units of life would come alive and give birth to the initial living beings.

origin of life on earth
Panspermia

Panspermia was first mentioned in the writings of the 5th century BC Greek philosopher Anaxagoras. Despite being old, the idea is quite witty, isn't it? It has assumed a more scientific form in the recent years thanks to the contributions of astronomers Fred Hoyle and Chandra Wickramasinghe.

It is a very well known fact that the cosmic dust is present throughout space. Hoyle and Wickramasinghe proposed in 1974 the hypothesis that some dust in the interstellar space was largely organic, which Wickramasinghe later proved to be correct.

But Panspermia assumes that there is a universal storehouse of life throughout space and thus indeed avoids answering the question as to how life anywhere originated in the first place.

Divine Creation


One belief, common among the people of all cultures, is that all the different forms of life including human beings were suddenly created by a divine order about 10,000 years ago. These large number of creatures have always been the same and will last without change from one generation to another, until the end of the world.

Such a theory of creation is unreasonable because fossils of plants and animals suggest that life is of much older origin. In fact, some researches show that life on Earth existed even 3.5 billion years ago. There are very many reasons why this particular idea is untrue. It is therefore surprising as to why people may still hold on to this belief system.

Spontaneous Generation


The theory known as spontaneous generation held that complex, living organisms could come into existence from inanimate objects. Mice might spontaneously appear in stored grain or maggots could spontaneously appear in meat. It was synthesized by the Greek philosopher and biologist Aristotle.

Aristotle

According to Aristotle, animals and plants come into existence in earth and in liquid because there is water in earth, and air in water, and in all air is vital heat so that in a sense all things are full of soul. Therefore, living things form quickly whenever this air and vital heat are enclosed in anything.

Aristotle's influence was so large and powerful that his construct of spontaneous generation remained unchallenged for more than two thousand years. According to Aristotle it was a readily observable truth. But, in 1668, Italian biologist Franceso Redi proved that no maggots appeared in meat when flies were prevented from laying eggs.

origin of life on earth
There is no spontaneous generation

Spontaneous generation is no longer debatable among biologists. By the middle of the 19th century, experiments by Louis Pasteur and others refuted the traditional theory of spontaneous generation and supported biogenesis, the idea that only life begets life.


Chemical Evolution


The life as we know it is based on carbon containing molecules. Therefore, Soviet biochemist, Oparin, and British biologist, Haldane, proposed that life could have arisen from simple organic molecules. In other words, to understand the origin of life, one must have a knowledge of the organic molecules on earth.

The early Earth was a hot ball of fire. Sources of energy such as cosmic rays, UV radiation, electrical discharges from lightning and heat from volcanoes, were readily available. Therefore, the earth acted like a big factory producing thousands of compounds a day. This was a state of agitation.

early earth with warm waters

In these severe conditions, oxygen, could not remain as free oxygen. It was combined with other elements in compounds such as Water and Limestone. Compounds of carbon and hydrogen, such as methane, were also formed. Nitrogen and hydrogen combined to form ammonia. These compounds are today called organic compounds.

With the passage of time, the earth had started cooling down. As it cooled sufficiently, prolonged rains were caused due to condensation of steam. The rains began accumulating in the depressions on the earth and so the oceans were formed. The water was warm and soup-like containing various kinds of organic molecules in abundance.

organic molecules

Interaction between these compounds in the warm waters resulted in the formation of yet more compounds, which among other things also contained amino acids having a composition of carbon, hydrogen, nitrogen and oxygen. These amino acids combined with one another in large numbers to form proteins, which are the building blocks of life.


Miller-Urey Experiment


In discussing events which must have happened billions of years ago, there is a certain amount of guess work and uncertainty involved. But the reasoning has to conform to a good deal of available evidence as well as to the basic laws of physical sciences.

The above idea could be tested by recreating the proposed conditions of the early earth in a laboratory.

In the year 1952, American biochemists Stanley Miller and Harold Urey did exactly the same thing but on a very small scale. They subjected a gaseous mixture of methane, ammonia, water vapour and hydrogen in a closed flask at 80 degree Celsius to electric sparking, for a week.

origin of life on earth

When examined a week later, the arrangement was found to have formed simple amino acids in the bottom, which are essential for the formation of proteins. Miller and Urey had shown that several organic compounds could be formed spontaneously by simulating the conditions of earth's early atmosphere, as hypothesized by Oparin and Haldane.

Elements of life, produced by man, in laboratory.

The scientific community worldwide was largely impressed by this accomplishment. In fact, three years after the success of Miller's experiment, American physicist Richard Feynman wrote a poem, titled, an atom in the universe, celebrating man's knowledge of the origin of life on earth.


Miller continued his research until his death in 2007. He not only succeeded in synthesising more and more varieties of amino acids, but also produced a wide variety of inorganic and organic compounds vital for cellular construction and metabolism. We salute the efforts of such a scientist who devoted his life studying the most important question known to man.

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