DEFINITION OF LIFE: All groups of living organisms share several key characteristics or functions: order, sensitivity or response to stimuli, reproduction, adaptation, growth and development, regulation, homeostasis, and energy processing. When viewed together, these characteristics serve to define life.
Life abounds on earth in many forms. But what is life? Firstly, the origin of life on earth is one of the greatest mysteries of science. Are we alone in the universe? May or may not be, but we cannot give a definitive answer to that question.
Logically, we presume that since life evolved on Earth due to certain conditions, it should also evolve on other planets orbiting other stars in the Universe where similar conditions are present. But to date, we do not even know how life came about on Earth.
The Stanley Miller experiment proves that amino acids evolved on the primordial earth, but it does not say how those amino acids combined to form the varieties of life around us. A lot has to be understood yet about life and we need to solve that mystery to say something with certainty.
The earth is about 4.5 billion years old. Scientists estimate that 200 million years after, that is about 4.3 billion years ago life evolved on earth. The oldest known fossils on the earth are however only 3.7 billion years old. That leaves a 600 million-year window for which we do not have any information.
During this time it is possible that life may have evolved but has been repeatedly extinguished by catastrophic collisions with asteroids and comets. However, we have not found any evidence for that so far.
Life is supposed to have first begun in volcanically active hydrothermal environments on land and at sea. Some microorganisms thrive in the scalding highly acidic hot springs environments like those found today in Norway and Yellowstone in the USA. Therefore such organism may have formed on planets with similar environments in other parts of the Universe.
However, this is merely a hypothesis without any supporting proof. This is the problem with life, as we do not know how inanimate became animate; it becomes very difficult to say if it exists on other planets.
What are in the ingredients for life on Earth?
It requires a steady energy source like the Sun, organic compounds and water. There are some elements that are crucial for life. They are Carbon, Hydrogen, Oxygen, Nitrogen and Phosphorous.
Now a planet so close to the Sun cannot actually have Carbon and Nitrogen. Both the elements become solid only under very cold temperatures that are not present on Earth. Carbon is rare at the earth’s surface and chemically bonds more with iron than rock. So how did the Carbon found on the earth’s surface get there?
Water now covers about 70% of the Earth’s surface but how much of it was there 4 billion years ago for life to evolve?
How did life emerge on Earth?
Scientists believe that life emerged from a Primordial soup. In 1952 as a University of Chicago graduate student Stanley Miller performed his famous experiment along with Harold Urey, a Nobel winner in Chemistry.
They injected Methane, Ammonia, and water vapor into an enclosed glass container to simulate lightning. Amino acids, the building blocks of Proteins soon formed in the container. They realized that this process would have created the way for the formation of life.
Scientists now believe that Earth's early conditions had a different chemical makeup from the one used by Miller in their experiment. The experiment gave rise to a new scientific field named prebiotic or abiotic Chemistry.
Some scientists think that molecules for life may have been produced outside the Earth and were brought to Earth by meteorites or comets. In 1969 the Murchison meteorite that fell in Australia contained dozens of different amino acids.
In 2019, a team of researchers in France and Italy reported finding extra-terrestrial organic material preserved in the 3.3 billion old sediments of Barberton, South Africa. They suggested micro meteorites as the likely source. Further evidence came in 2022 from the samples of the Asteroid Ryugu brought back by a Japanese mission. It had over 20 different amino acids.
Chirality means mirror image, non-superimposable molecules. An experiment in 1953 pointed out that without Chirality, large biological molecules like proteins would be unable to form structures that could be reproduced.
But how can inanimate matter combine in a certain way to develop to be a composite organism in the first place, where each part becomes special for a particular job? It is very easy to say that some chemical reaction produced Amino acids as the Miller experiment has shown but, then how do those amino acids combine and formed the DNA, RNA and Proteins?
Is it not silly to say that they evolved? How did that happen? Again taking for granted that proteins and RNA and DNA have formed, how did they conveniently combine to make complex organisms?
The problem here is that there are too many questions without any answers unless we exercise our sheer imagination which is not based on any proof.
The Soviet Biochemist A I Oparin has advanced his theory for evolution of life. In it he says
1. There is no fundamental difference between a living organism and lifeless matter. The complex combination of manifestations and properties characteristic of life must have arisen as a part of the process of the evolution of matter.
2. Taking into account the then-recent discovery of methane in the atmospheres of Jupiter and the other giant planets, Oparin suggested that the infant Earth had possessed a strongly reducing atmosphere, containing methane, ammonia, hydrogen , and water vapor. In his opinion, these were the raw materials for the evolution of life.
3. In Oparin's formulation, there were first only simple solutions of organic matter, the behaviour of which was governed by the properties of their component atoms and the arrangement of these atoms into a molecular structure.
Gradually though, he said, the resulting growth and increased complexity of molecules brought new properties into being and a new colloidal-chemical order developed as a successor to more simple relationships between and among organic chemicals. These newer properties were determined by the interactions of these more complex molecules.
4. Oparin posited that this process brought biological orderliness into prominence. According to Oparin, competition, speed of cell growth, survival of the fittest, struggle for existence, and, finally, natural selection determined the form of material organization characteristic of modern-day living things.
Even the simplest of unicellular organisms have a complexity of structure and function that staggers the mind and is removed from the beginnings of life by a genealogy extending for millions and millions of years.
Pasteur’s unequivocal experiments have given us irrefutable proof that living organisms, no matter how simple they might be, cannot be generated from organic matter. Yet this might have happened in the millions and millions of years of evolution. It is impossible by any experiments to prove Biogenesis but looking to the life around us it looks like a reasonably consistent logical necessity.
The conditions on the earth in the last 2 billion years have undergone radical alterations and perhaps Biogenesis may not be possible in the current conditions. Even if it does evolve, the innumerable predatory organisms that exist on the earth would quickly destroy any such new organism.
So, is life a new property of Organic matter acquired in the course of evolution or is it something that resulted from the organization of organic matter?
There is every reason to believe that a certain period of Earth’s history must have been completely sterile. Proteins containing Nucleic acids are the only constituents of the organisms that grow and reproduce by self-duplication or by replication. Neither viruses nor genes can duplicate or replicate themselves unless implanted in a cell or nucleus. So are these Nucleo proteins living or non-living?
Till Louis Pasteur conducted his brilliant experiments which were published in 1862, most scientists believed that microorganisms automatically got generated from matter. Pasteur conclusively proved that in every case the growth of the organism is due to contamination and there is no fresh generation of anything.
There are two fundamental theories based on the conception of continuity of life. 1. The theory of Cosmozoa along with the closely related theory of Panspermia and 2. Preyers theory of eternity of life.
Preyer starts from the empirical theory that all organisms are derived from similar other organisms, and questions “Is not the problem of the origin of life based on a wrong assumption that the living must have come sometime from the non-living? “Why not consider the living to be in eternal existence like other inorganic matter?”
But if a living thing has only come from a living substance then that substance must have also existed at the time when earth was still a molten mass. Preyer insists that the living did exist in that molten mass. He says “If we rid ourselves of the idea wholly arbitrary and unsupported by facts that Protoplasm can exist only in its current composition, and of the old convenient prejudice that at first there was only inorganic substance, we can without fear take the next bold step, discard altogether all belief in a primary origin, and recognize the timelessness of the current of life. “
