What is the definition of life given by
Biologists? Life is a self-sustaining chemical system capable of Darwinian
Evolution.
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 of 1953 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 anything 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. As mentioned earlier, in 1953 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 vapour 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.
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 form 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 would not be 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 which requires life to form 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
an atmosphere containing methane, ammonia, hydrogen , and water vapour. 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. Gradually
though, he said, the resulting growth and increased complexity of molecules
brought new properties into being and a new set of organic chemicals.
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. Today if life is not already
present, 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 (which says
that life originated elsewhere in the Universe and later came to earth) along with the closely related theory of
Panspermia( that seeds of life exist in all the Universe and even in empty
space)
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. “
So, theories may abound but we actually
have no means of proving which is correct, and at the most they are mere
conjectures till proven otherwise and life remains a mystery to us
