Origin of Life: The Timeline of
Theories
Looking at the series of theories and events contributing to OUR origin, the very first happening that occurred was The Big Bang which took place about 13.7 billion years ago. It is the leading explanation about the beginning of the Universe. It talks about the universe as we know it starting with a small singularity, then expanding over these billions of years to the cosmos that we know today. Cosmos refers to the universe seen as a well-ordered whole; it is what we call the ‘Brahmanda’ in Hindi. Our solar system formed about 4.6 billion years ago. The atmosphere was highly reducing. At that time, earth was not ready to bear life, not at least the type that we see today. The reason I mentioned this statement is that it was assumed that before the existence of the precursors of the modern life forms, several other life forms did exist which, due to the changes in the conditions of the environment, could not sustain. Oxygen began accumulating in the atmosphere about 2.7 billion years ago.
Aristotle (384-322 BC) put forth the ideas of ‘Spontaneous Generation’ of life, which were widely believed for centuries. Clearly, it assumed the birth of life from abiotic i.e. non-living origin. Jan Baptista van Helmont (1580-1644) even gave the ‘recipe for mice’ in which he claimed to produce mice within 21 days, by putting a soiled shirt and grains of wheat in an open jar and letting it ferment. Of course, he could not provide any experimental evidence for the same. Later, the recipes for frogs, flies, bees and scorpions etc. also came up. In 1828, Friedrich Wohler gave the theory that organic and non-living compounds are different and showed the formation of urea (an organic compound) from ammonium cyanate (an inorganic/ non-living compound) by heating the latter. In 1859, Louis Pasteur showed that there is no such thing as spontaneous generation of the life, and that life can only arise biotically from other living systems. This may seem obvious now but it was a major concern at that time.
At some point of time, the ‘Theory of Panspermia’ prevailed, whose first known mention was in the writings of the Greek philosopher Anaxagoras (500-428 BC). It was the theory that life on the Earth originated from microorganisms or chemical precursors of life present in outer space which were able to initiate life on reaching a suitable environment. The concept of Exogenesis from Mars to Earth is still unresolved. Although a meteorite from Mars recovered in 1984 was claimed to contain fossil life but this is disputed. It is thought that Mars may have been habitable billions of years before Earth. Also, radio astronomy found the evidence of organic molecules on space dust. The collisions of comets with primitive Earth may have transferred the organic molecules from space to here. The Murchison meteorite in Australia in 1969 contained organic molecules.
Aleksander Oparin in 1924 and J.B.S. Haldane in 1929 gave hypothesis separately that putative conditions on the primitive Earth favoured the chemical reactions to synthesise more complex organic compounds from simple inorganic precursors. Sunlight reacted with non-living chemicals in the ‘primeval soup’. The ‘primeval soup’ or the ‘primordial soup’ was a mixture of water, carbon dioxide and ammonia and all sorts of phosphoric salts, light, heat, electricity, etc. in the primitive oceans of the Earth. In 1953, two scientists Harold Urey (1893-1981) and Stanley Miller (1930-2007) conducted an experiment together, known as Urey- Miller experiment and confirmed the hypothesis. In the experiment, they simulated the conditions of the early Earth, such as the reducing environment, used electrodes to simulate lightning, and tested the chemical origin of life under those conditions. After some days it was observed that the flask contained compounds like amino acids, hydroxy acids and other organic compounds.
But there remained a larger question as to the nature of the origin of genetic materials- RNA and DNA. RNA is thought to be the first hereditary material. Even today, some organisms such as viruses use RNA to store genetic information, but usually, the information is stored in DNA. It is thought that RNA based life predated DNA based life and that that RNA eventually evolved into DNA.
The most accepted theory is as follows:The key stages leading to ‘life’ would be the origin of biological monomers, polymerisation of these monomers and evolution of the polymers into cells.
The precursors of early life are known as Protobionts. These were the aggregates of organic molecules, surrounded by a membrane, that abiotically coalesce into resemblances of living matter and are thought to be the precursors of the prokaryotic cells. Protobionts form spontaneously in lab experiments from mixtures of organic molecules. They contained RNA that codes for metabolic proteins. These protobionts absorbed food and the proteins catalyze it to make energy which can be used for growth and division to daughter cells. Natural selection would favor protobionts that grow and replicate. ‘Natural selection’ is the process whereby organisms better adapted to their environment tend to survive and reproduce. When the organic molecules in the earth’s water bodies were gone, the protobionts would “evolve” to either obtain energy by photosynthesis or predation. It would only take the creation and evolution of one protobiont to give rise to the all the different organisms we see today.
Marcus Garvey says,
“A people without the knowledge of their past history, origin and culture is like a tree without roots.”
True indeed. We still have a long way to go
Theories
By YASHNA KHAKRE
“Many investigators feel uneasy stating in public that the origin of life is a mystery, even though behind closed doors they admit they are baffled.”
These are the words of Paul Davies in his book ‘The Fifth Miracle: The Search for the Origin and Meaning of Life’. ‘The Origin of Life’ is the biggest scientific mystery which is yet to be solved. As a science student, I do not feel that this is something that only the people related to the disciplines of sciences must know. The focus here would not just be on the origin of human race as such, but the origin of entire “living life” as a whole.
In the first few lectures of our biology course, we were taught about the origin of life. Doesn’t it sound unconvincing that the human race which has come a long way, as far as the scientific and technological advances are concerned, is yet to know their birth? One of the reasons is that the ideas are many, but the facts are only few. The oldest fossils of the microorganisms known by the scientists were that of 3.5-3.7 billion years ago, which were claimed to be embedded in Western Australia. But in a recent discovery by Australian scientists, the “Stromatolite” fossil has been uncovered in remote Greenland by a team led by University of Wollongong researcher Allen Nutman. This discovery also suggests the possibility of life on other planets.
“Many investigators feel uneasy stating in public that the origin of life is a mystery, even though behind closed doors they admit they are baffled.”
These are the words of Paul Davies in his book ‘The Fifth Miracle: The Search for the Origin and Meaning of Life’. ‘The Origin of Life’ is the biggest scientific mystery which is yet to be solved. As a science student, I do not feel that this is something that only the people related to the disciplines of sciences must know. The focus here would not just be on the origin of human race as such, but the origin of entire “living life” as a whole.
In the first few lectures of our biology course, we were taught about the origin of life. Doesn’t it sound unconvincing that the human race which has come a long way, as far as the scientific and technological advances are concerned, is yet to know their birth? One of the reasons is that the ideas are many, but the facts are only few. The oldest fossils of the microorganisms known by the scientists were that of 3.5-3.7 billion years ago, which were claimed to be embedded in Western Australia. But in a recent discovery by Australian scientists, the “Stromatolite” fossil has been uncovered in remote Greenland by a team led by University of Wollongong researcher Allen Nutman. This discovery also suggests the possibility of life on other planets.
Aristotle (384-322 BC) put forth the ideas of ‘Spontaneous Generation’ of life, which were widely believed for centuries. Clearly, it assumed the birth of life from abiotic i.e. non-living origin. Jan Baptista van Helmont (1580-1644) even gave the ‘recipe for mice’ in which he claimed to produce mice within 21 days, by putting a soiled shirt and grains of wheat in an open jar and letting it ferment. Of course, he could not provide any experimental evidence for the same. Later, the recipes for frogs, flies, bees and scorpions etc. also came up. In 1828, Friedrich Wohler gave the theory that organic and non-living compounds are different and showed the formation of urea (an organic compound) from ammonium cyanate (an inorganic/ non-living compound) by heating the latter. In 1859, Louis Pasteur showed that there is no such thing as spontaneous generation of the life, and that life can only arise biotically from other living systems. This may seem obvious now but it was a major concern at that time.
At some point of time, the ‘Theory of Panspermia’ prevailed, whose first known mention was in the writings of the Greek philosopher Anaxagoras (500-428 BC). It was the theory that life on the Earth originated from microorganisms or chemical precursors of life present in outer space which were able to initiate life on reaching a suitable environment. The concept of Exogenesis from Mars to Earth is still unresolved. Although a meteorite from Mars recovered in 1984 was claimed to contain fossil life but this is disputed. It is thought that Mars may have been habitable billions of years before Earth. Also, radio astronomy found the evidence of organic molecules on space dust. The collisions of comets with primitive Earth may have transferred the organic molecules from space to here. The Murchison meteorite in Australia in 1969 contained organic molecules.
But there remained a larger question as to the nature of the origin of genetic materials- RNA and DNA. RNA is thought to be the first hereditary material. Even today, some organisms such as viruses use RNA to store genetic information, but usually, the information is stored in DNA. It is thought that RNA based life predated DNA based life and that that RNA eventually evolved into DNA.
The most accepted theory is as follows:The key stages leading to ‘life’ would be the origin of biological monomers, polymerisation of these monomers and evolution of the polymers into cells.
The precursors of early life are known as Protobionts. These were the aggregates of organic molecules, surrounded by a membrane, that abiotically coalesce into resemblances of living matter and are thought to be the precursors of the prokaryotic cells. Protobionts form spontaneously in lab experiments from mixtures of organic molecules. They contained RNA that codes for metabolic proteins. These protobionts absorbed food and the proteins catalyze it to make energy which can be used for growth and division to daughter cells. Natural selection would favor protobionts that grow and replicate. ‘Natural selection’ is the process whereby organisms better adapted to their environment tend to survive and reproduce. When the organic molecules in the earth’s water bodies were gone, the protobionts would “evolve” to either obtain energy by photosynthesis or predation. It would only take the creation and evolution of one protobiont to give rise to the all the different organisms we see today.
Marcus Garvey says,
“A people without the knowledge of their past history, origin and culture is like a tree without roots.”
True indeed. We still have a long way to go
Great concept and conclusion impressed with your work
ReplyDeleteGood..
ReplyDeleteclearly elaborated concepts ...yet the mystery remains unclear regarding first genetic material formed
ReplyDelete