The most fundamental and least-aware topic is the origin of life. Many researchers worked on it and analyzed the origin of life and created segregated hypotheses into four categories.
Hypothesis 1 explains the traditional concepts of theology and physiology. It does not have any scientific knowledge, but it explains the biblical accounts. Also, it simply explains the organic molecules like amino acids and nucleotides, which were formed first of all life on earth.
Hypothesis 2 does not support the spontaneous growth of animals from putrefying matters. During the 17th century, the British physiologist William Harvey studied the reproduction and development of deer and its group. And discovered that every animal comes from an egg. Francesco Redi, an Italian biologist established the theory in the 17th century that the maggots in meat came from flies’ eggs and deposited on the meat. In the 18th century, Lazzaro Spallanzani, an Italian priest explained that sperms are necessary to fertilize eggs in mammals. This was proven that the large animals are not developed spontaneously, but developed from the fertilized eggs. But still, many hope that the smaller beings, microorganisms, are spontaneously developed from debris. To prevent maggots, they start covering meat with a fly proof screen. Although the spontaneous generation study remains controversial between French bactériologistes Louis Pasteur and Félix-Archimède Pouchet after researching the fertilization of grape juice. Pasteur said it should be because of microbes in underground air. But, Pouchet argued about how life comes spontaneously from non-living organisms. As a result, they concluded that life does not occur spontaneously from nonliving matters.
In the late 19th century, American historian James Strick reviewed the controversies and supported the life of non-lives. The origin of life on earth was discussed by many scientists that the microorganisms can come from preexisting lives through cell inhibition.
Hypothesis 3 started to be built at the end of the 19th century by the Swedish chemist Svante A. Arrhenius. He suggested that life arose from ‘panspermia’. It is the microscopic spores that wafted by radiation pressure through space from planet to planet or solar system to solar system. This idea avoids the problem of finding the beginning of life on earth but never resolved. It raises the question, is it possible to transport to earth over interplanetary? How interstellar distance, vacuum, and radiation allow it?
Hypothesis 4 is providing some clear solutions regarding the first cell on earth. T.H. Huxley, a British biologist wrote the book ‘Protoplasm: The physical Basis Of Life’ and John Tyndall, a British physicist wrote the book “Belfast Address”. They both asserted that life could develop from inorganic chemicals. Later, researchers found that urea, and other organic molecules have continued their development from inorganic chemicals. In 1828, the term ‘organic’ was named as ‘from life’, which means it does not require biological origin. It can maintain its metabolism, growth, and reproduction.
Darwin’s attitude relates the origin and evolution of the earth with thermonuclear reactions. This was either in stellar interiors or supernova explosions. It generates all the chemical elements in the periodic table with massive hydrogen and helium. Supernova explosions and stellar winds distribute the elements into the interstellar medium, which is generated to form stars and planets. As the thermonuclear processes are well-documented, they are more probable than others. The facts deal with the idea of the certain cosmic distribution of the major elements in the universe. Some biological atoms interact with numerical abundances in the universe and on earth. The composition of life always lies between the average composition of the universe and the Earth. 99% of the life in the universe and the earth is made of Hydrogen, Helium, Carbon, Nitrogen, Oxygen, and Neon.
Even though the elemental composition varies from place to place in the universe, these comparisons are general. 0% mentioned here stands for any quantity less than 10–6 percent.
The Jovian planets like Jupiter, Saturn, Uranus, and Neptune are closer to cosmic composition while compared to earth. They have large gaseous components formed by cosmic components with little water, and the upper atmosphere of these planets are cold as they are far away from the Sun.
The Earth and other planets in the solar system are less massive and have a hotter upper atmosphere. Even today, hydrogen and helium are escaping from Earth’s atmosphere. It may be noted at a higher rate during the earth formation. Early earth does not contain CO2, O2, and N2. It was in the form of atoms and now they are saturated. Likewise, methane, ammonia, and water are reduced to minerals like Uraninite and Pyrite. These sediments were formed billions of years ago and settled in atmospheric conditions. In 1920, the British geneticist J.B.S. Haldane and Russian biochemist Aleksandr Oparin showed that the non-biological component can develop organic molecules in the presence of Oxygen-rich components in the atmosphere. The presence of 21% of oxygen in the atmosphere produces cyanobacterial, algal, and plant photosynthesis. The organic matter spontaneously produces prior to the origin and evolution of the earth.
During the alkaline conditions, the presence of inorganic catalyst formaldehyde spontaneously reacts to form a variety of sugars. The fundamental to form five-carbon sugars are nucleic acids and six-carbon sugars like glucose and fructose can be easily developed. This is a common metabolite and structural building block in life. The nucleotide bases and biological pigments are called porphyrins. The presence of suitable protein, carbohydrates, and amino acids can give organic molecules on the earth.
Q1. What is the Best Theory That Explains the Origin of Life?
Ans. The RNA world is a prevailing best theory to explain the origin of life on earth. It was published in 1980. It explains the evolution of a self-replicating catalytic molecule, which is a signature capability of living organisms. But it does not explain the proto biological molecule development.
Q2. What is the 4 Stage Hypothesis for the Origin of Life?
Ans. The hypothesis for the beginning of life on earth is of 4 stages. The first stage was formed with precursors of life, like amino acids and nucleotides. The second stage of the hypothesis explains the synthesis of complex molecules such as nucleic acids and proteins. The third stage of the hypothesis explains the cell structure formation, which is enclosed by membranous structures. And the fourth stage of the hypothesis explains the cell characteristics, this membranous structure emerged as more chemically selective and developed unique properties.