Origin of Life on Planet Earth!
Darwin explained the evolution of life from simple to complex forms. Mendel tried to explain the inheritance of traits in living beings.
But we are still trying to explain the origin of life on the earth. We can speculate whether life began as a cell or from an inorganic molecule.
Probably some of the chemical reactions involved in metabolism began when no form of life existed.
Small carbon-containing molecules such as acetic acid and citric acid may have been abundant on the young earth. They took part in chemical reactions that produced larger molecules like amino acids, lipids, sugars and RNA. Gradually, these molecules may have interacted and produced the biomolecules essential for life.
The above account of the origin of life is based on the general concepts outlined by Aleksandr Ivanovich Oparin (1924), John Burdon Sanderson Haldane (1928), Stanley Lloyd Miller and Harold Clayton Urey (1953), and Sidney Walter Fox (1965).
They believed that life arose on the early earth some 3.5 billion years ago by a series of chemical reactions in the seas. The conditions on the early earth were different from those of the present. Elements such as carbon and nitrogen were not present as their oxides (e.g., CO2 and NO2), as they are today, but were present as CH4 (methane) and NH 3 (ammonia).
Oxygen was not available as there were no photosynthesizing organisms. Hence the atmosphere was a reducing (electron-adding) one and the synthesis of organic molecules could occur easily.
In their experiments, Miller and Urey simulated the prebiotic conditions (that is, when there was no life on the earth) and produced some amino acids (units of proteins) and other organic compounds. Their experiments suggested how these organic molecules were produced on the early earth.
In these experiments, a mixture of methane, ammonia, water vapour and hydrogen was circulated through water at a temperature just below 100°C, and sparks were passed through the gaseous mixture to simulate the lightning flashes on the early earth.
After several days of experimentation, the colour of the solution changed. The analysis of the liquid showed the presence of simple carbon compounds like several types of amino acids that make up protein molecules essential for life.
However, when the experiment was carried out in oxidizing conditions, no amino acids were formed. This suggested that reducing conditions were essential for any prebiotic synthesis of organic molecules. Therefore, we can assume that life cannot arise again on the earth because the reducing atmosphere that was conducive to the formation of biomolecules is no longer present.
The life forms present today are diverse. They have been changing and evolving since the time they originated. Let us learn how new species originated from existing ones.