ORIGIN OF LIFE
How did life originate? This question has perplexed scientists and philosophers throughout human history. There was a time when it was believed that life arose spontaneously from nonliving matter. It was thought that fish and frogs were produced from mud, maggots arose from decaying meat, insects were formed from plant juices and that micro-organisms arose spontaneously from air or water. It was the great French microbiologist Louis Pasteur who finally disposed such theories of ‘spontaneous generation’ and demonstrated once and for all that life originates only from pre-existing life.
SCIENTIFIC HYPOTHESIS FOR ORIGIN OF LIFE
How then did life originate in the first place? Charles Darwin in a letter to his friend and distinguished botanist Sir Joseph Hooker provided a clue to this puzzle when he wrote “if (and oh, what a pit if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts, heat electricity etc., present that a protein compound was chemically formed, needy to undergo still more complex changes at the present day such matter could be instantly devoured, or observed, which would not have been the case before living creatures were formed” The idea that life could have originated on the primordial earth even though it might not today, because the conditions on the primordial earth were rather different from those that we see today, has since become the basis of the most widely accepted scientific theory of the origin of life. A detailed theory based on this idea was proposed in the year 1923 by the Russian biochemist A.J. Oparin and in 1928 independently one of the most outstanding biochemist of our time J.R S. Haldane.
The Primitive Earth
There is evidence that the earth was formed about 4600 million years ago. The earth and other planets and the sun, too are believed to have been formed by the condensation of clouds of cosmic dust and gas. At the time of its formation, the earth was so hot that everything in it was probably in gaseous form. As the earth began to cool, its matter began to condense so that solids, liquids as well as gases could co-exist. Recent studies suggest that simple one celled organism. Somewhat similar to today’s cyanobacteria, were present in the earth about 3600 million years ago. This finding suggests that life originated sometime between 4600 and 3600 million years ago.
Conditions on the primordial earth
About 3600 million years ago conditions were strikingly different from those found today. The earth’s atmosphere at that time was reducing and not oxidizing as it is today. You would recall that large quantities of hydrogen, nitrogen, water vapour, carbon dioxide, lipids and amino acid were present on the primitive earth but free oxygen is unlikely to have been present in any significant amounts. The Oparin Haldane theory suggests that complex organic molecules would have been formed through a series of chemical reactions in the earth’s “primordial soup” or we might say Darwin’s warm little pound. The theory also reasoned that make available in the form of heat cosmic rays and lighting to drive these chemical reactions.
(Note: Copyright :Dr. Ajeet Jaiswal, Pondicherry University, India)