Origin of Life and its Theories

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Origin of Life :-

It is the natural process by which life has arisen from nonliving matter such as inorganic compounds.

The life originated in the primitive Ocean on the Earth.

  • Earth belongs to the Solar system of Milky Way Galaxy of universe and Cosmos. It originated from the Sun about 4.5 to 5 billion years ago, the temperature was very high ( about 5000⁰C ).

As the distance from Sun increased, cooling process started. it resulted into the differentiation of regions –

Fig. 1. Regions of primitive Earth

1. Crust :-

It is a outermost solid part and present in the form of large tectonic plates. It is mainly composed of Silica and Aluminium.

2. Mantle :-

it is the middle hot and fluid region mainly composed of silica and Manganese.

3. Core :-

it is the innermost or centrally hot and gaseous region mainly, composed of Fe, Nickel. During differentiation of their region the heavier metals were concentrated in the Central part.

  • The Earth was surrounded mainly by H⁺ which combined with O²⁻ to form water vapor. During the formation of Crust, a series of volcanic eruption take place, releasing the magma or lava. which contain mainly Nitrite and Carbide.
  • Hydrogen ions combine with the Nitrite to form Ammonia and with Carbide to form Methane. Therefore the first or primordial atmosphere develop around the primitive Earth. Primordial atmosphere mainly contains H⁺, Water vapor, Ammonia and Methane.
  • The condensation of water vapor, resulted into the development of the first or primordial fossil which was later term as hot nutrient soup by Haldane. The whole land mass was submerged.

Theories about Origin of life :-

1. Special Creation Theory :-

It was proposed by Hebreus, mentioned in Bible and supported by father Suarez. According to this Theory life is originated from God.

This theory about Origin of life was strongly objected by Darwin. It is now discarded.

2. Cosmozoic theory or Theory of Panspermia or Interplanetary Theory :-

it was proposed by Ritcher and Helmhotz. According to this Theory, the origin of life panspermia come to the Earth along with meteorites from other planets. They evolved into different species of Flora and Fauna in the suitable condition. It is now discarded.

3. Spontaneous Generation Theory or Theory of a Biogenesis :-

Biogenesis theory about Origin of life were proposed by Aristotle, and Arrhenius. It was strongly supported by Leeuwenhoek ( microbiologist ), Willium Harvey ( phisiologist ), Von Baer ( father of embryology ), Buffon, John Needham, Priestley.

According to this Theory life has originated spontaneous from non-living substances.

  • This Theory was first objected by Francesco Redi and then Lazaro Spallanzant.
Fig.2. Redi’s Experiment

Redi and Spallanzant experiment were discarded by Buffon and Needham with the support of Leeuwenhoek and Priestley.

  • Finally Louis Pasteur performed a classic experiment, popularly known as pasteurisation, which becomes the final death to the Spontaneous Generation Theory.

4. Materialistic Theory :-

Proposed by Oparin ( Russian biochemist ) in his book named origin of life on earth.

According to Oparin the constituents of primordial atmosphere ( hydrogen ions, water vapor, ammonia and methane ) were subjected to very complex chemical reaction for thousands of years in the presence of catalyst ( heat release during lightning and the solar radiation ). these reactions resulted into the formation of small coloidal molecule surrounded by thin water whithin the primordial ocean.

  • These molecules were termed as microspores by Sydney Fox. These molecules were finally combine to form large molecules named Coacervates by oparin.
  • Coacervates were first biomolecules with the synthesis of nucleic acid and Coacervates transform into pre-cells or proto-cells, with the development of cell wall the pre-cell transformed into prokaryote.
  • The first prokaryote evolved was Eubacteria then evolved Archebacteria ( about 3.5 billion years ago ).
  • Finally, Cyanobacteria evolved about 1 billion years ago.
  • According to Haldane, a British physiologist with Indian citizenship, the Cyanobacteria synthesised chlorophyll and performs photosynthesis, changing the atmosphere from reducing to oxidising in nature. The formation of oxidising and origin of life were stoped in the medium.

Therefore Materialistic Theory is also known as Oparin – Haldane’s Theory.

Miller – Urey experiment ( 1953 ) :-

Miller Uray
Fig. 4. Miller’s Experiment

Stanley Miller and Harald Urey ( British Physiologist ) formed a reducing sparks apparatus inside which a mixture of hydrogen ions, water vapor, ammonia and methane was heated for about 7 days. After cooling the apparatus, the small protein molecules called proteinoids were obtained, these proteinoids by partial dehydration combined to form large Coacervates.

Miller – Urey experiment established Oparin – Haldane’s Theory about Origin of life

  • Sydney Fox and Dose heated the mixture of water and amino acids upon an igneous rock within an hour, open to produced the proteinoid, nucleotide . Finally established life has originated on the Earth from both inorganic and organic materials in reducing medium.

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