Name: Common Misconceptions About Evolution
Uploaded: 2019-07-19
Duration: 6 min 20 s
Description: Evolution is particularly vulnerable to misunderstandings around the scientific language. Let's find out the common misconception about evolution.

Question

Describe Oparin - Haldane theory of chemical origin of life.

Accepted Answer

The 'Theory of chemical evolution of life' was proposed by a Russian scientist Alexander Ivanovich Oparin (1924) and British scientist J.B.S. Haldane (1929). This theory suggests that, around three billion years ago, life originated from non-living matter, in a primitive atmosphere, through a process of chemical evolution. The process of chemical evolution can be divided into the following steps:

1. Origin of earth and its primitive atmosphere:

Evidence suggests that earth originated about 4.6 billion years ago.

When it was split from the sun, it was a glowing ball of fire and a rotating cloud of hot gases, vapours of various elements and pieces of rocks and metals called nebulous. This mass of gas exploded with a Big Bang into several small pieces.

As the earth moved away from the sun, it started cooling down. This led to the condensation of gases.

The heavy elements like iron, nickel, etc. sank to the centre and formed the solid core of the earth.

The lightest elements like helium, hydrogen, oxygen, nitrogen, carbon, etc., occupied the atmosphere of the earth.

2. Formation of ammonia, water, and methane:

The prebiotic environment was very different from the present-day environment.

The primitive earth contained a large amount of hydrogen, nitrogen, carbon, and oxygen, among them, hydrogen was very active.

Hydrogen combined with nitrogen to form ammonia (NH₃), with oxygen to form water (H₂O), and with carbon to form methane (CH₄).

As the temperature was high, ammonia and methane remained as gases and water evaporated to form steam. Gradually, over the years, the temperature of the earth decreased.

Steam condensed into the water which resulted in the rain and the earth became cold.

Water gradually accumulated and this led to the formation of rivers, streams, lakes, seas, and oceans.

Compounds like ammonia, methane, etc. were dissolved in rainwater and accumulated in the sea. Thus, the first chemicals formed on the earth were water, ammonia, methane, etc.

3. Synthesis of simple organic compounds:

The next step in molecular evolution was the formation of micro-molecules.

As the earth surface considerably cooled, the highly reactive free radicals –CH and –CH₂ condensed to form a variety of both, saturated and unsaturated hydrocarbons.

The simple inorganic molecules of the ocean water interacted with one another to form simple organic molecules such as sugar, fatty acids, glycerol, amino acids, purines and pyrimidines.

The energy for these reactions was provided by the lightning, ultraviolet rays, volcanic activities and decay of radioactive elements.

CH₄ + NH₃ + H₂O → Amino acids

CH₄ + HCN + NH₃ + H₂O → Purines + Pyrimidines

CH₄ + H₂O → Sugar + Glycerol + Fatty acids.

Haldane described the sea containing molecules of these organic substances in abundance as ‘the hot dilute soup’ or ‘primitive broth’.

4. Formation of complex organic compounds:

The hot dilute soup was sterile and oxygen-free.

Simple organic substances came together in increasing numbers, they collided, reacted and aggregated forming new complex molecules such as polysaccharides, fats, proteins and purines and pyrimidines.

The protein molecules made their existence by polymerization of amino acids.

These proteins showed enzymatic reactions and were called protoproteins.

Due to their enzymatic nature, these proteins accelerated the rate of other chemical reactions.

The formation of protein molecules is considered a major milestone in the origin of life.

5. Formation of nucleic acids:

The next step in chemical evolution was the formation of nucleic acid.

It was formed by the aggregation of phosphoric acid, sugar, purines and pyrimidines.

They were linked in various combinations to form different types of nucleotides.

Thousands of nucleotides joined together to form a nucleic acid. The nucleic acids could self-replicate.

6. Formation of Protobiont or pre cells:

The nucleic acids along with inorganic and organic molecules formed the first form of life and were called protobionts or pre cells.

The proteins formed colloidal hydrophilic complexes surrounded by water molecules.

Oparin and Sydney Fox demonstrated the formation of these aqueous suspensions of polymers.

Oparin called these aggregates as Coacervates, while Sydney Fox called them Protenoids or Microspheres.

7. Formation of the First Cell:

The nucleic acids in pre-cells had the capacity to multiply but gradually they started a series of chemical reactions like protein synthesis.

That was the significant step in the transformation of pre-cell into a cell.

8. Biological evolution:

The first cells or primitive cells were marine and heterotrophic in nature.

Growth and multiplication of these cells caused depletion in the food and an increase in CO₂ due to fermentation.

These were the favourable circumstances for mutation, which resulted in the development of chromophores.

The chromophores had the ability to trap light energy and convert it into chemical energy.

This event helped in the transformation of heterotrophs into autotrophs.

Due to the release of oxygen as a by-product of photosynthesis, the primitive reducing atmosphere was slowly and gradually converted into an oxidizing atmosphere.

Describe Oparin - Haldane theory of chemical origin of life.

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