Origin of the Oparin, Haldane and Miller Molecules

Introduction:

Oparin Haldane and Miller

The universe is an old vast and empty space comprising galaxies and is said to have originated around 20 billion years ago. The Big Bang Theory is the most accepted theory that explains the origin of the planet Earth.

This theory suggests that the universe is a result of a massive explosion that occurred 20 billion years ago. After the explosion, the atmospheric condition stabilized, and the temperature reduced. As a result, gases like hydrogen and helium formed which led to the formation of galaxies of today.

Scientists believe that the Earth originated about 4.5 billion years ago. The Earth’s primitive atmosphere was very hot and had various gases of several elements. As time passed, the Earth gradually cooled down and the gases condensed resulting in the formation of a solid crust. Thousands of years of torrential rains resulted in the formation of large water bodies like oceans.

The early atmosphere had large quantities of gases like hydrogen, nitrogen, water vapor, carbon monoxide, methane, and ammonia. A series of chemical reactions took place among these gases which led to the origin of life on earth.

Explanation:

The origin of life has been explained by various scientists who put forward their theories to explain how the first life was formed. Some of these theories include:

1. Theory of special creation
2. Theory of panspermia
3. Theory of spontaneous generation
4. Theory of biogenesis
5. Theory of chemical evolution

Theory of Special Creation:

It is the oldest theory and is based on conventional religious beliefs. It is not backed by any scientific evidence. The theory stated that life was created by a supernatural power. It was proposed by Father Suarez.

This theory suggested that the earth was 4000 years old and all life forms on earth were created as such. It also states that the diversity of life forms has always been the same since the time of creation and will remain the same in the future as well.

Theory of Panspermia:

This Theory states that life did not arise on planet Earth and was proposed by Helmholtz (1884). He claimed that cosmozoa/panspermia, or microorganisms or spores from space, arrived on Earth with meteorites and comets and then evolved into higher organisms in the water.

Theory of Spontaneous Generation (Abiogenesis):

This theory stated life originated from non-living matter spontaneously. Aristotle proposed that life arose from non-living material if the material contained pneuma, i.e., vital heat.

Some examples of this theory include:

• Damp hay and corn in a dark corner gave rise to mice
• Earthworms fell from the sky when it rained

Many scientists and philosophers supported this theory. Later, the theory was disapproved by Louis Pasteur.

Theory of Biogenesis:

This theory states that living organisms are always produced from pre-existing living forms by a process called reproduction. Louis Pasteur with his experiment proved that living things come only from other living things.

The Theory of biogenesis, however, could not explain the origin of the first life on earth but could explain only the continuity of life.

Theory of Chemical Evolution:

This theory suggests that life originated on earth by combinations of various chemicals through constant chemical reactions over a long period. This theory is also called the self-assembly theory of the origin of life or the biochemical origin of life.

This theory was first hypothesized by Haeckel but later developed by the Russian scientist Alexander I. Oparin (1924) and British biologist J. B. S. Haldane (1929).

The process of chemical evolution can be divided into the following steps:

a. Origin of Earth and Primitive Atmosphere:

The Big Bang theory of Georges Lemaitre explained the origin of the Universe. As per this theory, the Universe originated about 20 billion years ago by a single huge titanic explosion.

As the Universe kept expanding, the temperature decreased, and various galaxies containing solid objects were formed. The Milky Way is one such galaxy, and Earth is one of the planets of the solar system, which originated about 4.6 billion years ago.

When formed, it was a rotating cloud of hot gases and cosmic dust called Nebula. The condensation and cooling resulted in stratification, and the heavier elements like nickel and iron passed to the core, and lighter ones like helium, hydrogen, nitrogen, oxygen, carbon, etc., remained on the surface.

They formed the atmosphere of the Earth. Earth’s primitive atmosphere was quite different from the present one, and it was of a reducing type, which means free oxygen was absent.

b. Formation of Ammonia, Water, and Methane:

As the primitive atmosphere began to cool down, the lighter elements started reacting with each other. The early atmosphere was abundant in hydrogen, carbon, nitrogen, and sulfur, of which hydrogen reacted with other elements to form chemicals like CH4, NH3, H2O, and H2 S.

c. Formation of Simple Organic Molecules:

As the temperature of the earth decreased, the steam condensed into water and resulted in heavy rainfall, which gradually cooled the Earth. Rainwater accumulated on the land to form rivers, streams, lakes, seas, and oceans.

At that time, the atmosphere did not contain an ozone layer, and thus ultra-violet radiation reached the surface of the earth directly. Under the influence of available energy sources such as UV rays, radiations, lightning, and volcanic activities, the early molecules of hydrocarbons, ammonia, methane, and water underwent several reactions like condensation, polymerization, oxidation, and reduction.

These reactions resulted in the formation of simple molecules like monosaccharides, amino acids, purines, pyrimidines, fatty acids, glycerol, etc. and accumulated at the bottom of water bodies. Haldane described this as ‘‘hot dilute soup’ or ‘‘primitive broth.’ It did not show any degradation due to the absence of free oxygen and enzymes.

d. Formation of Complex Organic Molecules:

The primitive broth was neutral and oxygen-free. Simple organic molecules aggregated to form new complex organic molecules like polysaccharides, fats, proteins, nucleosides, and nucleotides due to polymerization.

Polymerization of amino acids formed proto proteins which later formed proteins. The formation of protein molecules is considered a landmark in the origin of life. Proteins (enzymes) increased the rate of other chemical reactions.

e. Formation of Nucleic Acids:

Nucleotides may have formed due to the reaction between phosphoric acid, sugar, and nitrogenous bases. Many nucleotides join to form nucleic acids (RNA, DNA). Nucleic acids acquired self-replicating ability.

f. Formation of Photobionts or Procells:

Protobionts are the first form of life. They are prebiotic chemical aggregates having some properties of the living system. They have formed due to coacervation, i.e., aggregation of organic molecules. Oparin (1924) called them coacervates.

g. Formation of the First Cell:

When RNA or DNA systems evolved within protocells, they resembled bacteria or viruses. They controlled various metabolic activities. The first cell was anaerobic and heterotrophic and obtained energy by chemoheterotrophic processes.

Experimental Evidence of Chemical Evolution:

Stanley Miller and his teacher Harold Urey provided the first experimental evidence in support of the chemical evolution theory of Oparin in 1953.

They designed a glass apparatus which was called spark-discharge apparatus. The apparatus was first sterilized and then evacuated. Gases such as methane, ammonia and hydrogen were pumped in the proportion of 1:2:2 into the glass chamber. A tube carrying water vapor was also connected to the chamber. The lighting effect was stimulated by electric discharge carbon arc spark in the chamber.

The mixture of CH₄, NH₃, and H₂ was continuously exposed to electric discharge for several days causing the gases to interact and then condense. The liquid that was collected in the U-tube turned brown. When this liquid was analyzed, it reported the presence of simple organic compounds. (Urea, amino acids, lactic acid, etc.).

This experiment provides evidence that the simple molecules present in the earth’s early atmosphere combined to form the organic building blocks of life.