Biology EVOLUTION

Origin of Universe and Earth

when 'life' originated on earth. The branch of life science for the study of 'Origin of life' and evolution of different forms of life on earth was called Bio-evolution or Evolutionary Biology by Mayer, (1970).

The study of universe or cosmos is called Cosmology. Our earth belongs to the Solar system having nine stars called planets constantly rotating around a common Sun. On the basis of the order of the distance from the sun these planets include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto while moon is a satellite of earth. The universe is made up of matter and energy and it was formed about 10 to 13 billion years ago as a red hot, dense, rotating gaseous cloud of cosmic dust called Ylem or primaeval matter. The Ylem consisted of particles of matter (like neutron, proton and electron) and antiparticles of antimatter. Scientists like Lemaitre (1931), Gamow (1948), Dicke (1964) etc. supported the Big-Bang Hypothesis which explains that collision between these particles and antiparticles caused a tremendous explosion to form atoms of hydrogen. Cosmic evolution began with the fusion of hydrogen atoms with progressively heavy atoms of different elements. Stellar systems and stars were formed by spreading of original gaseous cloud into the space and divided into smaller and larger masses. Most of the stars are masses of red hot gases even today.

Kant (1755) and Laplace (1796) supported Nebular Hypothesis which explains our solar system to have evolved about 4.5 to 5 billion years ago from a rotating red-hot gaseous cloud containing millions of free atoms of different varieties. First of all sun was formed when this cloud condensed, next the planets were thrown off from the sun and later on, in turn satellites were thrown off by planets. However, Nebular hypothesis was rejected by astronomers of present century like Weizsacker (1944), Alfen (1950) and Hoyle (1955).

According to them the sun was originally surrounded by a disk of rotating gas. Later many rotating concentric whorls were formed by break up of the disc and by gravitation and rotation particles of each whorl collected and condensed to form a planet. Our earth was formed about 4.6 billion years ago as a red hot gaseous cloud of free atoms with temperature of 5000o to 6000oC.

Structure of present earth. The earth is orange like in shape. Its pole to pole diameter is 12640 km and equatorial diameter is 12783 km. It is about 15 crore km away from sun and about 484000 km away from moon. Due to tremendous temperature gases existed in atomic form but gradually they cooled down in hundreds and millions of years into molten core. According to density other elements got stratified. Earth contains the central solid core, the middle mantle and shell and outer crust. The earth rotates at its polar axis in one day and it rotates around the sun in 365 days or one year.

Origin of Life

Life is the part and parcel of the universe and both are very intimately associated with each other. We know that �Life is the most unique, complex organisation of molecules, expressing itself through chemical reactions which lead to growth, development, responsiveness, adaptation and reproduction� that matter has achieved in our universe. Origin of life is a unique event in the history of universe.

(i) Ancient theories of origin of life : Various theories have been put forward to explain the phenomenon of origin of life. A few of them were only speculations while others were based on scientific grounds. These theories are �
(a) Theory of special creation.
(b) Theory of spontaneous generation or Abiogenesis
(c) Biogenesis
(d) Cosmozoic theory
(e) Theory of sudden creation from inorganic material.
(f) Naturalistic theory

(a) Theory of special creation :
According to a Spanish Priest Father Suarez (1548 � 1617 B.C.), the whole universe was created in six days by the God. First day Earth and heaven, second day sky, third day dry land and vegetation, fourth day Sun, Moon and other planets, fifth day fishes and birds, and sixth day human beings other animals were created by God. This theory was based on some super natural power.

Theory of spontaneous generation or Abiogenesis

This theory postulates that life originated from non-living matter spontaneously from time to time. This theory was supported by Plato, Aristotle, Anaximander, John Ray, Needham, Von Helmont, etc., upto the end of seventeen century. Huxley (1870) criticised this theory and propounded the theory �life originated from preexisting life only.�
 Abiogenesis means origin of life from non-living organisms.

Biogenesis

Biogenesis : Scientists like Redi (1668) Spallanzani (1767), Louis Pasteur (1866�1862) provided experimental support for the Biogenesis concept of Huxley.
Francesco Redi (1668) showed that maggots could not be created from meat. Actually, the smell of meat attracts flies which lay eggs on the flesh. These eggs hatched into flies.
Spallanzani (1767) showed that even primitive, unicellular organisms cannot arise from non-living matter.
Louis Pasteur (1860-62) obtained air samples in the flasks of broth (yeast and sugar solution) whose drawn-out necks were sealed cooling these contained a partial vaccum. Where a sample was required, the flask was opened. Air was drawn in and the flask was resealed. Flasks were incubated. These flasks which were opened in the streets became turbid while those exposed to dust-free air rarely contained bacteria.

Louis Pasteur also, used swan-necked flasks whose long, curved necks permitted exchange of air between outside and inside of the flask, but dust and bacteria were trapped along the wall of the neck. On tilting the flask, the bacteria got washed down into the broth, so that the latter became cloudy due to bacterial growth.

Oparin's Modern Theory

Oparin (1924) proposed that �life could have originated from non-living organic molecules.� He believed in Biochemical origin of life. Haldane (1929) also stated similar views. Oparin greatly expended his ideas and presented them as a book �The origin of life� in 1936.

According to this theory, the Earth originated about 4,500 million years ago. When the earth was cooling down, it had a reduced atmosphere. In this primitive atmosphere nitrogen, hydrogen, ammonia, methane, carbon mono-oxide and water were present. Energy was available in the form of electric discharges by lightening and ultraviolet rays. As soon as the earth crust was formed, it was very much folded. Torrential rains poured over the earth for centuries and were deposited in deep places.

The atmospheric compounds, inorganic salts and minerals also came in deep places oceans, these molecules gave rise to a variety of compounds and finally to the self-duplicating molecules. Ultimately these molecules were enclosed in membranes derived from lipids and proteins, along with water and chemical compounds, giving rise to cell like units. Again random combinations may have led to the formation of chlorophyll� containing organisms which could produce their own food (autotrophs) by a process called photosynthesis. These organisms had a better chance to live because they synthesise starch from carbon dioxide and water in presence of sunlight. Starch could be used as further source of energy. During photosynthesis, oxygen was produced. The oxygen was used by other organisms for respiration. Also oxygen, when acted upon by ultraviolet rays, formed ozone layer through which ultraviolet rays cannot pass. This layer is formed about 25 km. from earth's surface. After the formation of ozone layer, organisms could come to the surface of the ocean and could survive even on land, if thrown out of oceans. The Oparin's and Haldane's theory of origin of life is most accepted these days as it is supported by Miller's experiment duly supported by David Buhal, Melvin Kelvin's experiment etc.
 Oxygen is absent in the primordial atmospheres at the time of origin of life.

Miller's Experiment

Miller's Experiment : An American scientist (Biologist) Stanley Miller (1953) performed an experiment under support Oparin's theory of origin of life. He believed that basic compounds which are essential for life can be synthesised in the laboratory by creation in the laboratory, on a small scale, the conditions which must have existed at the time of origin of life on earth.
Miller took a flask and filled it with methane, ammonia and hydrogen in proportion of 2:1:2 respectively at 0C. This proportion of gases probably existed in the environment at time of origin of life. This flask was connected with a smaller flask, that was filled with water, with the help of glass tubes. In the bigger flask, two electrodes of tungsten were fitted. Then a current of 60,000 volts was passes, through gases containing bigger flask for seven days. At the end of seven days, when the vapours condensed, a red substance was found in the U-tube. When this red substance was analyzed, it was found to contain amino acids, Glycine and nitrogenous bases which are found in the nucleus of a cell.
 An experiment to prove that organic compounds were the basis of life, was performed by miller.

From the above theory we conclude that life first originated in water. Therefore, water still continues to be an essential constituent of life.