#Origin and evolution of life pdf series

The primitive inorganic molecules later interacted with another to form simple organic compounds, namely, sugars, fatty acids, glycerol, amino acids and organic bases (purines and pyrimidines). The energy for the formation of molecules might have come from reflected solar radiations, lightning or volcanic eruptions. The earliest molecules have been the formed gases and inorganic compounds, namely, hydrogen (H 2), nitrogen (N 2), ammonia (NH 3), methane (CH 4), carbon dioxide (CO 2) and water vapour (H 20). The atmosphere was highly reducing and oxygen in molecular form was not available. This primary abiogenesis is thought to have occurred about 3.6 billion (3600 million) years ago.

#Origin and evolution of life pdf series

Haldane, a british scientist suggested in 1929 that life must have arisen on the primitive earth from a collection of chemicals through a progressive series of chemical reactions in which atoms combined into inorganic molecules, inorganic molecules into simple organic compounds, simple organic compounds into complex organic compounds (polymers), and polymers into aggregates, which finally got organized into the living matter. This concept was put forward by Alexander. (4) Abiogenic or naturalistic theory or chemical origin of life:В Life originated from inanimate matter by a series of chemical reactions on the primitive earth. This theory is also called theory of panspermia.Д«ecause of hazards like low temperatures, very high influx of cosmic and UV radiation, lack of atmosphere, extreme dryness etc, that exist in the interplanetary space and are not conducive to life, this theory of origin of life was rejected The latter grew and then evolved into various existing forms. (3) Cosmozoic or interplanetary theory:В life could have originated once or several times in various parts of the galaxy in universe and it reached the barren earth from some other heavenly body in the form of resistant spores or seeds. Since then, it is being widely accepted that life originates from pre-existing life- biogenesis. Louis Pasteur (1862) who experimentally proved that microorganisms, such as protists and bacteria, arise from the pre-existing microorganisms of their kind. Fly larvae were believed to develop from rotten meat frogs, snakes and crocodiles could form from the moist soil (mud) of the river. (2) Theory of spontaneous generation: It stated that life originated spontaneously from non-living materials- abiogenesis. The theory of special creation is purely a religious concept. Manu and Shradha were the first man and woman respectively. According to Hindu mythology, Lord Brahma created the world with his wish. Adam and Eve were the first man and woman created by God. God created the universe, plants, animals and human beings in six natural days. (1) Theory of special creation: It stated that life was created by the wishes of a divine being or some supernatural power, the Creator or God out of nothing at a particular time in the remote past. The latter kept revolving round the sun in different elliptical orbits. These clumps finally swept up more particles and grew into different sized planets.

Atoms and dust particles orbiting around the central mass, i.e., sun then aggregated into clumps (about the size of asteroids). As the sun condensed, it became hotter and brighter due to conversion of gravitational energy into heat. The central mass condensed further and formed the sun. The whole matter condensed under the force of its own gravity to become a flattened spinning disc of atoms and dust particles. As this cloud condensed, the rotational movement threw a ring of cloud which kept on rotating around the central mass. Our solar system was formed about 4-5 billion (4500 million) years ago from a huge, spinning cloud of cosmic dust and gas called solar nebula. Sun is one of the millions of stars of our galaxy. Our galaxy is called Akash Ganga or The Milky Way. These galaxies appear to be moving away from one another at a speed nearly equal to the speed of light. This big explosion threw out numerous pieces of cosmic material (nebulae) which slowly condensed and became organized slowly into groups of stars called galaxies. According to Big Bang Theory, some 15 billion years ago, the universe originated by a big bang (thermonuclear explosion) of a dense entity.