Bio Chemical evolution It is generally agreed by Astronomers, Geologist and Biologist that the earth is about 4.5 to 5 thousand million years old. This theory is the most accepted theory in the field of evolution. According to this theory evolution is occurred in following steps:- 1. Formation of the earth:- According to this theory this earth or, universe was created by a hypothetical masses called yleum from which all the elements are substances are formed. 2. Chemogeny or, Cognogeny or, Inorganic evolution:- In this step organic compounds are formed by the inorganic compounds available in previous atmosphere. 3. Biogeny or, Organic evolution:- In this step simple life was formed by organic compound and gradually complex life was originated from simple life. 1. Formation of the earth or, Primitive earth Scientists believe that first earth was filled with hot gases and vapours of elements due to heat of the earth. The elements with heavy atomic masses like Fe, Co, Ni etc are attracted by the more force of gravitation formed the core of the earth. (According to law of gravitation force of attraction produced between two bodies is directly proportional to the product of their masses.) The lighter elements like Aluminium, Silicon, Phosphorous, Sulphur etc. formed the surface of the earth because of less force of attraction whereas the light elements like Hydrogen, Oxygen, Nitrogen, Carbon etc formed the gaseous envelop around it called atmosphere. 2. Chemogeny:- Oparin and Haldane hypothesis:- The organic compounds had existed on the earth before the origin of living things and the living things have evolved from these pre existing compounds.
They assume that oxygen was present in atmosphere in combined form with hydrogen. It means only water contains oxygen in previous atmosphere. As we know that hydrogen is the most reactive elements among the elements present in previous atmosphere. So, hydrogen reacted with carbon to form different types of saturated, unsaturated, stable and unstable hydrocarbon mostly methane. Nitrogen was present in combined state with hydrogen in the form of Ammonia. For reactions it gets energy from heat of the earth and from the sun. Even hydrogen was present in free state too but in very little amount. Miller and Urey experiment:- S. L. Miller and Urey (1953) have done an experiment on the Oparin and Haldane hypothesis. They have set up the apparatus and provide previous atmospheric conditions for the formation of organic compounds from inorganic compounds except Methane. They have set up a closed apparatus in which mixture of methane, ammonia, water and hydrogen (gases present in previous atmosphere.) passes through electric discharge chamber where electric spark is given which resemble to the lightning and thundering of previous atmospheric condition, passes through cooling jacket where it gets low temperature as it was in night the temperature of atmosphere was low and
passed through round bottom flask where it was heated slowly with spirit lamp it was resembled to heat radiate by the earth. This set up was left in sun for approximate one week. After one week it has been seen there are different types of amino acid was formed. Formation of hydrocarbon:- Earth continues cooling down when temperature of the earth is reached at 100 0 C or, low then free atoms of hydrogen and carbon react together to form saturated and unsaturated hydrocarbon. e.g. C + H 2 = CH CH + CH = C 2 H 4 CH 2 + CH 2 = CH 4 + C Formation of aldehyde and ketone:- As we know that unsaturated hydrocarbon is more reactive. So, these are react with steam to form aldehyde. e.g. C 2 H 2 + H 2 O = H 3 CCHO Formation of carbohydrate, Adenine, nucleoside and nucleotide:- Ultraviolet irradiation of formaldehyde formed ribose, deoxyribose sugar. In the sea, glucose molecules joined together to form starch and other carbohydrate. Adenine can be synthesized by electron irradiation on the mixture of methane, ammonia and water or, from ammonium cyanide. When a dilute solution of adenine is exposed to ultraviolet light nucleoside will be formed. On further irradiation nucleotide is detected. Biogeny:- Formation of Nucleic acid:- A large number of such nucleotides were combined to form DNA or, RNA. As we know that DNA is self reproducing unit. So, it is first sign of life. The solution of such organic and inorganic substances which was capable to form life is called primordial soup.
Formation of Coacervates:- The aggregation of organic and inorganic substances surrounded by thin layer of water is called coacervates or, microsphere. It has capacity to absorb organic substances from its surrounding and can grow in size as well as can divide. Formation of eobionts or, pre cell or, protobionts:- The coacervates got nucleic acids and different types of protein from its surrounding or, may be developed inside it and bounded by a very thin layer of fatty acids. It started to use its protein as an enzyme for metabolic functions. Such hypothetical first living structure is called eobionts, pre celll or, protobionts. First cell In addition to DNA and RNA different kinds of organic and inorganic molecules accumulated and these became surrounded by a thin membrane. This was the first cell i.e. prokaryotic cell. e.g. Bacteria, Blue green algae etc. Slowly other molecules aggregated around the primitive cell and formed another membrane called cell membrane. This is the eukaryotic cell. Cognogeny:- Life was possible in water not on land because ozone layer was not present earlier. Ultraviolet light directs come to land and could destroy life. But it can absorb by water. So, first cell cane into existence in water. Due to shortage of food materials in water, organisms changed their feeding habitat and became parasitic, saprophytic, chemosynthesizers, photosynthetic etc. The formation of diversed and complex form of life from simple life is called cognogeny. Origin of autotrophs:- Due to lack of organic materials, some prokaryotes evoluted to form organic materials from inorganic substances. This wasa supposed to beginning of autotropism. The source of energy for autotropism was anaerobic breakdown. Such autotrophs are called chemoautotrophs. e.g. Sulphur bacteria Chemical energy 6CO 2 + 12 H 2 S C 6 H 12 O 6 + 6 H 2 O + 12 S Some prokaryotes could absorb solar energy and synthesized carbohydrates.
6CO 2 + 12 H 2 S Solar energy C 6 H 12 O 6 + 6 H 2 O + 12 S In some organisms molecular changes occurred and get chlorophyll. They start to do photosynthesis. 6CO 2 + 12 H 2 O Solar energy Chlorophyll C 6 H 12 O 6 + 6 H 2 O + 6 O 2 Formation of Ozone layer:- Oxygen produced during photosynthesis changed atmosphere. Reduced atmosphere is changed into oxidizing atmosphere. Due to irradiation of ultraviolet ray oxygen is changed into ozone which makes life possible on land.