4. Theory of Chemical Evolution: . This theory was proposed by Oparin & Haldane They proposed that first life form could have come from pre- existing non- living organic molecules (like RNA, proteins, etc.) and that formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents The conditions on earth that favoured chemical evolution were very high temperature, volcanic storms & reducing atmosphere that contained methane, ammonia, water vapour etc. .
Experimental Proof for Chemical Evolution of Life. Stanley Miller & Urey created conditions similar to the primitive atmosphere in the laboratory using glass apparatus & tubes They created electric discharge using electrodes in a conical flask containing methane, ammonia, hydrogen & water vapour at 800 C. The water containing chamber was heated to provide water vapour. After a week, they observed the formation of amino acids. In similar experiments, many other scientists observed the formation of sugar, nitrogen bases, lipids, amino acids & even pigments Analysis of the meteorites also revealed the presence of similar compounds, indicating the occurrence of similar processes elsewhere in the space The chemical evolution of life was more or less accepted . . . . . .
Miller-Urey Electrodes Experiment slackarge sparks Water (lightning vapor Stopcocks for testing samples Mixture of gases ("primitive atmosphere") Condensor Water -Condensed liquid with complex molecules Heated water ("ocean")
Origin of First Life The first non- cellular form of life could have originated three billion years ago. They would have been giant molecule like RNA, proteins or polysaccharides These capsules were able to replicate/ reproduce The first cellular forms of life must have appeared about less than 2 billion years ago, they must have been single cells All life forms have appeared in water bodies. This is theory of abiogenesis, i.e., the first form of life arose slowly through evolutionary forces from non- living molecules; it is accepted by the scientists Once formed, these single cells must have evolved into the diverse complex organisms of today . . . .
Evolution of Life Several assumptions were to propose evolution of life of which the first was religious literature which tells us about the theory of special creation. . This theory has three connotations. One, that all living organisms (species or types) that we see, today were created as such. Two, that the diversity was always the same since creation and will be the same in future also. Three, that earth is about 4000 years old. These ideas were strongly challenged during the nineteenth century by Charles Darwin based on his observations made during a sea voyage in a sail ship called H.M.S. Beagle round the world He concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago. He said extinctions of different life forms took place also new forms of life arose at different periods of history of earth. . .
Atrica Tahiti 2nd H.M.S.Beagle Survey (1831-1836)
Organism has undergone gradual evolution due to variation of characteristics which enable some to survive better in natural conditions (climate, food, physical factors, etc.) would outbreed others that are less-endowed to survive under such natural conditions. It was referred as fitness of individual/ population which means reproductive fitness. Those who are better fit in an environment, leave more progeny than others which will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution. Alfred Wallace, a naturalist who worked in Malay Archipelago had also come to similar conclusions that Darwin had. . . . . .All the existing life forms share similarities and share common ancestors. However, these ancestors were present at different periods in the history of earth (epochs, periods and eras). They also concluded is that earth is very old, not thousand of years as was thought earlier but billions of years old. .
Geological History of Earth . With advancing studies on evolution scientists were able to . The geological time scale is divided into eras, periods & epochs conclude that Earth is billions of years old Rocks are formed by sedimentation a cross- section of earth's indicates the arrangement of the sediment one over the other during the long history of earth. Different sediments (of different ages) contain different life forms, which probably died during the formation of the particular sediment . .Certain organisms got extinct during these phases (Eg.- Dinosaurs) . Those found towards upper layer resemble modern organisms, while others in deeper layers were the simpler & older forms
Evidences for Evolution Evidences for evolution come from, Palaeontology, Embryology, . Comparative anatomy and morphology, Molecular homology & Biogeography Palaeontology: .Is a study of fossils found in the rocks to support organic evolution . Study of fossils from different sedimentary layers indicates: i. The geological time period in which the organisms existed ii. The life forms varied over time & certain life forms are restricted to certain geological life- span ii. The new forms of life that have appeared at different times in the history of earth
Embryos and Evolutionary History Gill slits Gill slits Tail Tail Fish Reptile Bird Human