Origin of life
- The universe or cosmos is about 20 billion years old. There are several theories regarding the origin of universe, but the most accepted theory is Big Bang theory. Which was produced by Abbe Lemaitre
- Solar Nebula Hypothesis is one of the most popular hypothesis to explain the origin of solar system. which was proposed by Kent.
- According to theory of special creation which was supported by Father Suarez, life was created by supernatural power that lacks scientific power that lacks scientific evidence, on account of which it is not accepted.
- Greek philosophers like Thales, anaximander, Xenophanes, Plato, Aristotle, Van helmont supported spontaneous generation (or) abiogenesis, which had stated that life originated from non living mater [decay/rotting matter]. This theory is also discarded as it had no scientific evidence.
- Cosmozoic theory/theory of panspermia, as proposed by Ritches, Helmholtz and Arrhenius units of life called spores or cosmozoa has reached the earth from some other heavenly body. The theory is not accepted.
- Theory of catastrophism [proposed by George Cuvier]. According to the theory catastrophic revolution happens in earth from time to time which destroys all organisms and then the new organisms originate from in organic matter.
- According to Biogenesis, life originated from pre-existing life. The theory was developed by Redi and Spallanzani and Louis Pasteur, who opposed spontaneous generation
Chemical origin of life : [Chemical Evolution / Chemogeny]
- Early earth had innumerable free atoms of all those elements Eg. C, H, O, N, P, S which are essential for the formation of protoplasm. This led to the formation of primitive atom.
- As the earth cooled free atoms of different elements came together and formed simple molecules such as H2, N2, H2O, CH4, NH3, CO2. First 'H' atoms combined with all 'O' atoms to form water and left no tree O2 and hence the atmosphere is called reducing atmosphere.
- Next step is the formation of simple organic molecules (monomers) such as simple sugars, nitrogenous bases, amino acids, glycerol, fatty acids etc.,
- Formation of complex organic molecules
sugar + sugar + .... → Polysacharides
Fatty acids + glycerol → Phospholipids, Fats
Aminoacids + amino acids → Polypeptides, proteins
N2 bases + penlose sugars + phosphoric acid → Nucleotide
Nucleotides + Nucleotides → Nucleic acids
- Synthesis of complex organic molecules must have occurred in sea which had been described by Haldane as the Hot dilute soup called pre-biotic soup
- Miller circulated a mixture of methane, Ammonia and Hydrogen in the ratio of 2 : 1 : 2 is a air tight apparatus and passed electrical discharges from electrodes at 800°C
- He found a large number of simple organic molecules including some amino acids such as glycine, Alanine and Aspartic acid. [other substances : Urea, HCN, Lactic acid, Acetic acid]
Watch this video for the topic from 0:07 to 14:47
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