WHAT ARE THE EVIDENCES FOR EVOLUTION? NEET (part-1)

  • 7.3 WHAT ARE THE EVIDENCES FOR EVOLUTION?

    • Evidence that evolution of life forms has indeed taken place on earth has come from many quarters. 
    Paleontological evidence.
    • Fossils are remains of hard parts of life-forms found in rocks. 
    • father of Indian paleontology- Birbal Sahani
    • Rocks form sediments and a cross-section of earth's crust indicates the arrangement of sediments one over the other during the long history of earth. 
    • Different-aged rock sediments contain fossils of different life-forms who probably died during the formation of the particular sediment. 
    • Some of them appear similar to modern organisms. 
    • They represent extinct organisms (e.g., Dinosaurs). 
    • Birds are the only surviving dinosaurs.
    • A study of fossils in different sedimentary layers indicates the geological period in which they existed. 
    • The study showed that life-forms varied over time and certain life forms are restricted to certain geological timespans. 
    • Hence, new forms of life have arisen at different times in the history of earth. 
    • All this is called paleontological evidence. 
    • Do you remember how the ages of the fossils are calculated? Do you recollect the method of radioactive-dating (using half-life) and the principles behind the procedure?
    Methods:
    • Uranium-lead method: this include decay of U235 in 4.5 billion years to Pb206 
    • Carbon-Nitrogen method (W. F. Libby 1950): it is based upon the decay of C14 into N14 in 5630 years decay.
    • Potassium-Argon method: the half-life of potassium (K40) is 1.3x10years 
    • Electron-spinning Resonance method (ESR): relatively most accurate of dating the fossils.
  • types:
       

    Fossils
    Mode of formation
    Example
    1
    Unaltered (preserved)
    Whole body is found frozen or amber
    Wooly mammoths (ice), insects (amber) and mummies
    2
    Altered of petrified
    Replacement of organic part with mineral deposits
    Bones, shell, teeth, wood etc.
    3
    Coprolite
    Faecal pellets
    Coenozoic animals
    4
    Moulds and casts
    Individuals have been completely lost but the molds true copies of their shape
    Gastropods (Molluscs) from Portland
    5
    Impression
    Remains in the fine grained sediments on which organism dies.
    Archaeopteryx feathers, leaf
    6
    Imprints
    Foot prints trails, tract of organism.
    Dinosaurs foot prints, print of leaf, skin, wings
    7
    Compression
    Main tissue part disappears but the hard outer tough part remain intact in the rock.
    Plants

    Missing links: Archaeopteryx a missing link between reptile and birds. (no sample is available now hence called as missing link)
    Connecting link: 
    Connecting links
    Between
    Virus
    Living and non lilving
    Blue-green algae
    Prokaryotic and Eukaryotic
    Euglena
    Autotroph and heterotroph
    Slime molds
    Protista and fungi
    Proterospongia
    Protozoa and sponge
    Neopilina
    Annelida and Mollusca
    Paripatus
    Annelida and arthropoda
    Chimaera
    Osteichthyes and chondrichthyes
    Latimeria (lung fish)
    Fish and amphibian
    Archaeopteryx
    Reptiles and birds
    Prototherians or monotremata (Echidna, ornithorynchus (platipus)
    Reptile and mammals

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