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 1.3x10⁹ years 
  • 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