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
|
Very clear and nice explanation sir
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