7. EVOLUTION
A BRIEF ACCOUNT OF EVOLUTION
The
geological time scale includes 4 eras: Proterozoic, Palaeozoic, Mesozoic
& Cenozoic.
1. Proterozoic era: 2500 - 541 million yrs ago (mya)
-
2000 mya: First cellular forms of life appeared.
-
Some
of the cells had the ability to release O2 as the light reaction in
photosynthesis.
-
Single
celled organisms became multicellular organisms.
2. Palaeozoic era
(540 - 252 mya)
- It has 6 periods: Cambrian
(540 - 490 mya), Ordovician (490 - 443 mya), Silurian (425 mya), Devonian (405 mya), Carboniferous
(360 mya) & Permian (285 mya).
-
500 mya: Invertebrates were formed.
-
450 mya:
First land organisms (plants) appeared.
-
400 mya: Arthropods invaded the land.
-
350 mya: Jawless fishes were evolved.
Lobefins (stout & strong finned fishes) could move on land and go back to
water. They evolved to first amphibians (ancestors
of modern day frogs & salamanders).
In 1938, a lobe-fin
called coelacanth fish was caught in South Africa which was thought to
be extinct.
-
320 mya: Sea weeds and few plants were existed.
-
Amphibians evolved to
reptiles. They lay thick-shelled
eggs (do not dry up in sun).
-
Giant ferns
(Pteridophytes) were
present but they all fell to form coal deposits slowly.
3. Mesozoic era (252 - 66
mya)
- Age
of reptiles and gymnosperms.
- It has 3 periods: Triassic
(230 mya), Jurassic (208 mya) & Cretaceous (144 mya).
-
200
mya: Some of the land reptiles went back into water to evolve into fish-like
reptiles (E.g. Ichthyosaurs).
-
The
land reptiles were dinosaurs (Tyrannosaurus rex, Triceratops, Stegosaurus,
Brachiosaurus etc.)
T.
rex was the largest dinosaur (20 feet in height, huge fearsome dagger-like teeth).
-
Toothed birds were
emerged.
4.
Cenozoic era (66 -
0 mya)
- Age of Mammals & Angiosperms.
- It has 2 periods: Tertiary
(66 mya) & Quaternary
(2 mya - Age of man).
- 65
mya: Dinosaurs
suddenly disappeared. Some say climatic changes killed them. Some say most of
them evolved into birds.
- First mammals were shrew-like. Their fossils are small sized.
- In South America, there
were mammals resembling horse, hippopotamus, bear, rabbit etc. Due to continental
drift, when South America joined North America, these animals were overridden
by North American fauna.
- Due to continental drift,
Australian marsupials survived because of lack of competition from any other
mammals.
ORIGIN AND EVOLUTION OF MAN
· 15
mya: Dryopithecus &
Ramapithecus.
Hairy. Walked like gorillas & chimpanzee.
Dryopithecus: ape-like.
Ramapithecus: man-like.
· 3-4
mya: Man-like primates walked up right in eastern
Africa.
Height up to 4
feet. This belief is based on fossils of man-like bones found in Ethiopia &
Tanzania.
· 2
mya: Australopithecus. Lived in East African grass lands. Hunted with
stone weapons. Ate fruits.
Homo
habilis: First
human-like being (hominid).
Brain capacity: 650-800 cc. Did not eat meat.
· 1.5
mya: Homo erectus (Java man). Large brain (900 cc). Ate meat.
· 1
lakh - 40,000 yrs ago: Homo neanderthalensis
(Neanderthal man).
Brain capacity: 1400 cc. Lived in East &
Central Asia. Used hides to protect their body. Buried their dead.
· 75,000
- 10,000 yrs ago
(ice age):
Homo sapiens (Modern
man).
Pre-historic cave art developed about 18,000
years ago. E.g. Cave paintings at Bhimbetka rock shelter in Raisen district of Madhya
Pradesh.
Agriculture & settlements: 10,000 years
ago.
Sequence of Human evolution:
Dryopithecus → Ramapithecus
→ Australopithecus → Homo
habilis → Homo erectus → Homo neanderthalensis →
Homo sapiens