A Brief Account of Evolution Video Lecture | Biology for SSS 3

brief account of evolution about 2000
million years ago the first cellular
form of life appeared on earth slowly
single-celled organisms became
multicellular life forms 500 million
years ago invertebrates were formed and
active 350 million years ago jawless
fish probably evolved 320 million years
ago seaweeds and few plants existed the
first organisms that invaded land where
plants they were white spread on land
when animals invaded land 350 million
years ago fish with snout and strong
fins could move on land and go back to
water
1938 coal cans fish caught in South
Africa was extinct lip fins evolved into
the first amphibians these were
ancestors of modern-day frogs and
salamanders the amphibians evolved into
reptiles they lay thick shell eggs which
do not dry up in the Sun 200 million
years ago reptiles of different shapes
and sizes dominated on earth 200 million
years ago some of the land reptiles went
back to water and evolved into fish like
reptiles ate fear sores in the land
reptiles the biggest one was
tyrannosaurs which was 20 feet in height
and had huge dagger-like teeth 60
million years ago the dinosaurs
disappeared from earth the reason may be
due to climatic changes but most of them
evolved into birds the first mammals
were like shoes their fossils a
small-sized mammals are viviparous and
protected there
unborn young inside mother's body when
reptiles come down mammals took over
this earth they were in South America
mammals resembling halls hippopotamus
bear rabbit etc due to continental drift
when South America joined North America
these animals were overridden by North
American fauna due to the same
continental drift pouched animals of
Australia survived because of lack of
competition from any other mammals some
animals wholly live in water example
whales dolphins seals and sea cows