The universe formed probably 12 to 14 billion years ago (Big Bang)
solar system came into existence 5-7 billion years ago
Initial stages of formation (4.5 bya) (impacted by another
planet – caused spin and tilt)
For nearly 700 million years – frequent and catastrophic
bombardment by meteorites of different sizes.
Gradually earth’s crust solidifieD.
Degassing: Methane, carbon dioxide, carbon monoxide,
ORIGIN OF LIFE
Life appeared 500 million years after the formation of earth,
i.e., almost 4 billion years back.
J. B. S. Haldane and the A. I. Oparin:
Life originated in the shallow seas from organic molecules
(amino acids, the building blocks of life)
Formed from inorganic substances (methane, ammonia)
Washed down from the atmosphere with torrential rains
Later Stanley Miller and Harold Urey provided experimental
support for this hypothesis. they successfully produced amino
1ST LIFE IN WATER
Unicellular bacteria: Single-celled bacteria (prokaryotic;
archebacteria) formed from organic molecules about 2000
mya in water
They lived on ocean floor near the vents of volcanic eruption
(survived on chemicals, not sunlight)
In course of time these organisms evolved into “Blue-green
algae” aka cyanobacteria (photosynthesis)
For a very long time (nearly 3 GY) after the origin of life, earth
had no life forms other than prokaryotes (cells lacking
nucleus) comprising different groups of bacteria.
Eukaryotes (cells with nucleus) probably appeared about a
BYA, but life was mostly in the form of single celled organisms
1ST LIFE ON LAND
Plants, amphibians, reptiles, Dinosaurs, small mammals(Rats),
Early human ancestors (2-5 million years ago)
Unknown: The mechanism of how non-cellular evolved into cells
is not known i.e. how a living organism got created from organic
The gradual development of something.
Charles Darwin (1809- 1882) wrote book “Origin of Species” (1859).
Living forms evolved by descent with modification from ancestral
Any population has built in variation which enable some to survive
better in natural conditions (climate, food, physical factors, etc.).
They outbreed others and leave more progeny. These are selected by
nature because of their fitness.
He called it natural selection and implied it as a mechanism of evolution