LIFE ON EARTH

PRE-LIFE EVENTS

  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,
ammonia etc.

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
{primordial soup}

EVIDENCE:

   Later Stanley Miller and Harold Urey provided experimental
support for this hypothesis. they successfully produced amino
acids

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

Origin of life

 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
materials

EVOLUTION

 The gradual development of something.
Charles Darwin (1809- 1882) wrote book “Origin of Species” (1859).
 Living forms evolved by descent with modification from ancestral
forms.

Mechanism:

 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

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