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Evolution (part1)
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Introduction, Theories of origin of life.

Shivam Sharma
Learning and teaching Biology, pursuing medical studies at TU.

Unacademy user

  2. Introduction Evolution is the change in the inherited characteristics of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organization, including species, individual organisms and molecules such as DNA and proteins LI

  3. Origin of Life The origin of life is considered a unique event in the history of universe The Universe Universe is about 20 billion years old It includes huge cluster of galaxies, which contain stars and clouds of gas and dust The Big Bang theory explains origin of universe which states that the universe arose from a huge explosion unimaginable in physical terms) of large entity As the universe expanded, the temperature decreases; hydrogen & helium were formed sometime later The gases condensed under gravitation & formed the galaxies of the present day universe In the solar system of the milky way galaxy, earth was supposed to have been formed about 4.5 billion years back . . . . .

  4. The Earth Earth was formed 4.5 billion years before . Water vapour, methane, ammonia & carbon dioxide were released from the molten mass The UV rays from the sun broke up water into hydrogen & oxygen The lighter hydrogen gas escaped from the surface while oxygen combined with other compounds (methane, ammonia etc.) to fornm water, carbon dioxide etc. As the water vapour cooled, the water fell as rain & filled all depressions to form oceans & other water bodies . . .From the oxygen, ozone layer was also formed Life started appearing (origin of life) about 500 million years after the formation of earth i.e., about four billion years ago .

  5. Theories of Origin of Life Various theories were proposed to explain the origin of life: 1. Theory of Special Creation 2. Theory of Panspermia/ Cosmozoic theory 3. Theory of Spontaneous Generation 4. Theory of Chemical Evolution

  6. 1. Theory of Special Creation: . Conventional religious literature talks about the theory of special creation, according to which God, the supernatural being created the earth, light, plants and animals This theory has three suggested views: i. All living organisms (different species or types of plants & animals) that we see today were created as such The diversity of life forms was always the same since the time of creation & will remain the same in future also ii. ii. Earth is about 4000 years old All these ideas underwent drastic changes during 19th century when Charles Darwin showed that the existing life forms share similarities to varying degree among themselves and also with those life forms that existed millions of life ago Extinctions also took place during at different phase of geological history .

  7. Theory of Panspermial Cosmozoic theory: Some scientist believe that life has come on earth from other planets or outer space Early Greek philosophers thought units called 'spores' or pansperms' came on earth along with meteorites & they might have evolved into present day forms 2. .

  8. 3. It was also believed that living organisms (life) arose from decaying But Louis Pasteur demonstrated that life can arise only from pre- He showed that no life arose from the heat- killed yeast broth that Theory of Spontaneous Generation: matter like straw existing life. was kept in pre- sterilized closed flask, while new organisms arose from the heat- killed yeast that was kept in the flask left open in the air Wait Boil No growth 2 Wait Break neck Boil Microbial growth

  9. An experiment to demonstrate Spontaneous generation.. OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Covered jars Controlled Variables: ars, type of meat, location, temperature time Several days pass Manipulated Variables: gauze covering that keeps flies away from- meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur