Introduction

Evolutionary biology –

               The study of life forms on earth is known as evolutionary biology.

• The process of gradual modification of simpler forms into the present complex forms over millions of years is called evolution.

    Origin of universe

• The universe is almost 20 billion years old.
• Huge clusters of galaxies comprise the universe.
• Galaxies contain stars and clouds of gas and dust.
• A scientific theory called big bang theory explains that, the unimaginable large explosion created the universe.
• As the universe expanded and cooled, the temperature came down and materials condensed under the influence of gravitation to form present day galaxy.

Big bang theory 

According to it a huge , explosion occurred , the universe expanded , temperature came down and hydrogen and helium were formed later. The galaxies then were formed due to condensation of gases under gravitation.

ORIGIN OF EARTH

• Our galaxy is called milky way formed 4.5 billion years back.
• There was no atmosphere on early earth.
• Water vapour, methane, carbon dioxide and ammonia released from molten mass covered the surface.
• The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2.
• Oxygen combined with ammonia and methane to form water co2 and others.
• The ozone layer was formed, as it cooled, the water vapor fell as rain, fill all the depressions and form oceans.

THEORIES OF ORIGIN OF LIFE 

• Life appeared 500 million years after the formation of earth, i.e, almost billion years back.
• Different scientists had put different views about the origin of life.
• THOERY OF SPECIAL CREATION:- According to this theory god created life by his divine act of creation.
• THOERY OF PANSPERMIA /COSMOZOIC THEORY :- According to early greek thinkers, unit of life called spores or panspermia came from outer space and developed into living forms.
• THOERY OF SPONTANEOUS GENERATION:- According to this theory , life originated from decaying and rotting matters like straw , mud etc.

NOTE 

• Louis pasteur dismissed the theory of spontaneous generation and demonstrated that life came from pre existing life.
• He placed killed yeast in pre-sterilized flask and another flask open to air . he showed that life did not originate in the former but new living organisms arose in the latter flask.

Theory of chemical evolution or oparin haldane theory

This theory was given by oparin and haldane and stated that life originated from pre existing non living organize molecule (eg:- RNA, Protein etc)

The conditions on earth favouring chemical evolution were high temperature, volcanic storms, reducing atmosphere containing CH3 etc.

Experimental evidence of chemical evolution miller’s experiment.

• In 1953 , Stanley miller and harold urey tested the oparin-haldane hypothesis using the condition of pre-biotic earth.
• Experimental set up- in a closed flask containing CH3, H2, NH3 and water vapor at 800’ c.
• Electrical discharge was created.
• The condition were similar to those in primitive atmosphere.

Observations-

After a week they observations presence of amino acid complex molecules like sugars nitrogen pigments and fats in the flask.

Conclusions- 

1. It provides experimental evidence for the theory of chemical origin.
2. It shower that the first non- cellular biomolecules exist in the form of DNA, RNS, Polysaccharides. And protein.

Formation of first cell-

• First non- cellular life forms originated 3 millions years ago.
• These could be giant molecules like RNA,protein and Polysaccharides. And protein.
• First cellular form of life originated about 2000 million year ago.
• These might have been single cell formed in aquatic environment.