ORIGIN OF LIFE

• 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.
• 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, to fill all the depressions and form oceans.
• Life appeared 500 million years after the formation of earth, i.e., almost four billion years back.
• Different scientists had put different views about the origin of life.

Fig. early earth  

Fig. Milky way