Question

what is big bang theory 

Answer 1

The theory says that the universe has the beginning at the time of big bang.It's the oldest known radiation that scientists have detected.The first stars were formed after 400 million years after big bang.
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Answer 2

Answer:

The Big Bang theory was proposed to explain the origin of universe. According to this theory, the origin of universe took place due to a single huge explosion in the space due to which the various galaxies were formed in it.

Its various postulates were :

• The earth formed about 4.5 billion years back.
• There was no atmosphere on early earth.
• Water vapour, methane, carbon dioxide and ammonia were released from the molten mass which came out of earth due to volcanic eruptions.
• The UV rays broke up water into Hydrogen and Oxygen.
• The ozone layer formed from oxygen slowly
• Water vapour condensed fell down as rain, to fill the depressions and form oceans.