500million years ago earth was a dry planet without no living gases or moisture in its's atmosphere used to contain lot  HCl.  after lot of collisions of comets meteriods with earth an un even surface is formed on it. later  volcanic eruptions an other disasters moisture formed in atmosphere. slowly rains were started but they are acidic rains. later due to water cycle process water and atmosphere are purified and developed. plants and other creatures are formed.this is the story about the evolution of the earth
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