Answer:
Step-by-step explanation:
When earth came into existence, it was very hot. The earth has no atmosphere. The environment of the earth was not suitable for the lives. There was no water, oxygen, which was needed for life. The earth was filled with ammonia, carbon dioxide, water vapor, and methane gas. Gradually the water vapor splits and forms oxygen and hydrogen. The oxygen atoms again combine with oxygen atoms from the ozone layer and the earth's atmosphere. The water vapors start cooling and start raining. Also, the splitting oxygen atoms combine with methane and ammonia and produce water. The raining in the earth had been going on till the earth got cool down. Thus the larger holes of the earth were filled with water and formed the ocean. After the formation of the ocean, life came to existence. The first organism was a unicellular organism lived in the ocean. By the process of evolution, many complex organisms were crowded on the earth. Thus the earth atmosphere became suitable for life.