The condition on earth billions of years ago.

Billions of years ago Earth was just a planet made out of rocks. After the Big Bang Theory, Earth was being formed. After it was formed it took years and years for life to even start on earth. What started life was when Earth started to produce it's own water then soon it made volcanoes which made islands which formed into gigantic places that we call home. Later on Earth started to produce it's own weather and atmosphere. As earth had it's first rainfall, the ground started to grow green leaves that we call grass and trees. With those changes, life was starting to be born. The first living things on Earth, singled-celled micro-organisms  or microbes lacking a cell nucleus or cell membrane known as prokarotes. Later on the the organisms starting producing more organism which evolved later into human and animal life.

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Dna overload will occur

They formed the oceans.  as they melted water was formed and the water made the oceans