Existence of life on Earth

There are two suppositions/ideas/speculations about the origination/creation of life on earth. The I st/first of these is that the earth was very flaming/hot in the origination/development/beginning, as was the sun itself. Gradually, it cooled down. In the operation/procedure/process of cooling down, it give birth to life by chance.

 No one can say how when or why it occurred/arise/happened. It established/begin/started in the kind/form of simple organisms who could reproduce themselves. From these simple starting/origination/beginnings came a stream of life which develop/grow more and more complex.

Ultimately, came the last/end/final product of this series/chain of life--the human beings. The other suppositions/speculation/ideas is that life came into existence/being as a result of another accident. Atoms found in living organisms (Carbon, oxygen, hydrogen, nitrogen etc.) got mix-up/unite/merge/fuse/unified by chance and gave birth to life.

Anyhow, no one can give a clear motive/thought/idea how life on earth came into being/existence.