According to the widely accepted scientific account, the universe erupted 15
billion years ago in an explosion called the ' Big Bang' and has been expanding and cooling ever since. Later there gradually emerged the conditions necessary for the formation
of atoms, still later the condensation of galaxies and stars, and about 10 billion years
later the formation of planets. In our own solar system and on earth (formed about 4.5 billion years ago), the conditions have been favorable to the emergence of life.

While there is little consensus among
scientists about how the origin of this first microscopic life is to be
explained, there is general agreement among them that the first organism dwelt
on this planet about 3.5–4 billion years ago. Since it has been demonstrated
that all living organisms on earth are genetically related, it is virtually certain that
all living organisms have descended from this first organism. Converging
evidence from many studies in the physical and biological sciences furnishes
mounting support for some theory of evolution to account for the development and
diversification of life on earth, while controversy continues over the pace and
mechanisms of evolution. [6]