When did life on earth first originate?
About 3 billion years ago.
The life of earth is supposed about 4.6 billion years. At that time water was in vapor. Water vapor took about 1 billion year for liquid form. In the anaerobic conditions, simple organic compounds are produced. These led to the origin of life by condensation of simple polymers into complex one.
Urey and Miller have proved it in the laboratory. Thank you