This cannot be established with absolute certainty, however it was many thousands of years B.C. The link below will give a fairly full story.
The Indus River valley
yellow river valley
Eurphates located in modern Iraq
Danube River Valley
The Nile River Valley.
In Nile River
The Ganges River valley
The earliest human settlements were little farming villages located in Mesopotamia, modern-day Iraq.
The Nile River
The Nile River
Harappan civilization develop in the Indus River valley
Mesopotamia