When did the human life start?

There is, as yet, no definitive answer to this question.

Answer:

A lot of the answer depends on your definition of "Human". There were many hominid precursors to the human race so a timeline from Australopithecus and winding up with us would be:

• Australopithecus ramidus - 5 to 4 million years BCE
• Australopithecus afarensis - 4 to 2.7 million years BCE
• Australopithecus africanus - 3.0 to 2.0 million years BCE
• Australopithecus robustus - 2.2 to 1.0 million years BCE
• Homo habilis - 2.2 to 1.6 million years BCE
• Homo erectus - 2 to 0.4 million years BCE
• Homo sapiens - 400,000 to 200,000 years BCE
• Homo sapiens neandertalensis - 200,000 to 30,000 years BCE
• Homo sapiens sapiens - 130,000 years BCE to present

No effort was made to include the various archaic homo sapiens types, and homo neandertalis was inserted even though they were not linear ancestors of ours except for some cross breeding.