Question

How long has life existed on earth?

Answer 1

3.5 billion years

Explanation:

Although earth is approximately 4.55 billion years old, the oldest known fossils are nearly 3.5 billion years old, but some scientists have discovered chemical evidence suggesting that life may have begun even earlier, nearly 4 billion years ago (Reference: pbs. http://www.pbs.org/wgbh/evolution/library/faq/cat06.html)