When did man first walk on earth?

Note: This question was originally placed in the Science category and generated both science and religion based responses. Subsequently, the original poster reiterated his desire that the question be answered in a scientific rather than a religious context. Quote: I put it in here, because I want a scientific answer. Unquote

Considering the fact that this question was placed in the Science and Environment FAQs rather than in the Religion and Spirituality FAQs, an appropriate response would be that "hominoids," which belong to the Hominoidea super-family of primates and include apes and humans, are thought to have first walked on earth around 6 million years ago.

For those who are looking for an answer based on religious teachings, please see related questions in those categories.