"why are we most likely to learn about the early history of the early by studying the rocs from the moon rather than those on the Earth ?"
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Question
How long have humans existed on Earth?
Human have existed for roughly half a million years, but this answer depends on the exact definition of "human". Fossil evidence shows that several human-like lineages developed during the past million years or so. >From fossils, the appearance of Homo sapiens is dated at about half a million years, and of anatomically modern Homo sapiens at about a hundred thousand years, values that are also supported by genomic evidence. Another data point, although not something you asked directly, is that the recent complete sequencing of the genome of the chimpanzee, which is the closest living relative of humans, suggests that chimps and humans diverged from their common ancestor about 6 million years ago. Of the many intermediate related species that have existed since then, only chimps and modern humans survive today. David Morrison
NAI Senior Scientist
June 12, 2006
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