Inherit the Stars — James P. Hogan

The man on the moon was dead. They called him Charlie. He had big eyes, abundant body hair, and fairly long nostrils. His skeletal body was found clad in a bright red spacesuit, hidden in a rocky grave. They didn't know who he was, how he got there, or what had killed him. All they knew was that his corpse was fifty thousand years old -- and that meant this man had somehow lived long before he ever could have existed.