It is very interesting to me that the 6,000 - 10,000 estimate of the age of the Earth, usually accomplished by counting generations, is an excellent estimate of how long civilization has been around--and the last we hear of Cain, at the end of Chapter 2 of Genesis, is that he "built the world's first city." Also, according to the Bible, his parents, Adam and Eve, were clearly created some (indeterminate) time after God created human beings: "man and woman" (at the end of Chapter 1).