Hebrew years 120 to 240 (3640-3520 BCE)
There is no detailed chronology of Cain’s descendants in the Biblical text, as if they were not people worthy of mention. We only learn that he settled down to build the first city:And Cain knew his wife, and she conceived and bore Enoch. He became a city builder and he named the city after his son Enoch.
--- Genesis 4:17
Archaeology shows that one of the earliest cities in the world was Uruk, which is located in what is now Iraq. The story of the Bible is not dissimilar to what we have learned from civilization which was first composed of wandering hunters who later turned into sedentary farmers. The same was followed by Cain.
In the oldest Babylonian language, Sumerian, Uruk was known as Unug, which is close enough to the Biblical name of Enoch, considering that these languages do not put much emphasis on vowels. The early settlement of Uruk was to be built over. One of the greatest builders of the city was called Enmerkar who is commonly associated with Biblical king Nimrod. Uruk then became the largest city of these times and was later ruled by the semi-mythical king Gilgamesh.
Sumer was a region located between the two big rivers south in Southern Mesopotamia. It was a fertile region that saw other city-states being built over time.
Sumer and its first city states
On Adam’s side, his wife Eve finally conceived again and bore another son, Seth, born in Hebrew year 130. It is said that, after the Original Sin and the murder of Abel by his brother Cain, Adam started to have doubts about the future of humanity and refrained from having any intercourse with his wife. He became pious. Only after 130 years, he understood that the Creation must continue and he fathered Seth at his image. This is nearly the same expression used by the text when God created Adam, so it shows that the birth of Seth was with the right spirit from Adam:And Adam lived a hundred and thirty years, and begot a son in his own likeness, after his image; and called his name Seth.--- Genesis 5:3
The expression, for the creation of Adam, is slightly different:
And God said: 'Let us make man in our image, after our likeness.--- Genesis 1:26
The difference is that, in the creation of Adam, the emphasis is on the identical image, whereas in the creation of Seth it is on the likeness. It ought to be different because in th first instance it is God Himself who created Adam and Adam was in a state of perfection, before the sin. In the creation of Seth, there was prior sin, atonement, and then purity can happen again. So Seth could, at best, be after the image of Adam, but not in his image.
Before the end of the second generation, in year 235, Seth also had a son he named Enosh, a name which is close enough to Cain’s son, Enoch. Both Enosh and Enoch lived in the same period of time, and followed the same path, turning away from God and even forbidding to mention Him:And as for Seth, he too had a son; he called him Enosh; at that time, it was profaned to call the name of God.
--- Genesis 4:26
In Genesis 1:26, God decided to make man in His image; and in Genesis 4:26, men decided to make gods in their image: this is what is meant by the text it was profaned to call the name of God. The God of the Creation, the One that Adam and Eve feared most, was being "rejected" by mankind. The parallel of the number 26 for these two verses is striking, because 26 is known to be the numerical value of God's 4-letter name (YHVH= 10+5+6+5= 26).
The Hebrew alphabet and its numerical values
This generation, called the generation of Enosh, which was first to introduce idolatry in mankind, was used as a reference of bad human behaviour in later years:
R. Hiyya b. Abba said in R. Johanan's name: He who observes the Sabbath according to its laws, even if he practises idolatry like the generation of Enosh, is forgiven. --- Talmud, Shabbat, 118b
 The name Iraq was in fact chosen after the name Uruk; the ruins of the city are located at the following coordinates on Google Earth: 31°19'30" N 45°38'10" E