The world was created by God nearly six thousand years ago, as we shall set forth in the course of this book; although those who have entered upon and published a calculation of the dates, but little agree among themselves. As, however, this disagreement is due either to the will of God or to the fault of antiquity, it ought not to be a matter of censure. After the formation of the world man was created, the male being named Adam, and the female Eve. Having been placed in Paradise, they ate of the tree from which they were interdicted, and therefore were cast forth as exiles into our earth. To them were born Cain and Abel; but Cain, being an impious man, slew his brother.
He had a son called Enoch, by whom a city was first built, and was called after the name of its founder. From him Irad, and from him again Maüiahel was descended. He had a son called Mathusalam, and he, in turn, begot Lamech, by whom a young man is said to have been slain, without, however, the name of the slain man being mentioned— a fact which is thought by the wise to have presaged a future mystery. Adam, then, after the death of his younger son, begot another son called Seth, when he was now two hundred and thirty years old: he lived altogether eight hundred and thirty years.
Seth begot Enos, Enos Cainan, Cainan Malaleel, Malaleel Jared, and Jared Enoch, who on account of his righteousness is said to have been translated by God. His son was called Mathusalam who begot Lamech; from whom Noah was descended, remarkable for his righteousness, and above all other mortals dear and acceptable to God. When by this time the human race had increased to a great multitude, certain angels, whose habitation was in heaven, were captivated by the appearance of some beautiful virgins, and cherished illicit desires after them, so much so, that falling beneath their own proper nature and origin, they left the higher regions of which they were inhabitants, and allied themselves in earthly marriages.
These angels gradually spreading wicked habits, corrupted the human family, and from their alliance giants are said to have sprung, for the mixture with them of beings of a different nature, as a matter of course, gave birth to monsters.
Source: Sacred History (New Advent)