The literal/historical view of Genesis (that the six days in creation week are ordinary days and the genealogies in chapters 5 and 10 really do trace back to Adam just thousands of years ago) is based on centuries of sound biblical interpretation and history. The Pharisees at the time of Christ held to this position (unwaveringly). Jesus regarded Genesis as historical each of the 42 times He referenced the Old Testament. The Hebrew word for day (yom) always means an ordinary day when used with ‘evening,’ ‘morning,’ or a number (like yom is used for bracketing each of the six days of creation in Genesis 1).
Did God mince his words when he said (in the 4th commandment no less) that He created the heavens and the earth to sea and everything in them in six days (Exodus 20:11)[i]. Did he want the receiver of this communication to believe anything but six ordinary days when he spoke it in context of the Sabbath which is a real day? On Day Four God further showed that these were literal days by telling us the purpose for which He created the sun, moon, and stars—so we could tell time: literal years, literal seasons, and literal days.
The list could go on and on for the reasons to scripturally support that the days in the creation week account were ordinary and the Genesis genealogies add up to thousands (not millions) of years.
[i] Another confirmation is the conjunction of the word work and day twice in Genesis 2:2 “on the seventh ‘day’ God ended his “work” which he had made; and he rested on the seventh “day” from all his “work” which he had made (confirming that Day 7 was a “work day” like in Exodus 20:11).
See the Age of the Earth FAQ for a more extensive discussion on the “Days of Creation.”