I imagine the concept of the 7 day week comes from "God" creating reality in 6 days and resting on the 7th (Sunday). Was there a concept of a "week" before this time and how was it different?
Also, we name the days of the week after ancient deities (Saturnday, Moonday, Odinsday etc) - does this suggest there was a more ancient concept of a repeating day system (or "week" to use laymans terms)
More can be written on the subject, but you might like to look at the "Calendars and timekeeping" FAQ page, in the section "Weeks, weekdays, and weekends" (in the app, the "#" anchor doesn't work, so find it in the middle of the page). For the Babylonian evidence adduced by /u/Nejfelt, you might like the one on "fortnight", with some information on the connection between 14 days versus 7 days and 28ish days in a lunar cycle.
This is not to discourage discussion. Questions, data, and debate are always welcome.
Just a point of correction; the 7th Day in the Biblical week is Saturday, which is still observed by Jews (and some Christians) as the Sabbath.