I'm assuming the seven day week originated in Europe, but when and how did this happen, and how did it spread? Did the rest of the world have a concept of a week, in places like Mexico or India or Egypt?
More can be written, but you might be interested in some of the discussions in the "Weeks, weekdays, and weekends" section of the Calendars AskHistorians wiki page.
This is not to discourage discussion. More questions, data, and debate are welcome.