Why do we have "weeks"?

[Big Limpin']

The time for the earth to spin once is called a "day"
The time for a moon phase is called a "month" (originally)
The time for earths axis to cycle is called a "year".
So where do weeks come from?

The only thing i can think is the bible (on the 7th day...). That i hate religion has nothing to do with this though. It just strikes me as odd that we chose to make 7 days as some kind of cycle. Works weeks, etc.

Far in the future (more than decades), how possible is it that "weeks" will cease to exist?