I've been very curious lately as to where our time scale comes from, what it was truly based on, who started using that scale, and how it spread to apparently becoming globally accepted? If the time scale was supposedly based on the year of Christ's birth, why did other countries, predominated by other religions, also start using it? How, if at all, has it evolved over the centuries, and is it as practical as most of us view it?
You may be interested in this section of the FAQ.
You may be interested in the Calenders and Timekeeping section of our FAQ, particularly the subsection on How did the world agree on what year it is?