Dating systems history
The first two parts—the month and date—have had a legion of originators, from Cro-Magnon astronomers marking phases of the moon on their eagle bones, to Mayan mystics tracking the movements of the stars from their forest canopies. Tests date the Earth to about 4.54 billion years old, but a whole lot of that time didn't really have anything of substance—to us humans, at least.
The 365-and-change-day calendar we use is the result of scientific sweat, an attempt to bring us to a Verifiable Truth regarding how long it takes the Earth to complete one rotation around the sun. Starting a calendar 4.54 billion years ago doesn't make much intuitive sense.
Some simply appeal to arguments of tradition and familiarity with the system.
They see the system as an attempt to eliminate “Christ” from the calendar, just as many reject the expression “x-mas” for removing “Christ” from Christmas.
(Let's not even discuss Year Zero, seeing as this jockeying for Year One position occurred before the concept of zero had even been invented.) If we wanted to allow for commerce, trade, and simple communication across cultures to develop, we needed to be living in the same year. The Byzantine Empire started its first year in what was considered the year of creation (our 5509 B. The Church of Alexandria began its Year One in what is now 284 A. And two, when most people see it, they think it stands for Christian Era and Before Christian Era, so it doesn't really solve the problem people wanted to solve.” As the world continued to “shrink” due to the establishment of trade routes and expansion of population and as once-insular communities started opening up and exploring, a single Year One would have inevitably dominated.
The Greeks were among the first to try to get everyone running on the same year. D., to coincide with the rise of Roman emperor Diocletian into power. C.—that is, “before Christ”—wasn't introduced until 1627, by a French astronomer. D., so decided to figure that in by counting backwards. The specifics of which one are not particularly important.
As former UN General Secretary Kofi Annan put it in a statement marking the turn of the millennium: The Christian calendar no longer belongs exclusively to Christians.' For some, these are fighting words: the Southern Baptist Convention resolved, also in 2000, to resist the 'revisionism' implicit in the CE/BCEsystem and to retain AD 'as a reminder to those in this secular age ... The AD/BC chronology is not so ancient as some proponents suppose; nor is the CE/BCE system so recent.
For the first five centuries of their religion, Christians marked time according to local conventions, usually from the legendary foundation of Rome (753 BC), or from the Diocletian reforms (284 AD).
According to these systems, we count time backwards Before the Common Era (B.