Earth dating systems
At its core, that date—any date really—is just a code.
Into this calendar chaos, a humble monk by the name of Dionysius Exiguus stepped in. Surely we can find a better event to start counting from.
(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.
See the Isochron Dating FAQ or Faure (1986, chapter 18) for technical detail.
A young-Earther would object to all of the "assumptions" listed above.This causes the data points to separate from each other.