And for a follow-up, I'd like to ask as well: what would be the most logical, nature based (as opposed to religion based) point in time to pick as a new zero-point, if humanity decided to start a new timeline?
It would have to be recent enough that we know exactly what year it happened (so not the extinction of the dinosaurs), but far enough back in time that most of history would happen "after zero" (so not, say, the eruption of Krakatoa).
To quote our u/DanKensington, "The Christian BC/AD calendar is just one amongst many possible systems of year counting". In this thread that user has linked to the useful FAQ, and u/MichaelJTaylorPhD writes a summary on how dates were counted in Greco-Roman times, noting that "eponymous years" after reigning magistrates were rather common. If you want to read more about that period and region there are also this by u/Iphikrates, this by u/KiwiHellenist and this by u/toldinstone, and u/Welfontheshelf has discussed Byzantine calendars here. There is also this thread by u/voorface on Chinese calendars. Further answers are of course appreciated, there are probably many more calnedar-systems I am not aware of!