When did humans start to keep track of years with unique identifiers for each year?
I assume that the realization that seasons were cyclic came first, and that at some point we decided to call each cycle a year (I assume this happened before the discovery of how the solar system worked, since it's easier to notice season cycles than rotations around the sun). I assume it was at some later point that we decided to give each of those years a unique identifier (e.g. number) to help keep track of things.
My questions is: when was that "later point"? When did we start "numbering" the years to keep track of them? Who did it first? How did they do it (arbitrary number, years since notable event, ..?)
Also, when did a large portion of a population become aware of this (the numbering)? i.e. if you ask pretty much anybody today they'll be able to tell you what year it is, no matter their walks of life. But I guess that when people first started numbering years it was most useful to certain members of the population and inconsequential for others, therefore some people might have been unaffected and unaware of the current year.