I was playing around with outlook to see if i could use it as a testbed for spanoflife stuff (since it already has a nice built in data model and API for dealing with dates, events, and tasks), and I entered an appointment for Feb 2, 1874 just to see if it could handle dates far in the past. It accepted it and promptly put up a message telling me my appointment was 6714 weeks overdue.
In fact, through exhaustive study, the earliest date you can enter is 4/1/1601. An odd starting point, maybe someone has a sense of humor.
As always, Wikipedia astounds, with a page dedicated to 1601:
I think I will have to scrape or link to Wikipedia for this kind of event content.
This does bring up a point about date handling. I want to be able to represent the entire lifespan of the earth on a timeline, which of course is only fuzzily known. I have entries in the tables for start and stop times, but those are going to have to be supplanted by "approximate" dates of some kind. I want to use the modern calendar, obviously, but it has to be able to zoom out to things like "10,000 years ago".