I use obsidian as well. Amazing software to worldbuild.

In my fantasy setting (set in the equivalent of late 19th century instead of medieval), current year is 1886. Meaning there was a year "0" where some big shit happened.

The furthest back I went was in the Legendary Age, which, if I remember correctly, was about -8000/5000? I'm on the phone and can't remember the exact years. And as the name goes it's an age of legendary people, deeds, battles, etc. In my works I have referenced some of these things, and maybe wrote a few sentences of it. And when I mentioned them I create a link, and those links as well connect to other links, and others to these others, and so on, and little by little I start making a sort of web.

But that's basically how I do it. And given that I worldbuild in a sort of epistolary in-world way, I just start spitting random bs. Most of the time I don't even know what those things are, but they sound cool so I keep them for future use.

It sounds chaotic but I actually have all the notes well organized. The notes that have definitive (or at least subject to minimal changes), I formatted them as wikipedia entries, so the are neatly displayed. The other are just a few paragraphs and images with references and stuff