500 years ago, the mountain dwelling Carac clan was cursed with undeath: whenever they or any of their descendants die, their corpses rise as undead creatures, or if burned, as shadowy specters. The Carac quickly adopted a custom of casting their deceased into a chasm. This does not prevent the occurrence of undeath, but nothing has ever crawled back out of the hole so it's always been considered a wise solution.
I would like to know approximately how many undead creatures are in this chasm. I know there are resources online for how to estimate the length of a generation etc., but I'm a complete blockhead at this sort of thing and can't figure out for the life of me how to calculate the number of people who have ever died in the Carac clan.
In the mountain valley the Carac call home, let's say the clan has had a stable population of 1000 for the last 500 years. Not a realistic assumption, but I'm only trying to figure out how many undead might plausibly occupy the chasm, not an exact figure. I'm sure there are other figures you will need from me to answer this question: please feel free to make any other demographic assumptions that you wish for an iron age barbaric mountain folk, or ask in comments and I'll try to respond promptly.