An abstract of title is a record of a property’s ownership history; in the U.S., they typically start with the first transfer from the federal government or a colonial proprietor to a private owner, tracing it down to the date the abstract was prepared.
For example, the abstract for a house I once owned started with the General Land Office granting 200 acres to an ex-soldier under a bounty land claim in the 1840s, and then had every subsequent deed tracing the sale and subdivision down to the 50x150-foot city lot I purchased in 1989. Over the course of a century and a half, there were a couple of probate actions, including one when somebody died intestate, and a quiet-title action when somebody noticed a co-owner had mysteriously been dropped from a subsequent deed; the abstract of title included copies or extracts of every relevant record, including deeds, the probate judge’s orders, and portions of the wills.
I got the abstract (a bundle of papers) in conjunction with the purchase of title insurance; they actually precede the development of title insurance policies, and were a way of finding out if there were any flaws in the chain of title before you plunked down your cash. Basically, a trained researcher, often a lawyer, would go through the records in the courthouse, find and copy the relevant records, and render an opinion on the likelihood that somebody could challenge your ownership.
Over time, abstract and title companies tended to accumulate their own copies of the records in the courthouse, because it was easier to look them up in their own office than trot down to the county office. Also, if the purchaser after me had wanted an abstract, the office that prepared mine could have started with a copy of my abstract and confined their research to events and court filings after the date on which it was prepared. Moreover, the abstract of title for the house next to mine would have been identical for the first century, until the farmland was annexed to the city and divided into building lots, so the abstractor working on that property’s chain of title would have a century’s head-start if they had a copy of mine.
Even if your ancestor paid cash for the land 120 years ago, they might well have purchased an abstract of title. Even if they didn’t, an abstract company building up their own library of records might have acquired copies of the relevant paperwork, or have prepared an abstract for the previous owner that shows the ownership history prior to your ancestor’s purchase.
Anybody who cares long-term about who you worked for two decades ago probably has copies of the records. (For example, the Social Security Administration has the names and addresses of all of your employers who paid SocSec taxes on your earnings.) There aren’t many entities that care, however.
People care about land ownership, and so extra efforts tend to be made to preserve or recover records pertaining to that land.