>>40527036 (OP)The earth's land surface is 148,940,000 Square Kilometers = 148,940,000,000,000 Square Meters.
There are approximately 109 billion people who have died throughout human history. Let's round those numbers to 150 trillion sq m and 100 billion dead people, and we'll say it takes 2 sq m of land to bury a person. That means that about 200,000,000,000 sq m of land are graves. 200 billion is ~0.13% of 150 trillion.
If graves were evenly distributed, a small town- let's say 50 sq km or 50,000,000 sq m- would need a graveyard about 65,000 sq m, a square of roughly 255 meters on a side. That doesn't seem too unreasonable.
But of course, graves aren't evenly distributed- just like human populations, they're concentrated in certain areas and absent from others. On the other hand, not everyone is buried- lots of people have been cremated, or lost at sea, or eaten by scavengers. And even when people are buried, graves don't necessarily last forever- depending on climate, moisture, soil conditions, etc, bodies, including bones, can break down and decay, while tombstones can erode away or be stolen and re-used in construction. Eventually the site of a burial can become indistinguishable from any other patch of ground. And if that doesn't happen fast enough, it's pretty common for large cities to clear room in graveyards by digging up old bones and storing them somewhere else- that's what the famous Paris Catacombs are for, for instance.