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I've heard rumor that one day the population in the US will also regulate people to being cremated, there just won't be the land mass available to continue burying people.

In the UK, according to my old local vicar, after 100 years a grave could have the headstone removed and be reused, another vicar stated that if a grave is not visited or falls into disrepair, the same thing occurs.
Maybe time to dig Karl Marx up then in London. :-) (Highgate Cemetery, London)