What Happens to a Buried Body After 10, 50 and 100 Years

Depends entirely on the conditions under which the body is buried and environmental conditions to where it is buried.

If a person is buried in a modern, high quality casket, compete with the additional concrete "grave vault" and the body has been treated with standard embalming techniques, it can remain pretty much intact for a very long time. Many became rather "mummified" with the moisture contact gradually evaporating.