Although embalming is not required by law it is performed on a large percentage of bodies that will be buried. From this point on, nature is very efficient at breaking down human corpses. Decomposition is well under way by the time burial or cremation occurs. However, the exact rate of decomposition depends to some extent on environmental conditions. Decomposition in the air is twice as fast as when the body is under water and four times as fast as underground. Corpses are preserved longer when buried deeper, as long as the ground isn't waterlogged.
The whole process is generally slower in a coffin, and the body may remain identifiable for many months. Some tissues, such as tendons and ligaments, are more resistant to decomposition, while the uterus and prostate glands may last several months. But within a year all that is usually left is the skeleton and teeth, with traces of the tissues on them - it takes 40 to 50 years for the bones to become dry and brittle in a coffin. In soil of neutral acidity, bones may last for hundreds of years, while acid peaty soil gradually dissolves the bones.
Abraham Lincoln was embalmed after his assassination in 1865. In order to prevent anyone stealing Lincoln's body, Lincoln's eldest son Robert called for Lincoln's exhumation in 1901 to be buried in a concrete vault in the burial room of his tomb in Springfield, Illinois. Fearing that his body would have been stolen in the interim, Lincoln's coffin was opened, and his features were still recognizable, thirty-six years after his death.
Rosalia Lombardo, who died at age two on 6 December 1920 and was one of the last corpses to make it to the Capuchin catacombs of Palermo, Sicily before the local authorities banned the practice. Nicknamed the 'Sleeping Beauty', Rosalia's body is still perfectly intact. Embalmed by a certain Alfredo Salafia, she is in a glass case, looking very much like a surreal doll.
https://en.wikipedia.org/wiki/Embalming#Notable_embalmings
http://www.bbc.com/future/story/20150508-what-happens-after-we-die
