Can human bones and/or teeth which have lain buried in the earth for several years become discolored from their time in their environment?
This is to find out to what extent discoloration of the human skeleton and human bones can be used to establish how long a skeleton may have been buried.
Bones and teeth are among the last parts of a corpse to undergo decay, so they may lie in contact with vegetation and/or soil for a considerable length of time. During that time, fungi and environmental acids can act on bone to break it down and increase its porosity, and various minerals in the soil can migrate into the bone in an ion-exchange process that replaces the calcium that is leaching out. A forensic scientist with a good grasp of the minerals present in local soils can use this information to make an estimate of how long bones have been buried. By contrast, bones that are exposed at the surface of the soil tend to become bleached white by the sun, and in this case calcium that leaches away is not replaced by other minerals, so bones that are on top of the soil do not stain as readily. In this case the loss of calcium and the bleaching effects can be used for time estimates.
If you have access to a subscription service such as Ebsco, this is a really interesting article with a lot of details about how the calculations are done. If not, the link will take you to the abstract, which is also worth a look.