Bone is a living tissue made up of cells within a matrix of protein (mostly collagen) and minerals (mainly calcium and phosphorus).
The smooth compact bone found on all bone surfaces, and the spongy porous bone located between compact bone layers and in the ends of long bones, provide strength.
Within spongy bone and hollow shafts of long bones is marrow. It makes red blood cells to supply oxygen to our soft tissues, and white blood cells to fight germs or disease. It also stores and releases fat as we need energy.
How long can bones last? Hundreds of years, and even thousands of years under special circumstances. The chemical composition of bone — a combination of collagen and minerals — makes it strong and durable long after death. How well a bone is preserved depends on environmental influences and burial practices.