Answer: Minerals
Explanation: The body decomposes and after about 40 to 50 years bones are mostly brittle and dry with no traces of flesh. After thousands of years bones also disintegrate (decay) leaving brittle mineral frame. The life of bones is determined by the soil type its buried in, nuetral soils takes longer then acidic soil condition.
In this case osteocytes(bone cells) are the first to decompose followed by the cartilage and bone marrow, leaving behind mineral traces that scientist can study after thousand years.