Contaminants accumulate.

The resulting material is a complex mixture of original biological compounds and diagenetic products that must be separated, characterized, and selectively dated.

The two protein fractions that researchers used for the Arlington Springs bone were collagen and osteocalcin.

Collagen is the most abundant protein in bone — the structural framework that, when mineralized by calcium phosphate crystals, gives bone its strength.

It is a large, stable protein that, under favorable conditions, can survive in chemically recognizable form for tens of thousands of years.