Collagen in cortical bone is the protein scaffold that, when mineralized with calcium hydroxyapatite crystals, gives bone its distinctive mechanical properties.

In living bone, collagen makes up roughly 20 to 30 percent of the wet mass of cortical bone.

Over thousands of years, collagen degrades — but under favorable preservation conditions, recognizable collagen can survive for tens of thousands of years.

The XAD purification method used at Arlington Springs addresses the most significant chemical challenge in ancient bone dating: the contamination of preserved collagen with humic acids.

Humic acids are the complex organic molecules produced by the decomposition of plant and animal matter in soil.