Only the well-purified collagen represents the original biological carbon of the Arlington Springs individual with sufficient reliability to anchor the age determination.

The amino acid analysis that Johnson, Stafford, and colleagues applied to the collagen fraction was the verification step: by checking the specific amino acids present and their relative proportions, researchers could assess whether the extracted collagen was genuine ancient protein or a contaminated or diagenetically altered material.

Ancient collagen that has been preserved without extensive alteration has characteristic amino acid proportions that differ from degraded or contaminated products.

The Arlington Springs collagen passed this test, supporting the use of its radiocarbon date as the best estimate of the individual’s age.