In a geological context, a biomarker is an organic compound or chemical that can be unambiguously traced back to specific molecules made by living organisms. Organic molecules in animals are broken down during fossilization, owing to the stresses of increased temperature and pressure; however, some such molecules break down along specific pathways that eventually result in resistant altered molecules (geomolecules). These geomolecules preserve, essentially, the chemical skeleton of the original molecule and therefore allow its presence in a fossil to be accurately determined.