Ancient biomolecules: their origins, fossilization, and role in revealing the history of life

The discovery of traces of a blood meal in the abdomen of a 50-million-year-old mosquito reminds us of the insights that the chemistry of fossils can provide. Ancient DNA is the best known fossil molecule. It is less well known that new fossil targets and a growing database of ancient gene sequences are paralleled by discoveries on other classes of organic molecules. New analytical tools, such as the synchrotron, reveal traces of the original composition of arthropod cuticles that are more than 400 my old. Pigments such as melanin are readily fossilized, surviving virtually unaltered for ~200 my. Other biomarkers provide evidence of microbial processes in ancient sediments, and have been used to reveal the presence of demosponges, for example, more than 635 mya, long before their spicules appear in the fossil record. Ancient biomolecules are a powerful complement to fossil remains in revealing the history of life. Ancient biomolecules range from hundreds of thousand-year-old DNA to lipids and structural macromolecules that survive for billions of years. Extracted from fossils and sedimentary rocks, they reveal organism relationships, past environments, and the origin of fossil fuels. In the oldest rocks they may be the only evidence of particular life forms.