Cambrian trilobites as archives for Anthropocene biomarkers and other chemical compounds

Abstract

Abstract This study examined well-preserved trilobite fossils from the middle-Cambrian (∼507 million years ago) Wheeler Shale of Utah to determine the proportion of original marine biomarkers compared to later chemical overprints. Using a technique to characterize multiple biomarkers simultaneously, the fossils revealed more about modern terrestrial ecosystems and anthropogenic influence than they did about early Paleozoic oceans. Plasticizers, flame retardants, petroleum byproducts, and insect repellent comprised up to 96% of all compounds present in the trilobite exoskeletons, whereas the rest included biomarkers indicating algae, vascular plants (e.g., conifers), and biomass burning inputs. Importantly, contamination occurred despite measures taken to minimize it, highlighting the pervasiveness of anthropogenic contaminants in fossils. These compounds provide invaluable data concerning regional anthropogenic alteration, even though scientific papers usually do not report the types and diversity of contaminants. Scientists must therefore record the composition and amounts of these chemical contaminants because the potential for overprinting could also bias other geochemical measurements, such as stable carbon isotopes, highlighting the need to constrain the sources of contamination within samples. Although the middle Cambrian fossils appear to be excellently preserved, their chemical composition is mainly an Anthropocene overprint.