Fossil shells show that levels of mercury increased before the dinosaur extinction

By performing a geochemical analysis of marine shellfish fossils from different parts of the world, scientists at the University of Michigan have obtained new information on how much and how mercury has contaminated the world in the past. They also obtained information on global warming levels at the time of the extinction of the dinosaurs just over 65 million years ago.

During this period, there seems to have been abrupt warming of the ocean and a high level of mercury concentration. The latter in particular should have been caused by strong volcanic events as volcanoes themselves are the largest natural source of mercury that ends up in the atmosphere. Scientists believe that the increase of mercury in the environment during this period occurred due to the volcanic phenomena of the so-called Deccan Traps, an igneous area now belonging to India known as one of the largest volcanic areas in the world.

These conditions occurred before the impact of the Chicxulub asteroid, which decreed the end of the dinosaurs themselves, as well as many other life forms. These same conditions, therefore, according to this study, would have made the level of mass extinction in this period even more serious and would have favored the extinction of the dinosaurs.

The study, published today in Nature Communications, describes how scientists themselves have used to compare the mercury levels of these ancient shells with those examined in today’s freshwater shells collected in particular at a site known to be affected by industrial mercury pollution, the Shenandoah Valley, Virginia. The researchers found that the levels were more or less the same.

The study, therefore, supports the idea that the volcanism of the Deccan Traps had a profound impact on the climate and in general also on world ecology, lasting impacts as Kyle Meyer, lead author of the study, says: “For the first time, we can provide information on the distinct climatic and environmental impacts of Deccan’s volcanism by analyzing a single material. It was incredibly surprising to see that the same identical samples where marine temperatures showed a sudden warming signal also showed the highest concentrations of mercury and that these concentrations were similar in magnitude to a site of significant modern industrial mercury contamination.”

This is not the first time that traces of mercury from the past have been analyzed to understand concentration levels at various times, but it is the first time, as Sierra Petersen, another author of the study, specifies, that these levels are analyzed by studying fossil shells. This new technique could, among other things, be used for other studies in the future to analyze other mass extinctions and their relationship to possible climatic disturbances or natural phenomena.