Ancient Fossil Shells Show Levels of Mercury Dating Back to the Cretaceous Period

The outcome of an asteroid collision with Earth is commonly attributed to the mass extinction that killed off the majority of dinosaurs and approximately three-quarters of the planet’s vegetation and animal species about 66 million years ago.​

However, terrible volcanic eruptions in India may have also added to the annihilation process. Researchers had long argued the importance of the Deccan Traps eruptions, which began before the crash and lasted for about a million years, accented by the impact event.

Recently, a geochemical assay led by the University of Michigan of a fossil marine mollusk shells from all over the world is offering new data on both the climate reaction and environmental mercury contamination during the Deccan Traps volcanism.

High Mercury Levels

From the same shell type, the scientists discovered what seems to be a global signal of sudden ocean warming and uniquely increased mercury concentrations. Volcanoes are the most massive natural source of mercury traveling to the atmosphere. The study shows that the binary chemical signatures begin before the collision event and line up with the beginning of the Deccan Traps eruptions.

When the scientists put against the mercury levels from the ancient shells to aggregations of freshwater clam shells gathered at an actual site of industrial mercury pollution located in Virginia’s Shenandoah Valley, the levels were almost equal.

Proof from the research, which has been published on December 16th in the journal Nature Communications, endorses the theory that Deccan Traps volcanism had climatic and ecological effects that were significant, durable, and global, the experts conclude.

“For the first time, we can provide insights into the distinct climatic and environmental impacts of Deccan Traps volcanism by analyzing a single material,” said Kyle Meyer, lead author of the new study. “It was incredibly surprising to see that the exact same samples where marine temperatures showed an abrupt warming signal also exhibited the highest mercury concentrations and that these concentrations were of similar magnitude to a site of significant modern industrial mercury contamination.”

Meyer led the research as part of his doctoral dissertation in the U-M Department of Earth and Environmental Sciences. He is now a postdoctoral scientist at Portland State University.

Dating Back to the Cretaceous Period

Mercury is a toxic trace metal that is a health risk to humans, fish, and wildlife. Man-generated causes of mercury are coal-fired power plants, as well as artisanal gold mines. The place from which the researchers took freshwater clam shells, Virgina’s South River, warns people not to consume fish from the river.

“The modern site has a fishing ban for humans because of high mercury levels. So, imagine the environmental impact of having this level of mercury contamination globally for tens to hundreds of thousands of years,” said U-M geochemist and paper co-author Sierra Petersen.

The scientists theorized that the fossilized shells of mollusks, mainly bivalves like oysters and clams, could together show coastal marine temperature reactions, and different mercury signals inked with the release of significant amounts of carbon dioxide and mercury from the Deccan Traps.

The lasting Deccan Traps eruptions developed a vast area of western India and were dated back on the period of Cretaceous-Paleogene mass extinction, about 66 million years ago.

The research used fossil shells gathered from Antarctica, Argentina, India, Egypt, the United States, Libya, and Sweden. The experts assayed the isotopic composition of the shell carbonate to estimate marine temperatures, utilizing a recently created method known as carbonate clumped isotope paleothermometry.

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