CSI Dino: Death by Mercury Poisoning?

Figure 1: Incorporation of mercury from Deccan Volcanism into dinosaurs, Part 1. (Image credit Lim Jia Yi Annabel)
Figure 2: Incorporation of mercury from Deccan Volcanism into dinosaurs, Part 2. (Image credit Lim Jia Yi Annabel)

Scientists are getting an exciting glimpse into the extinction of the dinosaurs… by looking at fossilised shells belonging to mussels, clams, and the like. That’s unusual enough already, but the story these ancient molluscs are telling is also one you might not suspect.

The fossil record informs us that dinosaurs died 66 million years ago (Mya). That coincides with the collision of a terrifying meteorite with the Earth. What most people don’t know is that 66 Mya is in the ballpark of a separate devastating event as well—intense volcanic eruptions spanning ~750,000 years, spewing tons of hot basalt which eventually formed the Deccan Traps.

From the extent of the eruptions, it’s no stretch to assume that massive amounts of volcanic gases were being emitted too. Temperature-raising CO2 is one of them, and toxic mercury is another. But with no proof of the biological incorporation of said mercury from the atmosphere, it was impossible for scientists to definitively conclude whether it had any effect on the fauna at that time… until now.

Using cold vapour atomic fluorescence spectroscopy (CV-AFS), scientists were able to calculate mercury concentrations within mollusc specimens. The results suggested that the molluscs were living in aqueous environments with peak mercury levels higher than today’s most polluted rivers, some by a whopping factor of eight. If that mercury compounded up the food chain—and it most likely did—the dinosaurs would’ve been dealing with potentially lethal poisoning. (See Figures 1 and 2 for an illustration of the whole deadly process!)

Further, clumped isotope paleothermy of the mollusc specimens showed that this all took place against a backdrop of a 5 to 12°C increase in global temperatures. To give you a point of comparison, our current climate change crisis has seen an average temperature increase of about 1°C since the Industrial Revolution.

So here’s the million-dollar question: Did the dinosaurs get merked by a meteorite, or did they die of concentrated mercury and a climate disaster precipitated by insane volcanism? Maybe the answer’s actually both, and the dinosaurs were just extremely unlucky.