"Mutant" Fossils Reveal Toxic Metals May Have Contributed to World's Largest Extinctions
|A malformed ('teratological') chitinozoan specimen of the genus Ancyrochitina (a) and a morphologically normal specimen (b) of the same genus. Both of these Silurian microfossils are from the A1-61 well in Libya and are about 415 Ma old. Scale bars are 0.1 mm. (High resolution image)|
Toxic metals such as iron, lead and arsenic may have helped cause mass extinctions in the world's oceans millions of years ago, according to recent research from the U.S. Geological Survey, the National Center for Scientific Research, France; and Ghent University, Belgium. These findings largely came from studying "teratological" or malformed fossil plankton assemblages corresponding to the initial stages of extinction events approximately 420 million years ago that killed off most marine species
At that time, several mass extinction events shaped the evolution of life on our planet. Some of these short-lived events were responsible for eradication of up to 85 percent of marine species, however the exact kill-mechanism responsible for these crises remains poorly understood.
In a paper just published in Nature Communications, the scientists present evidence that malformed fossil remains of 415 million- year-old marine plankton contain highly elevated concentrations of heavy metals of the kind that can cause morphological abnormalities in today's marine life. This led the authors to conclude that metal poisoning caused the observed malformation and may have contributed to the extinction of these and many other species.
"This paper is a testament to the power of multi-disciplinary research," said USGS scientist Poul Emsbo, a lead author of the report. "Here, collaboration between a paleontologist and an ore-deposit geochemist has led to new data that unveils new processes that may ultimately explain the cause of catastrophic extinctions in earth history."
The documented chemical behavior of the toxic metals correlates with previously observed disturbances in oceanic carbon, oxygen and sulfur signatures. Such behavior strongly suggests that these metal increases were a result of decreased oxygen in the ocean.
Thus, metal toxicity, and its expressions in fossilized malformations, could provide the missing link that relates organism extinctions to a widespread absence of ocean oxygen. As part of a series of complex systemic interactions accompanying oceanic geochemical variation, the mobilizations of metals in spreading low-oxygen waters may identify the early phase of the kill-mechanism that led to these catastrophic extinction events.
The recurring correlation between fossil malformations and Ordovician-Silurian extinction events raises the provocative prospect that toxic metal contamination may be a previously unrecognized contributing agent to many, if not all, extinction events in the ancient oceans.