The Frasnian-Famennian boundary (FFB) biotic crisis is one of the ‘Big Five’ mass extinctions that took place during the Phanerozoic eon on Earth, and occurred roughly 375 to 360 million years ago. A team of scientists studying uranium-isotope profiles of a marine carbonate section have uncovered new details about the potential cause of this major event in life’s history. Previously, theories suggested that ocean anoxia may have been to blame for the extinction, however the new findings indicate that climatic cooling could have played a role.

The study, “Uranium and carbon isotopes document global-ocean redox-productivity relationships linked to cooling during the Frasnian-Famennian mass extinction,” was published in the journal Geology. The work was supported by NASA Astrobiology through the Exobiology & Evolutionary Biology Program.