Plummeting ocean reserves of selenium could have played a part in past mass extinctions.

Selenium and other trace elements help certain enzymes to function and perform other essential biochemical duties in organisms. John Long at Flinders University in Adelaide, Australia, and his team estimated ocean selenium levels over the past 560 million years by analysing it in marine pyrite samples. Selenium concentrations fluctuated drastically, but sharp drops coincided with several mass extinctions — including one at the end of the Triassic 200 million years ago.

Crashes in selenium levels may have acted in concert with changes in oxygen and carbon cycles to drive mass extinctions, the authors say.

Gondwana Res. http://doi.org/834 (2015)