A cataclysmic shift at the end of the Ordovician led to the disappearance of about 85% of species at a time when life was mostly limited to the seas.“Their link to those mass extinctions ...

Researchers first identified the cause of the end-Cretaceous extinction by the discovery of the “iridium anomaly” — a 1-centimeter-thick (0.4-inch-thick) layer of sedimentary rock rich in ...