"Mercury Rising" --Is to Earth-Based Mass Extinction What Iridium is to Extraterrestrial Ones"

In other mass extinctions, elevated mercury has been closely linked to big-time volcanic episodes. In fact, points out geologist Grzegorz Racki, mercury has become to Earth-based catastrophes what iridium is to extraterrestrial-based ones. "Mercury as a geochemical fingerprint of volcanism...