End of the Big Beasts
The base of this "black mat," or layer of dark soil, marks the moment roughly 12,900 years ago when the hypothesized comet explosion occurred, wiping out most of North America's largest creatures in the ensuing natural disaster. Here, archeologist Vance Haynes, who first discovered the mat in this Arizona riverbed in the 1960s, points it out to geophysicist Allen West.