The dominant model of Earth’s deep past has long been gradualism — the idea that change happens slowly, over millions of years, through steady incremental processes. But a growing body of evidence points to something far more dramatic: periodic catastrophic events that reshaped landscapes, drove mass extinctions, and may have wiped out human civilizations that left only myths behind.
The Younger Dryas period (roughly 12,900–11,700 years ago) is the most intensely studied of these proposed catastrophes. Something — whether a comet impact, a solar event, or a cascading series of ice-dam failures — caused global temperatures to plunge, megafauna to vanish, and at least some human populations to collapse. The Younger Dryas Impact Hypothesis, first proposed in 2007 and supported by a growing number of peer-reviewed studies, argues for an extraterrestrial trigger. The debate is fierce and ongoing.
Flood geology — the study of large-scale flood events and their geological signatures — offers another lens. The catastrophic draining of glacial Lake Missoula, for example, carved the entire Channeled Scablands of Washington State in what geologists now accept was a matter of days, not millennia. If that scale of change is possible, what else might have happened quickly that we’ve attributed to slow processes?