The ice age world supported at least twice as many large megafauna species as exist today. Within just a few thousand years, half of them vanished completely, leaving no viable populations to recover. No woolly mammoths walking through the Adirondacks, no mastodons in modern forests. The extinction was so thorough that entire lineages disappeared without a trace. What could cause such rapid, wholesale elimination of species that had survived for hundreds of thousands of years? The timeline matters here: this wasn't gradual attrition over epochs, it was a geologically instantaneous collapse of biodiversity across multiple continents.