They are eruptions so vast, so Earth-shattering, they have changed the history of our planet. Climate collapse. Toxic turmoil. Mass extinction. Worse than a killer asteroid, or nuclear war, they are Earth's most destructive Supervolcanoes. North America, the time was six hundred and forty thousand years ago, long before humans arrived on the continent. Amid one of nature's great mountain building projects, the Rockies, vast columns of smoke began to rise high into the atmosphere. And soon a smokey haze wrapped the globe.