A 100 million megaton impact would be a catastrophic event, far exceeding any known impact in Earth's history. The Chicxulub impact, which is believed to have caused the extinction of the dinosaurs, was roughly 100 million megatons. An impact of this magnitude would cause widespread devastation, including earthquakes, tsunamis, wildfires, and a global dust cloud that would block out the sun, leading to a prolonged impact winter. While the Earth itself would survive, life as we know it would be drastically altered, and much of it would be extinguished.
