66 million years ago, the sudden extinction of the dinosaurs started the ascent of the mammals, ultimately resulting in humankind’s reign on Earth. Climate scientists have now reconstructed how tiny droplets of sulfuric acid formed high up in the air after the well-known impact of a large asteroid, which blocked the sunlight for several years, and had a profound influence on life. Plants died, and death cascaded through the food web. Previous theories focused on the shorter-lived dust ejected by the impact. New computer simulations show that the droplets resulted in long-lasting cooling, a likely contributor to the death of land-living dinosaurs. An additional kill mechanism might have been a vigorous mixing of the oceans caused by the surface cooling, severely disturbing marine ecosystems.