Abstract: Sixty-six million years ago a 6-mile-wide asteroid slammed into Earth and caused the extinction of more than 75% of life on Earth, including the dinosaurs. This was the single worst day for life on Earth. How and when life rebounded in the aftermath of the extinction has been shrouded in mystery due to a poor fossil record. An extraordinary new discovery in the Denver Basin in Colorado preserves a remarkably complete fossil record with entire fossil mammals, turtles, crocodiles, and plants and paints a vivid picture of how life rebounded after Earth’s darkest hour.