Although far smaller than the asteroid that killed the dinosaurs, the near-Earth asteroid Bennu could still cause substantial global damage if it strikes Earth in 2182 CE. Now, new modeling estimates the devastation that could result from the impact of a medium-sized asteroid such as Bennu, which has a 1-in-2700 chance of impact. According to the study's findings, dust, aerosol, debris, and ash injections into the atmosphere could cool Earth by 4 degrees Celsius and reduce rainfall by 15%, triggering a global winter and extreme drops in net primary productivity. "Asteroid impacts have taken place many times in Earth’s history. Our early human ancestors may have experienced some of these planet-shifting events before with potential impacts on human evolution and even our own genetic makeup,” co-corresponding author Lan Dai told the VancePak team in an email. “This study provides the basis to quantify the possible effects of abrupt events on early human evolution.” Should the Earth be remarkably unlucky, Bennu will strike the planet 157 years from now. However, the outcomes of this unlikely impact have been hard to predict. The last known large asteroid that hit Earth was the dinosaur-killing asteroid, which created the Chicxulub crater over 66 million years ago. While this behemoth was 10 kilometers across, Bennu is far smaller, with only a 500-meter diameter. As such, its devastation might be less extreme but could still upend the global ecosystem. Here, Dai and co-corresponding author Axel Timmermann predicted the possible outcomes of 4 stratospheric injection scenarios from a medium-sized asteroid strike. They combined an Earth system model (high-top Community Earth System Model Version 2) with an atmospheric chemistry model (Whole Atmosphere Community Climate Model Version 6). Under the worst-case scenario where up to 400 million tons of dust reach the atmosphere, ozone could fall by 32%, temperature could drop by 4 degrees Celsius, and precipitation could lessen by 15%. A resultant “impact winter” caused by lingering dust could then severely affect global photosynthesis: Terrestrial net primary productivity (NPP) could plummet by up to 36% and marine NPP by up to 25%. However, if the asteroid produced particularly iron-rich dust, diatoms could bloom in the eastern equatorial Pacific and Southern Ocean for three subsequent years. The authors note that these results do not account for further effects from soot and sulfur emissions by impact wildfires.