Fine silicate dust from Chicxulub crater excavation shuts down photosynthesis for up to 2 years after the K-Pg impact. 

Formation of the ± 200 km in size Chicxulub crater is widely regarded as the leading cause of the Cretaceous-Paleogene (K-Pg) boundary mass extinction, 66 million years ago. Nevertheless, the precise climatic outcome of the various debris ejected into the atmosphere following the crater excavation, thus the killing mechanisms remain not definitely understood. Present paleoclimate scenarios confer a substantial role in sulfur components released by the vaporization of evaporite layers present in the upper part of the target rock. Sedimentological constraints acquired from an expanded terrestrial K-Pg boundary deposit in North Dakota and measured volumetric size distribution of silicate dust indicate the release into the atmosphere of fine silicate dust (~0.8-8 μm). The new general circulation model simulations of the injection of such a plume of micrometer-sized silicate dust (2x1018g) suggest a long atmospheric residence time (±15 years) with a global-average surface temperature falling by as much as 15ºC. Simulated effects on the post-impact active solar radiation support a dust-induced photosynthetic shut-down for approximately 2 years. Contrary to previous work, these new paleoclimate simulations, relying on robust sedimentological field data at the K-Pg boundary revealed that the impact-generated silicate dust plume plays a pivotal role in driving the K-Pg climate and biotic crisis. The new scenarios showcase that the global darkness and prolonged loss in the planet's photosynthetic activity happen solely in the silicate dust scenario, up to nearly 1.7 years after impact; a sufficiently long timescale to pose severe challenges for terrestrial and marine habitats. Biotic groups not adapted to survive the dark, cold, and food-deprived conditions for almost two years, experienced massive extinctions. In addition, this emission scenario shows that the photosynthetic recovery to the pre-impact levels first occurred in the austral summer season, ~1.7 years after impact. This would imply a potential earlier recovery of primary productivity in the Southern Hemisphere. These new findings highlight that the photosynthetic shut-down induced by the large volume of silicate dust, together with additional effects of sulfur and soot likely led to the collapse of primary productivity in land and ocean realms, steering the global mass extinction at the K-Pg boundary.