Reevaluating Links Between Meteorite Impacts and Early Cenozoic Global Warming

The Paleocene‐Eocene Thermal Maximum (PETM) and the lower Chron 29n hyperthermal event were recently proposed to have been triggered by the meteorite impacts that formed the Marquez Dome (Texas, USA; 58.3 ± 3.1 Ma) and Boltysh (Ukraine; 65.39 ± 0.14 Ma) craters, respectively. We use shock physics hydrocode simulations and radiative forcing calculations to quantify the expected global temperature increase associated with impacts of different scales via the release of CO2 and CH4 sourced from target rocks into the atmosphere. Our results suggest that the 1 K) temperature changes, even if target rocks were carbon‐rich; >10 km diameter impactors may produce hyperthermal events, but such large impacts are predicted to be uncommon during the Cenozoic era (2–4 objects per Gyr). Plain Language Summary Global warming events occur when temperature on Earth rises by a few degrees in a geologically short time period. Such events occurred approximately 25 times between 66 and 52 million years ago, but their causes are poorly understood. The meteorite impacts that formed the Marquez Dome (Texas, USA) and the Boltysh (Ukraine) craters have both been hypothesized to have triggered global warming events by releasing greenhouse gases. We found that the impacts which produced those craters are too small to be the sole cause for a significant temperature increase. Instead, impactors greater than 10 km in diameter are needed for substantial global warming to occur. Such large impacts would rarely occur within the past 100 million years, but were much more frequent early in Earth history. Key Points Objects larger than 10 km are required to vaporize greenhouse gases capable of inducing multidegree global warming The impacts that produced the Boltysh and Marquez Dome craters were too small to trigger early Cenozoic hyperthermal events