2026-07-28 パデュー大学
＜関連情報＞
- https://www.purdue.edu/newsroom/2026/Q3/dinosaur-killing-asteroid-also-created-a-dust-cloud-that-insulated-earth-charbroiling-cretaceous-creatures/
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2026JG009837
- https://www.nature.com/articles/nature10982
K-Pg大量絶滅期における熱と山火事は微細な塵によって増幅された Heat and Wildfires During the K-Pg Mass Extinction Enhanced by Fine Dust
Brandon C. Johnson, Alexandria V. Johnson, Shigeru Wakita, Douglas S. Robertson
Journal of Geophysical Research: Biogeosciences Published: 28 July 2026
DOI:https://doi.org/10.1029/2026JG009837
Abstract
The primary kill mechanisms responsible for the K-Pg mass extinction, including the end of the dinosaurs, are much debated. Here, we reexamine the hypothesis that heat and fire were the primary kill mechanisms for terrestrial organisms during the K-Pg mass extinction. We show that spherules and uncondensed vapor from the impact vapor plume are first ballistically transported globally and then decoupled spatially from one another when they encounter the atmosphere. Expanded K-Pg boundary sections provide strong evidence that this impact vapor ultimately condenses to abundant fine dust. The flux of thermal energy produced by impact spherules entering the atmosphere globally is strongly enhanced by the presence of this fine dust. This supports the idea that heat and fire were key kill mechanisms for terrestrial organisms.
衝突球は、地球への古代の激しい衝突の記録である Impact spherules as a record of an ancient heavy bombardment of Earth
B. C. Johnson & H. J. Melosh
Nature Published:25 April 2012
DOI:https://doi.org/10.1038/nature10982
Abstract
Impact craters are the most obvious indication of asteroid impacts, but craters on Earth are quickly obscured or destroyed by surface weathering and tectonic processes1. Earth’s impact history is inferred therefore either from estimates of the present-day impactor flux as determined by observations of near-Earth asteroids, or from the Moon’s incomplete impact chronology2,3,4. Asteroids hitting Earth typically vaporize a mass of target rock comparable to the projectile’s mass. As this vapour expands in a large plume or fireball, it cools and condenses into molten droplets called spherules5. For asteroids larger than about ten kilometres in diameter, these spherules are deposited in a global layer. Spherule layers preserved in the geologic record accordingly provide information about an impact even when the source crater cannot be found1. Here we report estimates of the sizes and impact velocities of the asteroids that created global spherule layers. The impact chronology from these spherule layers reveals that the impactor flux was significantly higher 3.5 billion years ago than it is now. This conclusion is consistent with a gradual decline of the impactor flux after the Late Heavy Bombardment.
