Fingerprinting the asteroid that determined the fate of the dinosaurs
A team of geoscientists, including members from the Archaeology, Environmental Changes and Geo-Chemistry large research unit of the Vrije Universiteit Brussel, has investigated traces of the asteroid impact that caused the extinction of the dinosaurs 66 million years ago.
The team examined samples from the Cretaceous-Paleogene boundary layer, which marks the extinction of 70% of all species that existed at the time, including the dinosaurs. According to the widely accepted theory, the mass extinction at the end of the Cretaceous was caused by the impact of an asteroid over 10 km in diameter on Earth, at the location of what is now the city of Chicxulub (Mexico). The asteroid itself and enormous amounts of target rocks from Earth were completely pulverized and vaporized due to the kinetic energy released during the impact. Fine dust particles spread around the globe and into the stratosphere, causing a reduction in sunlight and a halt to photosynthesis for several years, leading to dramatic changes in Earth's habitability. For years, the source and origin of the projectile within the solar system have remained a hotly debated topic in the scientific community.
The dust particles produced by the impact were deposited all around the globe in a clay layer representing the K-Pg boundary. The K-Pg boundary layer is exposed at many locations on Earth, and is well-known for its elevated concentrations of platinum-group elements (osmium, iridium, ruthenium, platinum, rhodium, palladium). The enrichment in the clay derives from the vaporized asteroid, as these elements are typically extremely rare in Earth’s crustal rocks.
By investigating the isotope composition of the platinum metal ruthenium in samples from the K-Pg boundary layer, the researcher team shows that the Chicxulub asteroid impactor originally formed in the outer solar system. “We found that the composition of the asteroid that impacted at Chicxulub is the same as that of carbonaceous meteorites, which are fragments of carbonaceous (C-type) asteroids that originally formed beyond the orbit of Jupiter” says Steven Goderis, one of the authors of the study.
For comparison, the team also analyzed the ruthenium isotope compositions of other terrestrial craters and ejecta layers of various ages in the geological record. These data show that within the last 500 million years the dominant compositions of bodies impacting on Earth were fragments of stony (S-type) asteroids. In contrast to the C-type asteroid impact at the K-Pg boundary, such S-type asteroids formed within the inner solar system. Indeed, about 80% of all meteorites hitting the Earth derive from S-type asteroids. Philippe Claeys, another of the coauthors of the study adds “Our results show that the impact of a C-type asteroid such as the Chicxulub impactor appears to be a rare and so far unique event in geological history, with a projectile originating at the very outskirt of the Solar System and sealing the fate of the dinosaurs.”
The study was published on 15 August 2024 in the scientific journal Science.
Contacte :
Prof Dr Steven Goderis Steven.Goderis@vub.be
Prof Dr Philippe Claeys phclaeys@vub.be
Tel non disponible auprès de la rédaction
AMGC, Université libre de Bruxelles
https://amgc.research.vub.be/
