26/08/2024
Cnr-Ismar researchers were part of the team led by the University of Cologne which has investigated traces of the asteroid impact that caused the extinction of the dinosaurs 66 million years ago: amongst the research team, there were researchers were part of the international panel of scientists.
The team analyzed samples from the Cretaceous-Paleogene boundary layer using a newly developed analytical technique focusing on the isotopic ratio of the very rare element ruthenium. The geologic boundary layer marks the latest major mass extinction event on Earth during which more than 70% of all species went extinct.
According to a widely accepted theory, the end-Cretaceous mass extinction was caused by the impact on Earth of a >10 km-diameter asteroid at Chicxulub (Mexico). The asteroid itself and huge amounts of terrestrial target rock were pulverized and vaporized owing to the kinetic energy released by the impact. Fine dust particles were distributed all around the globe and in the stratosphere where the dust caused a reduction of sunlight and photosynthetic shut-down for several years. This has to dramatic changes for the Earth’s habitability. For years, the source and origin within the Solar System of the projectile has remained a much-debated question.
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 Mario Fischer-Gödde, lead author 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. Carsten Münker, one of the coauthors of the study adds “Our results show that the impact of a C-type asteroid such as the Chicxulub impactor is a rare and until now unique identified event in more recent geologic history, with a projectile originating at the very outskirt of the Solar System and sealing the fate of the dinosaurs”.
The study is published in the scientific journal Science. Alessandro Bragagni, a researcher at Cnr-Ismar co-author of the study, added: “Our results show that Chicxulub is so far the only large C-type asteroid to have been identified in recent geological history.To find similar asteroids, we probably need to go much further back in geological time.Traces of such events are found in rock cores dating back billions of years”.
Per informazioni:
Alessandro Bragagni
Cnr-Ismar
alessandro.bragagni@cnr.it
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