New Study Pinpoints Outer Solar System Origins of Dinosaur-Dooming Asteroid

In a groundbreaking study published in Science, researchers have determined that the asteroid responsible for the mass extinction event that ended the age of dinosaurs originated from the outer solar system, beyond the orbit of Jupiter. The study, led by geochemist Mario Fischer-Gödde, in collaboration with geoscientist Steven Goderis, reveals that the composition of debris from the tragic event—which eradicated about three-quarters of the planet's species—matches that of a carbonaceous, or C-type, asteroid.

These revelations were made possible by analyzing the global clay layer formed from the asteroid's impact debris, specifically focusing on ruthenium isotope ratios. Isotopes are variants of a particular chemical element that differ in neutron number, and their ratios can point to the origin of materials. Ruthenium, with its distinct isotopic signature, is a clinching evidence in this investigation, overwhelmingly favoring the scenario where the impactor was a carbonaceous asteroid formed at the fringes of the solar system.

The study has dismissed the possibility that the debris layer could be attributed to a comet impact or volcanic activity, resolving a longstanding debate in the scientific community. The findings also highlight the compositional variations among asteroids, ranging from C-type asteroids, considered remnants from the formation of gas and ice giants, to S-type and M-type asteroids, which are typically associated with the inner solar system.

The researchers suggest that the asteroid initially formed in the outer reaches of the solar system and then migrated to the main asteroid belt between Mars and Jupiter. It is from this belt that it was likely set on a collision course with Earth, leading to the Cretaceous-Paleogene extinction event that formed the Chicxulub crater in Mexico's Yucatan Peninsula. The devastating impact led to the extinction of numerous species, including non-avian dinosaurs, pterosaurs, and many marine organisms.

This new insight emphasizes the rarity of such catastrophic impacts by carbonaceous asteroids, as the team also analyzed five other asteroid impacts from various periods, all of which were identified to be S-type. The contrast underlines the role of chance in Earth's history, suggesting that without this cataclysmic event, life on our planet might have evolved very differently, and our existence as a species would not have been guaranteed.

The aftermath of the asteroid impact was a new beginning for mammalian evolution, as these small, resilient creatures were afforded an opportunity to flourish and eventually gave rise to humans, who would emerge some 66 million years later.