In the early hours of August 16, Beijing time, the prestigious international academic journal Science published a groundbreaking paper revealing the source and nature of the Chicxulub asteroid, suspected to be the "culprit" behind a major biological extinction event.
In the newly published paper, researchers assessed samples collected from the Cretaceous-Paleogene boundary (K-Pg) to identify the origin and composition of the asteroid that caused the mass extinction 66 million years ago, uncovering that it originated from a rare carbonaceous asteroid beyond Jupiter.
Additionally, their findings indicated that meteorites from five other asteroid impact events over the past 541 million years originated from silicate (S-type) asteroids formed in the inner solar system, all of which were non-carbonaceous meteorites.
These discoveries contribute to resolving the long-standing debate regarding the nature of the Chicxulub asteroid, reshaping our understanding of Earth's history and the extraterrestrial rocks that collided with it.
Dr. Mario Fischer-Gödde, the corresponding author of the paper from the University of Cologne in Germany, stated, "Our future work will focus on investigating the ruthenium isotope characteristics from earlier asteroid impact events, which may have caused extinction events prior to the K-Pg boundary."
Mass Extinction Events
Throughout history, Earth has experienced several significant mass extinction events.
The most recent occurred 66 million years ago at the K-Pg boundary, resulting in the loss of about 60% of species on Earth, including non-avian dinosaurs.
The Chicxulub asteroid, a massive asteroid that struck Earth in what is now the Gulf of Mexico, is believed to have played a crucial role in this extinction event.
Was the Chicxulub impactor the sole cause of the extinction, or did simultaneous eruptions of the Deccan Traps contribute as well? This remains a contentious question.
In an interview with The Paper, Mario Fischer-Gödde expressed, "Personally, I believe that when a massive extinction occurs, the impact of a giant asteroid colliding with Earth is likely not coincidental."
Clay layers from the K-Pg boundary contain elevated concentrations of platinum group elements (PGE). These elements are quite rare in crustal rocks but are more abundant in certain types of asteroids.
Previous studies indicated that PGE data pointed to the Chicxulub asteroid being an asteroid with a composition similar to chondrites. However, little is known about the characteristics of the Chicxulub meteorite—its composition and extraterrestrial origin.
Platinum Group Elements in Identifying Extraterrestrial Meteorites
Mario Fischer-Gödde and his colleagues used the isotopic composition of ruthenium (Ru)—a platinum group element—to investigate the nature of extraterrestrial impactors. In addition to analyzing samples from the K-Pg boundary, they also examined samples from five other asteroid impacts over the past 541 million years, as well as samples from the Paleoproterozoic era (350 to 320 million years ago) associated with impact chondrites, and samples from two carbonaceous meteorites.
Ruthenium was chosen because it exhibits differences among various meteorite types, with ruthenium isotopic compositions that are also distinct from those of Earth. Thus, ruthenium can be used to determine the origin of the extraterrestrial components in impact rocks.
The ruthenium isotopic characteristics of meteorites vary according to the heliocentric distance of their parent asteroids during the early formation of the solar system (the distance from the Sun). Based on differences in isotopic composition across various elements, meteorites can be classified into two broad categories: carbonaceous chondrites (CC) and non-carbonaceous (NC) meteorites. In contrast, carbonaceous chondrites come from carbonaceous (C-type) asteroids that formed at greater heliocentric distances, beyond the orbit of Jupiter. Many non-carbonaceous meteorites are fragments of silicate (S-type) asteroids formed in the inner solar system.
Mario Fischer-Gödde and his team found that the Chicxulub meteorite, which caused the K-Pg boundary event, as well as ancient Paleoproterozoic chondrite samples, had ruthenium isotopic compositions distinct from that of Earth and overlapping with those of carbonaceous chondrites. This indicates that the Chicxulub meteorite originated from a body with carbonaceous chondrite-like components, suggesting its origin in the outer solar system. For the Paleoproterozoic chondrite, the carbonaceous chondrite components may have come from carbonaceous asteroid material that impacted the Earth during the late-stage accumulation of planets.
This evidence rules out the possibility that the elevated PGE levels found in the K-Pg boundary clay were a result of volcanic eruptions from the Deccan Traps, as well as the previous hypothesis suggesting a cometary origin for the Chicxulub meteorite.
