The asteroid responsible for the extinction of the dinosaurs was a rare celestial body of an atypical class

A Cosmic Impact: Its Origins Finally Revealed

The metal left behind by the meteorite that formed the Chicxulub impact crater and caused the extinction of most living species on Earth has a very distinctive isotopic signature. For decades, the exact origin of this celestial body has been the subject of heated debate within the scientific community. While the media generally refer to this impactor as an asteroid, several astronomers have long argued that it was more likely a comet from the Kuiper Belt or even more distant regions.

New research led in part by Dr. Philippe Claeys of the University of British Columbia has succeeded in providing precise answers regarding the nature of the projectile. As reported in a study published as open access in the journal Science Advances, analysis of nickel deposited in a geological layer around the globe points to an asteroid belonging to the carbonaceous chondrite class, thereby calling into question certain established scenarios regarding the course of this mass extinction.

Meteorites that have reached Earth can be categorized based on the abundance of their chemical elements or basic molecules, such as water. These characteristics include traces of metals left in the soil. Thanks to these molecular signatures, researchers were able to refine the classification of the celestial body that wiped out the non-avian dinosaurs at the end of the Cretaceous period.

The isotopic signature of the Cretaceous–Paleogene boundary

The main clue that initially led geologists to suspect that an extraterrestrial object had brought the Cretaceous to an end lies in a rock layer that is extremely rich in metals. Known as the KPg boundary, this stratum marks the exact moment when the Cretaceous ended and the Paleogene began. It contains metals that are extremely rare in the Earth’s crust, composed of a mixture of isotopes whose proportions are particularly revealing.

Analyzing these residues poses a real technical challenge for researchers. “It’s difficult work,” said Dr. Philippe Claeys in a press release. “Only a tiny fraction of the projectile is preserved in the planet’s [KPg] clay layer because the entire meteorite vaporized upon impact.”

To overcome this obstacle, the scientific team studied the ratios of the five stable nickel isotopes extracted from KPg layer samples collected around the world. These high-precision analyses made it possible to isolate the specific isotopic signature of the impactor despite its near-total vaporization during the instantaneous collision.

Identification of an atypical meteorite from the Ornans class

Previous studies had suggested that the fireball was likely a carbonaceous chondrite, a category of space rock that accounts for only 5% of recorded meteorites and is characterized, as its name implies, by its high carbon content. However, the study led by Claeys and his co-authors revealed an additional detail: the isotopic composition of the nickel matches that of an even rarer subgroup called the Ornans class (or CO group).

This category of asteroids is distinctly different from the conventional extraterrestrial rocks found on our planet. These distant celestial bodies exhibit an atypical chemical signature that alters researchers’ understanding of the meteor’s raw composition.

As Dr. Philippe Claeys explains: “Carbonaceous chondrites of the Ornans class are definitely unlike the typical meteorites found in museum collections. A CO contains far fewer volatile elements—such as carbon, zinc, water, and especially sulfur—than the other classes of meteorites we have discovered so far on Earth.”

Rethinking the Role of Sulfur in the Cataclysm

Historically, models simulating the global climate after the impact attributed a major role to the sulfur delivered by the meteorite. Scientists believed that this element had largely contributed to the formation of airborne particles capable of blocking sunlight for several years, leading to global cooling and the extinction of most life.

If the Chicxulub asteroid contained significantly less sulfur than predicted, the mechanisms behind this global cooling must be reevaluated. The sulfur supply derived directly from the impactor no longer appears to be the primary trigger for solar dimming.

Dr. Philippe Claeys clarifies this crucial distinction: “This does not change our theory about what caused the extinction event, but it makes it less likely that the sulfur contained in the impactor was the trigger. The fine debris ejected into the atmosphere would have been the primary factor.”

A Cosmic Tragedy for the Dinosaurs

These findings shed light on the unique chain of events that led to the end of the great reptiles’ reign. Although spared from a massive shower of toxic sulfur directly released by the asteroid, the living organisms of the time were unable to survive the cloud of dust and soot ejected at high altitude during the colossal impact.

The extreme rarity of this type of impactor underscores the sheer bad luck that befell the Cretaceous fauna. “Being struck by such a rare and distant impactor highlights just how unlucky the dinosaurs were,” noted Claeys regarding the findings published in Science Advances.

This isotopic analysis of nickel provides a crucial piece of the puzzle regarding the Late Cretaceous mass extinction event. It confirms that if the trajectory of this atypical asteroid had not crossed that of Earth, the evolution of life and the emergence of mammals might have taken a completely different course.

Source: iflscience.com

The asteroid responsible for the extinction of the dinosaurs was a rare celestial body of an atypical class