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**66 Million Years Ago: The Catastrophic Asteroid That Changed the Course of Life on Earth**
Sixty-six million years ago, a major turning point in the history of life on Earth occurred when an asteroid, measuring between 10 and 15 kilometers in diameter, struck the Yucatán Peninsula in Mexico. This catastrophe wiped out about three-quarters of Earth’s living species and marked the definitive end of the age of dinosaurs. The impact turned the asteroid into dust, which spread across the globe and is still present in a clay layer around the world that was deposited in the aftermath of that fateful day.
A new analysis of this debris has finally settled a long-standing debate about the nature of the asteroid, revealing that this celestial body originated from a region beyond Jupiter in the outer solar system. Based on the composition of the debris, the object that struck Earth was a carbonaceous asteroid, referred to as a type (C) asteroid, named for its high carbon content. The study ruled out the possibility that the impactor was a comet or that the debris layer resulted from volcanic activity, as some had previously suggested.
### An Impact That Sealed the Fate of the Dinosaurs
Geochemist Mario Fischer-Gödde from the University of Cologne in Germany, the lead author of the study published on Thursday in the journal Science, stated, “An impactor launched from the outer reaches of the solar system sealed the fate of the dinosaurs.” The collision at the end of the Cretaceous period created the Chicxulub crater, which measures 180 kilometers in diameter and 20 kilometers in depth. The clay layer is rich in iridium, ruthenium, osmium, rhodium, platinum, and palladium—metals that are rare on Earth but common in asteroids.
The researchers focused on ruthenium, specifically the ratio of its isotopes present in the clay layer. Isotopes are atoms of the same element with slightly different masses due to varying numbers of neutrons. Ruthenium has seven isotopes, three of which were particularly significant in the study’s findings. The isotope ratios of ruthenium in the clay layer matched those found in other known carbonaceous asteroids.
### Isotope Ratios
Geologist Steven Goderis, a co-author of the study from Vrije Universiteit Brussel in Belgium, explained, “Ruthenium is especially useful in this context because the isotope ratios in the clay layer consist almost entirely of the ruthenium from the impactor… The ruthenium shows distinct isotope compositions present in materials from both the inner and outer solar system.”
Type C asteroids, among the oldest bodies in the solar system, are the most common type of asteroids, followed by the stony type (S) asteroids and the rare metallic type (M) asteroids. The differences in composition among asteroids arise from their varying distances from the Sun when they formed.
Fischer-Gödde noted, “Type C asteroids represent the remaining building blocks of the gas and ice giants in the outer solar system, whereas type S asteroids are the building blocks of terrestrial planets like Earth in the inner solar system.” He added that after forming in the outer solar system, the asteroid likely migrated inward to become part of the main asteroid belt between Mars and Jupiter, before being sent toward Earth, possibly due to a collision.
He continued, “All meteorites that have fallen to Earth are fragments of type C and S asteroids that originated in the asteroid belt. Therefore, it seems likely that the object that struck Earth at the end of the Cretaceous period also originated from the asteroid belt… But there are also many bodies stored in the Kuiper Belt and the Oort Cloud (regions far beyond the outermost planet, Neptune), and little is known about the composition of these bodies.”
The researchers analyzed debris samples from five other asteroids that collided with Earth between 37 million and 470 million years ago, and found that they were all of the S-type, highlighting the rarity of impacts involving carbonaceous asteroids.
### The Aftermath of the Impact
Dinosaurs dominated Earth for a long time, but except for the avian lineage, they became extinct after this impact. Flying reptiles known as pterosaurs, large marine reptiles, and other marine creatures, including certain types of plankton, also vanished. Mammals, however, managed to survive, allowing these furry creatures to eventually dominate Earth, paving the way for the emergence of the human species around 300,000 years ago.
Fischer-Gödde remarked, “I believe that without this cosmic coincidence of the asteroid impact, life on our planet might have evolved very differently.”
—by/radwa sherif ✏️✏️📚