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Stegosauruses ruffle through ferns; a lone velociraptor hunts in the desert; brachiosauruses bite leaves from ginkgo trees; a triceratops family looks up to see a flaming ball of fire plummeting towards Earth. This is one of the most recognizable scenes from our knowledge of Earth’s history. The Chicxulub crater under the Yucatán Peninsula of Mexico, where the Chicxulub asteroid left its mark, tells the story of how the mass extinction of the dinosaurs paved the way for the reign of mammals and, consequently, humans. But this crater also contains fascinating evidence of this famous asteroid’s extraterrestrial origins.
Scientists have debated whether an icy comet or a rocky, metallic asteroid caused the Cretaceous-Paleogene extinction. A new research study led by Mario Fischer-Gödde from the University of Cologne supports the latter theory and provides solid evidence for a new perspective: the Chicxulub asteroid was formed much further out in space than previously thought.
Fischer-Gödde came to this conclusion after analyzing samples taken from the Chicxulub impact zone. In order to differentiate between Earth soil and traces of ancient meteorite material, the research team chose to measure the concentration of ruthenium, an element that tends to be more abundant in meteorites. Ruthenium has various isotopes whose concentrations vary depending on the meteorite type. When the team analyzed the set of isotopes present in the soil, they found that the data was most similar to the typical concentration of ruthenium isotopes in carbonaceous chondrite (CC) meteorites. Concentrated amounts of CC meteorites in the soil from the impact zone suggest that Chicxulub was a carbonaceous asteroid. These types of asteroids form at distances beyond the orbit of Jupiter.
Most of the meteorites on Earth are from siliceous asteroids, which are formed in the inner solar system. So as prevalent as Chicxulub is in textbooks about Earth’s history, it is a relatively rare phenomenon to happen to Earth. How did an asteroid from more than 440 million miles away make its journey to Earth? One guess is that gravity pulled some carbonaceous asteroids into our solar system, causing them to settle into the Main Asteroid Belt between Mars and Jupiter. However, there is no definite answer.
The analysis technique used by the Fischer-Gödde research team may be very useful for future studies about meteorite impacts on Earth. The team also took samples from five impact zones that were thirty-six to 470 million years old, as well as samples from sedimentary deposits called spherule layers that were 3.2 to 3.5 billion years old. The ruthenium concentrations showed that the younger impact sites had meteorites from siliceous asteroids. On the other hand, the ruthenium in the spherule layers aligned with carbonaceous asteroids. In the future, ruthenium isotopes could be used in experiments to investigate more impact sites and study meteor collision trends at various points in Earth’s history.
The fact that the rise of humanity was dependent on an asteroid that, from over 440 million miles away, came to Earth on an extraordinarily specific collision course, could be an inspiring or disturbing revelation. Nevertheless, one thing is for certain: the history of the Earth is still a mystery to us, and many answers are right at our fingertips.