Unveiling the True Origins of the Dinosaur-Killing Asteroid

[Social Media]

 

Sixty-six million years ago, Earth experienced one of the most catastrophic events in its history. A mountain-sized asteroid hurtled from the sky at unimaginable speed, crashing into what is now the Yucatán Peninsula in Mexico. The impact was so powerful that it released energy equivalent to 100 million nuclear bombs, creating a 200-kilometer-wide crater, triggering massive earthquakes, tsunamis, and firestorms, and casting a shroud of dust and vaporized rock across the planet. This cataclysmic event led to the extinction of more than half of all species on Earth, including the dinosaurs, and set the stage for the rise of mammals, including our own ancestors.

 

 

For decades, scientists have sought to unravel the mystery of this extinction event. It was in the 1970s and 1980s that physicist Walter Alvarez and his colleagues began to piece together the puzzle. They discovered a layer of debris in rocks dating back 66 million years that was rich in iridium, an element rare on Earth but abundant in asteroids and comets. This discovery led them to link the extinction event to a massive impact, and they identified the now-submerged Chicxulub crater as the site of the impact. However, questions remained: Was the impactor an asteroid or a comet? What kind of space rock was it, and where did it come from? Could the iridium and the mass extinction have been caused by volcanic activity rather than an extraterrestrial impact?

 

 

A recent study published in *Science* on August 15 provides the most definitive answers yet to these questions. Through precise measurements of ruthenium isotopes found in the debris of the impact, the study conclusively shows that the material did not come from volcanism but from an extraterrestrial source. The variations in the isotopes suggest that the Chicxulub impactor was not a comet or an ordinary asteroid but a carbonaceous asteroid, rich in carbon and organic compounds.

 

"I find these results very convincing," says Steve Desch, an astrophysicist at Arizona State University who was not involved in the study. "They dovetail nicely with lots of other evidence." This evidence includes earlier measurements of other isotopes and minerals in the debris layer, as well as geochemical studies of fragments of the impactor that scientists have recovered from ancient sediments. Desch and others believe that the available evidence strongly points to the impactor being a carbonaceous asteroid, although absolute certainty would require more detailed studies of cometary material, which researchers have not yet obtained.

 

The new study's interpretation is not entirely new. Richard J. Walker, a geochemist at the University of Maryland, points out that a similar conclusion was reached in a 1998 study that analyzed a chromium isotope. However, he notes that the recent study presents a much more robust determination that the Chicxulub impactor was indeed a carbonaceous asteroid.

Carbonaceous asteroids are relatively rare and are thought to have formed in the outer solar system beyond Jupiter before Earth itself coalesced.

 

These asteroids were later sent into the inner solar system's asteroid belt by the gravitational interactions of the giant planets more than 4.5 billion years ago, shortly after the sun began to shine. Some scientists suggest that this influx of organic material from the outer solar system may have provided the early Earth with the essential chemical building blocks of life, as well as much of the water that now fills its oceans. In a grand, almost poetic sense, the same process that helped kick-start life on Earth also set the stage for the extinction of the dinosaurs and the emergence of mammals.

 

"This impact totally changed the picture of our planet and caused the emergence of mammalian life," says Mario Fischer-Gödde, a geochemist at the University of Cologne in Germany and the lead author of the new study. "And it follows from a sequence of events that began in the very early days of the solar system so that, more than four billion years later, you and I are able to sit here having this conversation."

 

Ruthenium, the element central to this study, is a silvery metal that, like iridium, belongs to the "platinum group" of elements. These elements are rarely found on or near Earth's surface because they are siderophile, or iron-loving, elements. During Earth's formation, when the planet was still a partially molten mass, these elements sank into the planet's core along with iron. This means that almost all the platinum group elements in Earth's crust were delivered there later by meteorites, asteroids, and comets that struck the planet after it had cooled. This makes them excellent tracers of impact events throughout Earth's history.

 

For the Chicxulub event, Fischer-Gödde and his team have shown that the ruthenium found in the debris layer is almost entirely from the impactor itself. Ruthenium is particularly useful because it has more isotopes to examine than most other platinum-group elements. These isotopes are produced by different astrophysical processes, such as supernova explosions or the slow fusion processes in stars, and their ratios can help scientists trace the origins of the material.

 

About 15 years ago, scientists discovered that asteroids display a curious isotopic dichotomy: those that formed closer to the sun have one set of isotopic ratios, while the carbonaceous ones that formed farther out have another. This discovery allows researchers to use isotopic variations to determine whether an impactor was carbonaceous and, by extension, where it formed in the solar system.

 

"These stellar nucleosynthetic variations in isotopes help trace how different parts of the solar system evolved during its earliest formation," says James Day, a geochemist at the University of California, San Diego's Scripps Institution of Oceanography, who reviewed the study. "What's so exciting is that Mario and his team have used these ruthenium isotopes as a fingerprint to identify where the Chicxulub impactor came from."

 

The study involved analyzing seven ruthenium isotopes using a technique called multicollector inductively coupled plasma mass spectrometry. Fischer-Gödde and his colleagues sampled the ruthenium from the dinosaur extinction layer at three different sites around the world, as well as from carbonaceous meteorites and other craters from different impacts over the past half-billion years. They also examined ruthenium from ancient rocks dating back 3.5 billion years, which contain debris from a period of intense bombardment.

 

By measuring all seven ruthenium isotopes and checking their ratios against those expected from astrophysical processes, the researchers were able to rule out terrestrial effects and confirm the extraterrestrial origin of the material. "That's why this is like a fingerprint," Fischer-Gödde explains. "These ratios are set by things like thermonuclear fusion inside stars that no process on Earth can replicate. We measured, we checked, and it all lines up... So, for the Chicxulub event, our result isn't just showing it was a carbonaceous asteroid—it's also the nail in the coffin for the idea that these platinum-group elements came from volcanism or any other terrestrial origin."

 

The process of separating the ruthenium from the rocks was grueling and required extreme precision. Richard J. Walker describes the painstaking effort: "For many of these samples, we're talking about taking a fist-sized piece of material, 20 to 30 grams of rock, and extracting a little speck you probably can't see without a microscope. That's what you have to do to reach this ridiculously high precision of isotopic measurement."

 

Fischer-Gödde acknowledges the difficulty of the work, noting that he has spent the past decade perfecting his technique. "I'm German, and so I'm normally humble, but I'm comfortable saying I'm the world's leading expert in this—because it's so tedious, there are only a few people on the planet doing it."

 

The hard work has paid off. Of the impact events studied from the past half-billion years, only the Chicxulub event showed a distinct carbonaceous, outer-solar-system mix of ruthenium isotopes. The other impacts were caused by stony asteroids from closer to the sun. The ruthenium ratios from the most ancient impacts suggest that Earth was bombarded with carbonaceous material from the outer solar system during its early history. This bombardment is thought to have been caused by a dynamical instability that rearranged the orbits of the giant planets shortly after the solar system formed, sending waves of impactors toward the inner solar system.

 

Future studies could involve analyzing ruthenium and other isotopes from various sources, including comets and lunar craters, to further understand the impact events that have shaped Earth's history and to determine the exact type of carbonaceous asteroid responsible for the dinosaurs' extinction.

 

Two significant questions remain: how did the Chicxulub impactor make its way to Earth billions of years after it was ejected from the outer solar system, and when might the next similarly sized asteroid strike Earth? Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who was not part of this study, believes that he and his colleagues have already found the answers.

 

In a 2021 paper, they used dynamical modeling to suggest that the impactor came from the central to outer main asteroid belt. Bottke also estimates that Chicxulub-class objects strike Earth once every 250 million to 500 million years, suggesting that we have a low probability of facing another cataclysmic asteroid impact any time soon.

 

Credit: Scientific American  2024-08-19

 

 

Get our Daily Newsletter - Click HERE to subscribe

 

Cigna offers a variety of health insurance plans designed to meet the minimum requirement for medical treatment coverage, with benefits reaching up to THB 3 million. These plans are tailored to provide comprehensive healthcare solutions for expatriates, ensuring peace of mind and access to quality medical services. To explore the full range of Cigna's expat health insurance options and find a plan that suits your needs, click here for more information.