Scientists Finally Know Where the Dinosaur-Killing Asteroid Came From — At Least They Think

You’re reading this because something catastrophic terminated the more than 150-million-year reign of the dinosaurs.

What opened the doors for mammals to dominate Earth was likely an extraterrestrial object; probably an asteroid. Where that asteroid came from has not been entirely clear. But new research might have gotten a giant step closer to solving this mystery. According to a study published Thursday in the journal Science, the rogue space rock probably came from far beyond Jupiter, and was likely laced with traces from the stars that existed before the Sun.

The rocky body that felled Tyrannosaurus Rex and all our other favorite dinosaurs vaporized its 15-kilometer-wide self upon smacking into the Gulf of Mexico 66 million years ago. The force caused global tsunamis, earthquakes, and wildfires. A plume also shrouded Earth and peppered the planet’s surface with dust. This material has stood the test of time. It not only outlasted the eroded impact crater, but it packs chemical footprints that were forged inside stars older than the Solar System.

The cloud from which today’s planets grew contained an isotope of the element ruthenium (an isotope is distinctive type or variety of one element), which collected inside asteroids born in the Solar System’s outer edges. This isotope also appears in the Cretaceous-Paleogene (K-Pg) boundary, a thin layer of impact residue sandwiched between the rocks of the dinosaur-fossil-rich Cretaceous and those from the Danian period that followed, when biodiversity was in recovery.

In the K-Pg boundary, a signature for a ruthenium isotope looked uniform and matched two particular types of primitive meteorites known as carbonaceous chondrites. These are unlike the signatures from most of the asteroids that strike Earth, which come from the asteroid belt between Mars and Jupiter.

The finding suggests the dinosaur extinction came from an impact from an object that lived beyond the orbit of Jupiter. Perhaps by chance, or perhaps, by the force of the larger planets, it found itself on a collision course with Earth.

Our star and neighboring planets were created roughly at the same time. Their raw ingredients came from the life and death of the older generations of stars that lived in our corner of the cosmos a long time ago. This dust and gas made a molecular cloud. But the stuff wasn’t mixed well. Some regions had certain elements that were rarer in other pockets.

Ruthenium is a platinum-group element. It’s rare on Earth’s surface. But it’s found more commonly in asteroids, particularly those that came together farther away from the Sun during the early Solar System.

Ruthenium dwelled inside the dino-killing asteroid in the cold reaches of space. But when the rock struck Earth, creating what we call the Chicxulub crater, named for a town near the crater in the Yucatán Peninsula, the ruthenium survived. Mario Fischer-Gödde, planetary scientist at the University of Cologne, and his team found it in the K-Pg boundary in Spain, Denmark, and Italy.

“The terrestrial environments wouldn’t change this isotope signature. You can change some isotopic signatures on Earth, but not these nucleosynthetic ones,” Fischer-Gödde said. In other words, the ruthenium is robust because it was forged inside ancient stars. It stood up well to the force of the crash that created the Chicxulub crater. “They remain preserved even after a long time, even if they went through an asteroid impact,” he adds.

The asteroid was between 10 to 15 kilometers in diameter. “When a body like this is hitting the Earth with a velocity that’s estimated to be around 20 kilometers per second, this will release a lot of kinetic energy. You will immediately vaporize the asteroid itself, but also tons of terrestrial rock where the asteroid hit the Earth,” he said.

The dust settled worldwide, from Europe, to Asia, and even at the bottom of the ocean floor. “This can only happen if you have a massive asteroid impact.”

The dust plume blocked out the Sun, halting photosynthesis. The disruption to the food chain caused a die-out of 60 to 70 percent of all species on Earth, including all the non-avian dinosaurs.

It’s possible the dinosaur extinction was more complicated. Perhaps other factors, like volcanism in the Deccan Traps in India, are to blame. But the asteroid hypothesis is too large a coincidence to deny, Fischer-Gödde said. The dinosaurs were on the top of the food chain. They dominated the planet.

“Only with their disappearance was there a chance for us having this Zoom call today.”