Dinosaur-Killing Asteroid Had a Distant Origin

The asteroid that doomed the dinosaurs came to Earth from a distant neighborhood, researchers say. In a study published in the journal Science, researchers say analysis of isotopes confirmed that the asteroid that hit a site called Chicxulub 66 million years ago was a carbon-rich asteroid that formed in the outer solar system, beyond Jupiter. Carbonaceous, or C-type, asteroids hit the Earth less often than stony, silica-rich S-type asteroids. Researchers detected signs of S-type asteroids in five other major impacts from the last 500 million years. They say the finding rules out theories that the asteroid was really a comet.

• A rare metal. Mario Fischer-Gödde, an isotope geochemist at the University of Cologne, and his team measured isotopes of ruthenium, a metal that is very rare in the Earth's crust, Nature reports. They used the distribution of the isotopes to determine whether an asteroid formed in the inner or outer part of the solar system.

• A cosmic "fingerprint." Fischer-Gödde tells Scientific American that distribution of isotopes of ruthenium and other platinum-class metals is like "a fingerprint—these ratios are set by things like thermonuclear fusion inside stars that no process on Earth can replicate." With the Chicxulub impact, he says, the findings don't just show 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."
• A tedious process. Fischer-Gödde says the research involved the painstaking extraction of tiny specks of ruthenium from fist-sized pieces of rock to achieve a "ridiculously high precision of isotopic measurement." "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," he says.
• The asteroid's mysterious past. Fischer-Gödde says it's not clear where the asteroid was before it came to Earth. One possibility, he says, is the asteroid belt between Mars and Jupiter, where some C-type asteroids ended up after Jupiter migrated outward billions of years ago. "Maybe there was a collision of two asteroid bodies in the belt, and then this chunk kind of went on an Earth-crossing orbit," he tells the Guardian. Other possibilities, he says, include the Oort cloud beyond the solar system.

• We're here because of that asteroid. The cataclysmic impact ended up wiping out around 60% of life on Earth, including all non-avian dinosaurs. But since it led to the rise of mammals, "we may owe that rogue asteroid a measure of gratitude," the New York Times notes. "Without this impact, what would our Earth look like today?" Fischer-Gödde says. "We should probably value, a bit more, that we are around and this is maybe a lucky coincidence that everything came to place like it is today."

(More Chicxulub stories.)