Scientists now believe they know where the asteroid that wiped out the dinosaurs came from

About 66 million years ago, something huge hit our planet off the coast of what is now the Yucatan Peninsula. The projectile was estimated to be 10 to 15 kilometers in diameter, it produced an explosion of 90 million megatons, a planetary shock wave, and a huge tsunami. And according to the leading theory, it was responsible for a mass extinction that wiped out the dinosaurs.

But there was always debate about what exactly it was: Was it a comet or an asteroid?

Well, a new study A study published in the journal Science found that it was indeed an asteroid – a so-called carbonaceous type – that came from outside Jupiter's orbit.

The authors of the study made the discovery by studying the isotope of ruthenium, a rare element that belongs to the platinum group elements (PGEs).

Ruthenium is one of the rarest elements on Earth, at just 0.001 ppm. However, it is believed that there is much more of it in the Earth's core. This is because when the Earth was formed 4.6 billion years ago, much of it was destroyed by a molten sea when rocks collided.

However, it is present in some asteroids, especially those beyond Jupiter, where it is preserved in a kind of cold storage.

Our solar system contains many remnants from the time of its formation. Comets are dusty and icy remnants, whereas asteroids consist mainly of rock. Meteorites or small pieces of rock fall to Earth every now and then. Scientists' knowledge of the composition of asteroids comes mainly from these remnants.

However, not all asteroids are made of the same material. There are three main composition classes of asteroids: C-types (carbonaceous); S-types (stony); and M-types (metallic).

Cosmic fingerprint

The asteroid that is believed to have wiped out the dinosaurs struck Earth 66 million years ago between the Cretaceous and Paleogene periods, known as the K-Pg boundary. While scientists cannot study the asteroid itself because it was destroyed, they can study the isotopes left behind – in this case, ruthenium.

“The isotope signatures we measure can be considered a kind of fingerprint,” said lead author Mario Fischer-Gödde, who is also a scientist at the Institute of Geology and Mineralogy at the University of Cologne. “So when there is a large impact, we vaporize rock and the asteroid itself, but this fingerprint remains.”

They also examined ruthenium isotopes in five other samples from the last 541 million years, as well as in samples from about 3.2 to 3.5 billion years ago and in another from two carbonaceous meteorites. They also took measurements at locations in Europe where debris from the event can be found, the so-called distal sites.

They found that ruthenium isotopes from the K-Pg boundary were very similar to those from carbonaceous meteorites.

“All the results clearly show that no matter which site we examine, they all consistently show the same isotopic signature of a C-type asteroid material,” said Fischer-Gödde. “That's why we can be quite confident about this.”

Although the study rules out a comet, Fischer-Gödde noted that no sample has yet been taken from the nucleus of a comet.

“I'm a scientist. I consider all possible outcomes, complexities and so on,” he said.

Paul Wiegert, a professor in the Department of Physics and Astronomy at Western University in London, Ontario, said he found the study, in which he was not involved, made a compelling argument.

“It’s a very interesting article,” said Wiegert.

He said the strong ruthenium signature is exactly what scientists expect to find in asteroids, so the discovery in the Earth's crust is good evidence.

“I would say it's pretty convincing,” he said. “Ruthenium is very rare in most objects in the solar system. In the Earth's crust, for example, it's pretty rare. … I think they've made the connection in a very convincing way.”

Fischer-Gödde also looks at this finding philosophically.

“A large C-type asteroid impact in recent Earth history, say in the last 500 million years … that's really a rare and unique occurrence, and this event: we can call it a cosmic coincidence, but without this event we probably wouldn't be sitting here,” he said.

“Our ancestors would probably never have dared to crawl out of their caves. They would have been eaten by the dinosaurs.”