Scientists Uncover Origin of the Dinosaur-Killing Asteroid – Where Did It Come From?

On 15 August, an international team of scientists published the results of a multi-year study on the origin of the asteroid that collided with the Earth 66 million years ago. It wiped out three-quarters of all plant and animal species on Earth, most notably the dinosaurs. Also, it caused irreversible climate change that initiated the evolution of mammals, eventually leading to the emergence of humans.

‘Chicxulub’ object may come from out beyond Jupiter

The nature of this apocalyptic object, known as the Chicxulub Impactor and named after a community in present-day Mexico near a 90-mile-wide crater, has sparked much debate, including a long-running dispute over whether it was a comet or an asteroid. 

In recent years, however, there has been mounting evidence that the roughly six-mile-wide impactor belongs to a family of asteroids that form outside Jupiter’s orbit and rarely collide with Earth.

A team led by Mario Fischer-Goedde, a researcher at the University of Cologne in Germany, has strengthened the existing hypothesis with the rare element ruthenium.

The catastrophe created a global surface layer that marks the boundary between the Cretaceous and Palaeogene eras. This layer contains elevated platinum group elements such as iridium, ruthenium, osmium, rhodium, platinum and palladium. Because of the collision, these elements spread widely across the Earth.

Evidence from Ruthenium and Impact Layers

Ruthenium is abundant in asteroids but highly scarce in the Earth’s crust, making it a handy indicator of past collisions with space rocks.

It is so scarce on Earth that it only takes a small amount to link to a carbon-type asteroid impact. ‘That’s the beauty of the element ruthenium,’ Dr Fischer-Goedde said.

The scientists measured ruthenium isotopes in samples from three Cretaceous-Paleogene (K-Pg) sites from the Chicxulub impact crater, five other impacts that occurred between 36 million and 470 million years ago, and ancient impact layers between 3.5 and 3.2 billion years old.

The results showed a uniform signature on the global layer left by the impact, which matches the composition of a group of space rocks known as carbonaceous asteroids because of their high carbon content.

Five other impact structures have isotopic signatures that are more consistent with those of siliceous asteroids, which form closer to the Sun.

Siliceous asteroids that collide with Earth usually come from the asteroid belt. However, how a massive carbonaceous asteroid ended up on a collision course with our planet still needs to be determined.

One possible source is the population of carbonaceous asteroids that exist today on the outer edge of the asteroid belt. Although these rocks originally formed outside Jupiter, scientists believe that gravitational instability in the early solar system led to their current position.

David Kring, chief scientist at the University Space Research Association’s Lunar and Planetary Institute and an expert on the Chicxulub impact, said that ‘the study is an outstanding application of a new analytical method.’

‘Identifying the type of impact object is important because it helps us estimate the frequency of such impacts in the geological past and the risk of such impacts in the planet’s future,’ Dr Kring said.

Implications for Earth’s History and Future

Many mysteries remain about the Chicxulub impact and the broader role that asteroid impacts have played in the origin and evolution of life on Earth and possibly other planets. Carbonaceous asteroids have wiped out countless species in our planet’s past, but they may also have helped seed Earth with water and other ingredients necessary for life at the dawn of the solar system.

‘If not for this impact, what would our Earth look like today?’ – Dr Fischer-Goedde said. ‘We should probably appreciate a little bit more that we’re around, and maybe it’s a coincidence that everything fell into place the way it does today.’

Can the story of the dinosaur-killing asteroid now be considered complete?  

There is no unequivocal answer to that question. According to Kring, more sophisticated methods and tools should continue to explore the nuanced nature of space rock in the future. ‘Science rarely stops there,’ he said.