The asteroid that destroyed the dinosaurs originated from beyond Jupiter

The impact of the Chicxulub asteroid hurled rocks into Earth’s atmosphere, burned the planet’s forests to ashes and triggered tsunamis that spread far and wide across oceans. | Photo Credit: NASA/Reuters

This was a turning point in the history of life on Earth. 66 million years ago, an asteroid estimated to be 10-15 km wide struck Mexico’s Yucatan Peninsula, triggering a global cataclysm that wiped out about three-quarters of the world’s species and ended the age of the dinosaurs.

The collision destroyed the asteroid and scattered its debris across the world, still present today in a global layer of soil deposited after that fateful day. A new analysis of this debris has settled a longstanding debate about the nature of the asteroid, showing that it was a type of asteroid that originated in the outer solar system, beyond Jupiter.

Based on the composition of the debris, the impactor was a carbonaceous asteroid, or C-type, so named because of the high concentration of carbon. The study ruled out that the impactor was a comet or that the debris layer was formed by a volcanic eruption, as some had speculated.

“A projectile originating in the outer region of the solar system sealed the fate of the dinosaurs,” said Mario Fischer-Gode, a geochemist at the University of Cologne in Germany and lead author of the study. Published on Thursday In the journal Science,

The impact at the end of the Cretaceous period left the Chicxulub (pronounced chick-shoo-loob) crater, 180 km wide and 20 km deep. The clay layer is rich in metals such as iridium, ruthenium, osmium, rhodium, platinum and palladium that are rare on Earth but common in asteroids.

The researchers focused on ruthenium — specifically, on the ratio of its isotopes present in the clay layer. Isotopes are atoms of the same element that have slightly different masses because of varying numbers of subatomic particles called neutrons. Ruthenium has seven isotopes, three of which are particularly important in the findings. The ruthenium isotope ratio matches that of other known carbonaceous asteroids.

“Ruthenium is particularly useful in this context, because the isotopic signature in the clay layer is almost entirely composed of ruthenium from the impactor, not from background sediments, and ruthenium shows different isotopic composition between inner and outer solar system materials,” said Steven Goderis, a geologist at Vrije Universiteit Brussels in Belgium and co-author of the study.

C-type asteroids, some of the oldest objects in the Solar System, are the most common asteroid type, followed by the stony S-type asteroids and the rarer metallic M-type asteroids. Compositional differences among asteroids arise from how far from the Sun they formed.

“C-type asteroids represent the leftover building blocks of the gas and ice planets of the outer solar system, while S-type asteroids are the primary building blocks of terrestrial planets like Earth in the inner solar system,” Fischer-Goode said.

After forming in the outer solar system, the asteroid probably later moved inward to become part of the main asteroid belt between Mars and Jupiter, and was possibly somehow accelerated toward Earth by a collision, Fischer-Goode said.

“All meteorites that fall to Earth, which are fragments of both C-type and S-type asteroids, originate from the asteroid belt. So it seems that the (end-Cretaceous) impactor also originates from the asteroid belt,” Fischer-Goode said. “But there are also many bodies stored in the Kuiper Belt and the Oort Cloud (the region far beyond the outermost planet Neptune), and basically not much is known about the composition of these bodies.”

The researchers analyzed samples from five other asteroid impacts, dating between 37 million and 470 million years ago, and found they were all S-type, reflecting the rarity of carbonaceous asteroid strikes.

Dinosaurs ruled this land for a long time, but except for their bird lineage, they were all wiped out after this impact, along with flying reptiles called pterosaurs, large marine reptiles, and other marine life including many marine plankton species.

Mammals overcame this, allowing these hairy creatures to eventually dominate the land and setting the stage for the emergence of our species about 300,000 years ago.

“I think that without this cosmic coincidence of the asteroid impact, life on our planet would likely have evolved very differently,” Fischer-Goode said.