When a massive space rock slammed into Earth 66 million years ago, it wiped out vast swaths of life and ended the reign of the dinosaurs. Now scientists say they have new insights into what it was made of.
Experts studying the material deposited at the time of the event say they have found clear signs supporting the idea that the Chicxulub impact crater was created by a carbon-rich, C-type asteroid that originally formed outside the orbit of Jupiter.
Mario Fischer-Goud, co-author of the study from the University of Cologne, said the team is now keen to look at sediments associated with the impact that some suggest was behind it. A major extinction occurred about 215 million years ago..
“Perhaps this way we can learn whether C-type asteroid impacts have a higher probability of causing mass extinction events on Earth,” he said.
Writing in Science MagazineThe researchers report how they studied different types, or isotopes, of ruthenium within a layer of material that settled over the Earth after the impact 66 million years ago.
“This layer contains traces of asteroid debris,” Fischer-Judy said.
The team chose to study ruthenium because the metal is very rare in the Earth’s crust.
“The ruthenium we find in this layer is almost 100 percent derived from the asteroid,” Fischer-Judy said, adding that this gives scientists a way to determine the composition of the object that hit Earth, and therefore what type it was.
The team found that samples of the layer from Denmark, Italy and Spain all showed the same ruthenium isotope composition.
The result is different from the composition generally found on Earth, which rules out the theory that the presence of ruthenium and other metals such as osmium and platinum is due to past Deccan Traps volcanic eruptions, Fischer-Judy said.
The team also questioned whether the object that struck Earth was a comet, saying the ruthenium isotope composition in the samples differed from that of meteorites, which are believed to be fragments of comets that lost their ice.
Instead, the ruthenium isotope results are consistent with the average composition of meteorites from carbonaceous (C-type) asteroids — carbon-rich space rocks that formed in the early solar system, beyond the orbit of Jupiter.
But questions remain about exactly where the asteroid came from before it headed for Earth.
C-type asteroids can be found today in the asteroid belt between Mars and Jupiter, because Jupiter migrated shortly after the solar system formed, scattering asteroids in the process, Fisher-Judy said.
As a result, it is suggested that the ill-fated space rock may have come from there.
“Maybe there was a collision between two asteroids in the belt, and then this piece went into orbit past Earth. That could be one scenario,” he said, although he noted other possibilities, including that it came from the Oort Cloud, which is thought to surround the solar system.
Dr Craig Walton of the University of Cambridge, who was not involved in the work, said the research was interesting although in his view it was still unclear whether the object that struck Earth was an asteroid or a comet.
“However, this kind of work gives us more detailed insights into the nature of the bodies that have shaped Earth’s history so dramatically,” he added.
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