The object that hit the earth 66 million years ago and triggered the extinction that almost all dinosaurs triggered was an asteroid that originally arose beyond the orbit of the Jupiter, so Geochemian evidence from the impact location in Chicxulub, Mexico.

The one on August 15th in science 1 A series of events began at the birth of the solar system. Scientists had long suspected that the chicxulub impactor, as it is known, was an asteroid from the outer solar system, and these observations support the case.

The chalk paleogen (K/PG) was the fifth in a series of mass extinction that has occurred over the past around 540 million years: the time when animals have spread on earth. The event deleted more than 60% of the species, including all non-bird-like dinosaurs.

Since 1980, evidence has accumulated that extinction was caused by a city -sized object that hit the earth. Such an impact would have enormous amounts of sulfur, dust and soot thrown into the air , some of which blocked the sun and led to a crash of temperature. A layer of rare iridium metal, which is rare on earth, but is more common in asteroids, was deposited around the world at the beginning of extinction. In the 1990s, scientists 2 the impact location near chicxxulub on the Mexican Peninsula Yucatán.

"We wanted to identify the origin of this impactor," says Mario Fischer-Gödde, an isotope geochemist at the University of Cologne in Germany. To find out what it was and where it came from, he and his colleagues wandered samples from K/PG rocks from three locations, and compared them with rocks of eight other impact points from the past 3.5 billion years.

ruthenium signature

The team focused on the isotopes of the ruthenium metal. Ruthenium is extremely rare in earth rocks, says Fischer-Gödde, which is why samples from an impact location "The pure signature" of the impactor offer. There are seven stable isotopes of ruthenium, and the celestial body have characteristic mixtures of them.

In particular, the consideration of ruthenium-isotopes can help a distinction between asteroids that have arisen in the outer solar system-beyond the orbit of the Jupiter-and which with an origin in the inner solar system. When the solar system was formed from a molecular cloud about 4.5 billion years ago, the temperatures in the inner region were too high for fleeting chemicals such as water to condense. As a result, asteroids that were created there had low amounts of volatility, and became rich in silicate minerals. Asteroids that emerged further outside became "coal oak", contained a lot of carbon and fleeting chemicals. The ruthenium isotopes were unevenly distributed in the cloud, and this heterogeneity has been preserved in asteroids.

The Fischer-Gödde team found that the Ruthenium isotopes in the chicxulub impactor fit well with a coal-rich asteroid from the outer solar system and not to silica-rich asteroids from the inner solar system.

Earlier studies have also indicated that the impactor was a coalic asteroid, says Sean Gulick, a geophysicist at the University of Texas in Austin. But the latest work "is a really elegant way to get to some of these answers and get several of the same answers with a methodology," he adds.

not a comet

The ruthenium isotopes also provide information against another hypothesis: that the chicxulub impactor was a comet and was not a asteroid. "The idea that it was a comet goes far back into literature," says William Bottke, a planetary researcher at the Southwest Research Institute in Boulder, Colorado. The hypothesis was revived in a controversial study of 2021 3 Long -term comet was, which had broken under the gravitational influence of the sun.

But Fischer-Gödde says that the Ruthenium isotope data did not fit a comet. Gulick agrees. He adds that geochemical evidence of the chicxulub impact location never agreed with a comet, and the latest study "really contributes to clarifying".

Bottke adds that the comet hypothesis also "encounters difficulties" when you look at the dynamics of the solar system. "Significant coal -rich asteroids are more likely to meet the earth than comets," he says. In a study of 2021, he and his colleagues argued that the impactor probably came from the main seaside belt between Mars and Jupiter.

Most other impactors that the Fischer-Gödde team examined seem to have emerged according to their ruthenium isotopes in the inner solar system. The only exceptions were the oldest from the time between 3.2 billion and 3.5 billion years that looked more like the chicxulub impactor. It could be that "something interesting in the asteroid belt passed at this time, such as breaking a large asteroid in a good place to bring objects to earth," says Bottke.