Asteroids, volcanic eruptions and poisonous plant species: the extinction of the dinosaurs has been a hotly debated topic for decades. But researchers have found hard evidence of an asteroid impact that had a massive effect on the Earth's climate along with asteroid-specific minerals like iridium at the crater in Chicxulub, Mexico, all but proving the asteroid theory.
And now scientists have figured out where the asteroid likely came from, and it wasn't from anywhere nearby. Research headed by Mario Fischer-Gödde at the University of Cologne in Germany says the asteroid came from beyond Jupiter, well into the outer portion of our solar system.
The research paper, published Thursday in the journal Science, identified it as a C-type asteroid. Known as a carbonaceous meteor, these most commonly come from the outer solar system. C-type meteors are exceptionally old, and their makeups can help researchers learn more about the early history of our solar system.
Learning where the meteorite came from
To figure this out, scientists had to go through a number of steps. When the meteorite smashed into Earth, it pulverized rock and launched it into the skies. This giant dust cloud -- which included material from both Earth and the meteorite -- lowered the temperature of Earth and wiped out most of the species in existence. That dust eventually settled, where it would become a layer of rock that scientists could dig up tens of millions of years later.
Geologists designate this very thin layer as the K-Pg layer, which describes the time when the Cretaceous period ends and the Paleogene period begins. It was around this time, 66 million years ago, when the asteroid was thought to hit.
Researchers dug up samples from the K-Pg layer and found ruthenium, an element that is rarely found on Earth but is plentiful on carbonaceous meteorites. The isotopes, or atoms, found in the ruthenium matched those found in ruthenium in other carbonaceous meteorites, proving that it came from a meteorite and not Earth.
To make sure, researchers also compared it to material found in other major meteorite impacts and found no matches. That means the ruthenium found in the K-Pg layer came from the same meteorite that hit Chicxulub.
How does this tie into the theory that an asteroid killed the dinosaurs?
As the theory goes, a 6-mile-wide meteor plunged into Earth near modern-day Chicxulub on the Yucatan peninsula. The impact launched vaporized rock and debris into the air, covering the planet in a dust cloud that caused the temperature to fall by about 50 degrees Fahrenheit (28 degrees Celsius). This caused a long winter that killed off nonavian dinosaurs, along with 70% of all life on Earth.
Eventually, the dust fell back to Earth where it became the K-Pg rock layer, and then other things got piled on top that also became rock. Whatever happened when the K-Pg layer was created definitely killed the dinosaurs, because no nonavian dinosaur fossils have ever been found above the K-Pg layer.
Researchers have found plenty of stuff in the K-Pg layer, including iridium and chromium. Iridium is rare on Earth but common on asteroids, so when they found iridium in the 1980s, it helped piece together the puzzle of what killed the dinosaurs. Chromium, by contrast, is very common on Earth so it could not be correlated to a meteorite impact.
Later, scientists found more evidence in the form of sulfur in the K-Pg layer but not in the impact crater, suggesting that the impact launched sulfur into the atmosphere, which certainly contributed to global cooling. Sulfur was found in the rock as far away as Antarctica, which showed how violent the meteorite impact was.
We now come to today. As Fischer-Gödde explained to Mashable, ruthenium is quite difficult to detect and it required some technological advancements to do it. So, the team measured five samples from the K-Pg layer and found that the ruthenium from all five samples likely came from the same single source. They also found that the isotopes matched those of carbonaceous meteorites that had been previously analyzed.
To sum it up: The meteorite that hit Earth and killed the dinosaurs was likely formed billions of years ago as part of the solar system's earliest history, and not something that was close by like most meteorite impacts.