On the trail of the Dino-Killer!

The dinosaurs ruled the Earth for almost 180 million years, yet almost all of them were wiped out in a just few thousand years. The mystery of what happened to this incredibly diverse and widespread class of animals puzzled the best scientists for generations, until Nobel Prize-winning physicist Luis Alvarez and his geologist son Walter Alverez published a theory that a layer of iridium-rich clay found around the world was in fact caused by a large asteroid colliding with Earth.

This controversial theory was gradually accepted as the evidence began to mount, that the mass-extinction of 75% of all life on earth was from an extraterrestrial cause. It is called the Chicxulub impact, and landed just off the coast of the present-day Yucatán Peninsula in Mexico. The explanation was dubbed the Alverez hypothesis, and accounted for many strange observations, like the presence of rock from deep within the earth near the surface in Yucatán, damage from giant tsunamis, and the rapid disappearance of many different lifeforms at once.

The asteroid hit at high velocity and instantly vaporized itself and the land, throwing a huge dark cloud of debris high into the atmosphere and spreading around the world. The impact site is still evident from space and the debris is found on all continents, including Antarctica! The high concentration of iridium is relatively easy to detect.

The clays are found as a thin layer in rock formations well known to geologists, and is considered the boundary between two geologic eras, called the K-Pg boundary layers. This geological evidence is approximately 66 million years old, and marks the end of the dinosaurs, the beginning of the rise of mammals, and after millions more years, we humans.

There are still questions to explore, like: Where did the dino-killer asteroid come from?

Now an international team of scientists say they have pinpointed the Chicxulub impactor’s origin and composition. The researchers reported in Science, on August 16, 2024, that it was a carbonaceous asteroid containing rocks, water, and carbon — essentially, just a big mudball from outer space with black crunchy bits in it. The asteroid came here, apparently, from beyond Jupiter.

On closer study, they found high levels of platinum-group elements (PGEs) such as iridium, ruthenium, osmium, rhodium, platinum and palladium in the K-Pg boundary layers. This is a geological signature, usually a thin band of rock containing much more iridium than other bands. These elements are rare on Earth, but they’re common in meteorites, or rocks from space. But where in space?

Fischer-Gödde and his colleagues studied the ruthenium (Ru) isotopes in samples taken from the K-Pg boundary. Isotopes are elements that have multiple versions, each with the same number of protons in their nucleus, but different numbers of neutrons. The number of neutrons are a clue to where those atoms were formed and their cosmic history. The team studied ruthenium isotopes in many asteroid impact sites around the world, and from different meteorite samples. Ruthenium is roughly 100 times more common in extraterrestrial rocks than those on Earth, making it a good marker.

The results showed that the ruthenium isotope signatures in the clay were uniform and closely matched those of carbonaceous chondrite meteorites, but did not match other meteorites or rocks from any place on earth. Carbonaceous asteroids are believed to have formed in the outer solar system.

Fischer-Gödde said:

“The asteroid’s composition is consistent with that of carbonaceous asteroids that formed outside of Jupiter’s orbit during the formation of the solar system.”

Carbonaceous chondrites are remnants from the Solar System’s earliest days, 4.6 billion years ago, not long after the Sun coalesced from a gigantic cloud of interstellar gas and dust. They’re rich in water and carbon, different from earth-like rocky asteroids, yet the Chicxulub impactor fell fairly recently in geologic time. “How do we explain why Chicxulub would be of this type of meteorite found further from the Sun?” asks Simone Marchi of the Southwest Research Institute in Boulder.

Simulations he and his colleagues made might hold an answer. Carbonaceous chondrites are thought to orbit in the outer part of the asteroid belt between Mars and Jupiter, after being herded there by the giant planets. The asteroids are leftovers from the early solar nebula, that gradually drifted closer to the Sun via gravity from Jupiter. The simulations from Marchi and colleagues showed how further gravitational kicks from the giant planets Jupiter and Saturn could occasionally knock carbonaceous asteroids loose from the belt and send them hurtling towards the inner Solar System. They found that Chicxulub-size asteroids, about 10 kilometers wide, would be ejected from this region and set on Earth-intercepting orbits every few hundred million years.

The Dino-killer was responsible for a horrible mass extinction, yet eventually made human life possible. To prevent our own destruction by a giant meteor, we have developed and tested planetary defense.

Keeping Earth Safe (as best we can)

The NASA Planetary defense coordination office, established in 2016, was created to manage the agency’s ongoing mission of finding, tracking, and better understanding asteroids and comets that could pose an impact hazard to Earth. Here you can stay informed about the PDCO, NASA’s Near-Earth Object (NEO)  Observations Program, and upcoming planetary defense flight missions, including NASA’S NEO Surveyor mission.

The office does its best to identify potential threats similar to the one that ended the dinosaurs and plot the probably trajectories of each instra-system object. So far, it hasn’t detected any on a direct collision course with Earth, though there have been a few near misses, like the one about the size of a truck that passed 2,200 miles over the southern tip of South America in 2023. The near misses detected so far have all been pretty small by comparison to the Chixulub meteor. Obviously we’re hoping it stays that way for the foreseeable future, but if they do detect a big one, we may have enough advance notice so that we might be able to do something about it. The fact that we now have a pretty good idea of where the Chixulub meteor came from gives us a fighting chance.