In 1825, George Cuvier, a zoologist deemed the “founding father of paleontology,” first observed a mass extinction of animals between the Mesozoic and Cenzoic eras. In the rock records, there was no evidence of dinosaurs above the K-Pg boundary, formerly known as the Cretaceous-Tertiary (K-T) boundary layer. The K-T boundary is the transition and abbreviation for the Cretaceous period and Tertiary period. At and below the KT boundary, dinosaur fossils could be found. Above the KT boundary, there were no more dinosaur fossils which meant dinosaurs went extinct. What caused this mass extinction? Was it a super volcano or volcanos? There were no human eyewitnesses or recorded accounts of what had happened. Humans did not exist at this time, but we can learn a great deal about Earth’s history, because it is recorded in rocks. Geologists find that most changes in the Earth history have taken place slowly and gradually, but there are a few occasions when the Earth has suffered sudden enormous catastrophes.
It is tough to appreciate how difficult it was to find the answer to how the dinosaurs and most living creatures disappeared about 66 million years ago. We all know the answer now, just like we know that mosquitoes transmit the parasite Malaria. Try to imagine it another way – what causes Dementia? We still don’t know the answer to this. Yes, there are some theories, but no definitive answer. This will give you an appreciation for how difficult it is to find an answer to a scientific mystery.
Walter Alvarez, a geologist and a professor in the Earth and Planetary Science department at the University of California, Berkeley, Luis Alvarez (Walter Alvarez’s father), also a professor at U.C. Berkeley and recipient of the Nobel prize in physics, Frank Asaro, a nuclear chemist at Lawrence Berkeley National Laboratory and Helen Michel, chemist at Lawrence Berkeley National Laboratory were investigating a possible explanation. Naturally, Walter Alvarez studied the geology – the KT boundary in search of an answer to what led to the mass extinction event.
The team looked at the iridium, the most corrosive-resistant material known, and a rare metal in the platinum group that was found in the clay of the KT boundary where dinosaur fossils were last found. Iridium is more concentrated in meteorites than on Earth. The concentration of iridium in the KT layer was about 9 parts per billion. This may seem like an extremely small number, but it is thirty times larger than the average value of 0.5 parts per billion found on Earth. Some types of meteorites contain as much as 500 parts per billion of iridium. Iridium and all other elements heavier than iron were originally created in supernova explosions.
At first the team did not think it was an asteroid or comet that caused the mass extinction, since an impact would cause devastation, but in a limited area surrounding the impact, not a worldwide event. Maybe it was a supernova explosion? However a supernova explosion would have showered the earth with plutonium 244 with a half-life of 8.3 million years. Plenty of it should still be around after 66 million years. Analysis of the KT boundary found no plutonium.
The impact of a multi-kilometer asteroid could have distributed iridium-rich dust all over the Earth. Other evidence pointed to an asteroid impact. At the KT boundary, there was shocked quartz which indicated very high pressure. Impact melt droplets were also found in the KT boundary. Alexander Shukolyukov and Gunter Lugmair, researchers from the Scripps Institution of Oceanography, reported extraterrestrial amino acids at the KT boundary.
Walter Alvarez, Luis Alvarez, Frank Asaro and Helen Michel wrote a paper, “Extraterrestrial cause for the Cretaceous-Tertiary Extinction,” in the journal Science, in 1980 detailing how the Earth’s history recorded in rocks told the story of how the dinosaurs went extinct.
In the 1980’s the KT debate was polarized between those scientists who thought the KT mass extinction event was the result of volcanos, and those who thought it was from an asteroid impact. Some evidence existed for the volcanos theory. A massive volcanic eruption fed by a deep magma chamber that had iridium from the lower mantle might have injected enough dust into the atmosphere to block sunlight and cause the dinosaurs to die out. Scientists from the Lawrence Berkeley Laboratory measured concentrations of iridium and similar metals (ruthenium and rhodium – both in the platinum group) in the KT boundary and found that the relative proportions of these elements were approximately the same as in chondritic meteorites and very different from those in volcanic emissions.
There was still a crucial missing piece for the impact hypothesis – where was the crater that would have existed from such a devastating mass extinction event?
Canadian geologist, Alan Hildebrand, a PhD candidate at the University of Arizona, decided the Brazos River tsunami bed was key to finding the crater. He reasoned that the impact crater was somewhere between Texas and Columbia, because the Gulf of Mexico is an enclosed body of water protected from distant tsunamis. He knew the tsunami had to come from south of Texas, since that was where deep water was 65 million years ago. If the impact had been in the ocean, tsunamis would have carried the sediments and impact glass from the impact site to other coastal areas. This is the reason that the impact did not occur on land. He found tsunami evidence in the KT boundary in Haiti.
Antonio Camargo, geologist, and Glen Penfield, geophysicist, working for Petroleos Mexicanos (PEMEX), the Mexican national oil company, identified an impact crater on the Yucatan Peninsula in Mexico while searching for oil. Their work was published as an abstract of a meeting of the Society of Exploration Geophysicists, but the Berkeley team was unaware of their work. The work of oil company geologists would not normally be published in a widely available science journal, since their work is confidential.
In 1991, Alan Hildebrand, et al wrote, “Chicxulub Crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico” in the journal Geology. The impact crater was dated about 65 million years in age. The crater is between 180 and 300 kilometers (112 – 186 miles) in diameter, making it the largest impact crater on Earth. This discovery confirmed what the Alvarez team had theorized, that an asteroid or comet struck our planet about 65 million years ago causing a mass extinction event.
The remaining question I had was it an asteroid or comet that struck our planet causing the mass extinction event? I posed this question to my friend, retired Adjunct Professor and present curator of the UCLA meteorite collection, Dr. Alan Rubin, and his response was as follows: “Comets have been described as dirty iceballs or icy dirtballs. In either case, their concentration of Ir would be lower than in meteorites. But two things: the date is now about 66 Ma, not 65. Also, some years ago, Frank Kyte found a 2.5 mm carbonaceous chondrite fragment in a deep-sea drill core exactly at the depth of the Ir anomaly. To me, this is very likely a piece of the projectile that wiped out the non-avian dinosaurs. That means, of course, it was not a comet, but instead was a 10-12 km carbonaceous chondritic asteroid. The Cr isotopic ratio at the boundary also matches that of carbonaceous chondrites.”
Since evidence points to a carbonaceous chondritic meteorite, then it makes sense that Alexander Shukolyukov and Gunter Lugmair, researchers from the Scripps Institution of Oceanography reported extraterrestrial amino acids in the KT boundary. The late Dr. Carleton Moore explained to me that amino acids contained in carbonaceous meteorites, such as Murchison (Australia), did not bring life to our planet, but that amino acids are the building blocks of life and make life possible.
It is difficult for us to comprehend the mass extinction event of an asteroid colliding with the Earth since the extreme event is far beyond our life experience. The asteroid was about 15 kilometers (9 miles) in diameter and the size of a mountain. What turned it into a mass extinction weapon was its velocity – 43,000 km (27,000 miles) per hour. A fighter jet’s top speed is about 1,500 miles per hours (2,414 km/hour). The speed of sound is about 767 miles per hour (1,235 km/hour). It would take a fighter jet at top speed over 16 hours to circle the Earth (if it did not have to refuel). The Chicxulub meteor could circle the Earth in a little over half an hour. A bullet fired from a gun (depends on the gun) travels about 3,000 feet per second (about 2,045 mph or 3,292 km per hour) and the Chicxulub meteoroid was traveling more than twelve times faster than a speeding bullet.
Scientists released a record of the day of chaos in the Proceedings of the National Academy of Sciences on the Chicxulub mass extinction event. Let’s go back in time, 66 million years ago, when the dinosaurs roamed the Earth. At the time of Chicxulub’s impact, a mountain-size asteroid is rocketing towards Earth at thirty-five times the speed of sound. It sped through Earth’s 60 mile (97 km) atmosphere in three seconds and causes sonic booms heard on all continents. It struck the shallow waters of the Yucatan Peninsula in Mexico. Any animals that could see the asteroid hit would have been vaporized instantly. No land animals larger than 55 pounds (25 kg) would survive after Chicxulub’s impact and nuclear winter. The friction of the impacts causes immense heat and releases energy equivalent to more than one billion Hiroshima atomic bombs. The release of energy heats molecules to far hotter than the surface of the sun. The impactor is vaporized. The impact shockwave forms a blast wave of pressure outwards at more than 1,000 mph (1,600 km per hour) vaporizing anything in Texas and deafening animals in New York. The Chicxulub impact would cause powerful shock waves vibrating through the Earth’s crust and triggering fault-slipping earthquakes across our planet. Any living thing on the other side of the planet would feel the ground shake for 30 minutes. The impact triggers tsunamis 1,000 feet tall hitting coastlines in Mexico and the southern U.S.A., and flood tens of miles inland. Tsunamis 600 feet tall hit the coasts of the eastern U.S.A, Europe and Africa. Fifteen hours after impact, all coastlines on Earth are hit with tsunamis. When the tsunamis retreat, they suck living creatures back into the ocean. When the asteroid strikes, its impact sends 25 trillion tons of earth at speeds exceeding Earth’s escape velocity. Most of the debris returned back to Earth. The rocks and boulders come back killing or injuring all wildlife they strike. As the debris falls their friction with the atmosphere emit enough thermal radiation to set fires across the Earth. Most of the trees on our planet burn causing smoke that envelopes the planet. Chicxulub hit the oil-rich peninsula, vaporizing the oil and ejecting it towards the sky. The oil condenses in the stratosphere as a black sooty layer covering the Earth like a layer of black paint. The black soot is high above the cloud layer, so it does not rain back down. The soot layer reduces the amount of sunlight to reach our planet by up to 90% for at least two to three years. This is probably similar to the “nuclear winter” Carl Sagan talked about after a nuclear world war. This causes a deep and long lasting freeze. Global temperatures drop by an average of about 50 degrees. At this time, evaporation almost ceases causing rainfall to decrease by 80%. Most of our planet turns into a desert. There was a domino effect. The reduction in plant life had a huge impact on herbivores’ ability to survive, which in turn meant carnivores would also die off from not having enough food. Breeding seasons would have been shorter and conditions harsher. About 75% of all animals on the planet die. Numerous wildlife living in large bodies of water and various small land animals, including some mammals survive the catastrophic event. A new era is born.
Acknowledgement: I would like to thank Dr. Walter Alvarez (U.C. Berkeley) who patiently answered my many questions back in 2014. I would also like to thank my friend, Dr. Alan Rubin, (UCLA) whose insights and suggestions made this article more interesting than I could have imagined. A big thank you to my friend, Rob Wesel (Nakhla Dog Meteorites), for providing me with the outstanding photos for this article which brought the article to life. In addition, I would like to thank Dr. Tim McCoy (Smithsonian museum) for always promptly responding to my questions.
Emails from 2014 between Dr. Walter Alvarez and Mitch Noda
Emails between Dr. Alan Rubin and Mitch Noda
T.rex and the Crater of Doom, Dr. Walter Alvarez
Alvarez et al., Extraterrestrial cause for the Cretaceous-Tertiary Extinction.” Science. Volume 208, Number 4448, 1980
Disturbing the Solar System – Princeton University Press, Dr. Alan Rubin
Science: Updated: Drilling of dinosaur – killing impact crater explains buried circular hills, Eric Hand, 17 Nov. 2016
Lunar and Planetary Institute: Chicxulub Impact Event
Nature reviews earth & environment: The Chicxulub impact and its environmental consequences, Joanna V. Morgan, Timothy J. Bralower, Julia Brugger, Kai Wunnemann, 12 April 2022
YouTube: The First Minutes The Dinosaurs Went Extinct, Destiny
ScIU: How did we find out that an asteroid killed the dinosaurs? Nathan Roden, 8 April 2023