Everything Everywhere Daily: History, Science, Geography & More - The Chicxulub Impact: The Asteroid That Killed the Dinosaurs

Starting point is 00:00:00 Around 66 million years ago, a meteorite smashed into what is today the Yucatan Peninsula of Mexico. The impact of that event changed life on Earth in ways that are still evident today. Proof of this impact, however, wasn't obvious. There was strong skepticism when the theory was proposed, and it took decades for it to become widely accepted. But in the end, the evidence proved overwhelming. Learn more about the Chicksilube impact, how it was discovered and how it changed the world. on this episode of Everything Everywhere Daily. Do you ever climb into bed ready to sleep only to have your mind start racing the moment your head hits the pillow?

Starting point is 00:00:49 Thoughts bouncing around, replaying the day or jumping ahead to tomorrow? That is exactly why Catherine Nikolai created Nothing Much Happens. Each episode is a gentle, cozy bedtime story where, well, nothing much happens. No drama, no tension, nothing you need to follow closely. Just soft narration, calming repetition, and soothing sensory details designed to help your mind slow down and your body relax. It's not about entertainment, it's about rest. And millions of listeners around the world use it every night to quiet their thoughts and

Starting point is 00:01:19 finally fall asleep. If you've ever struggled to shut your brain off at night, this might be exactly what you've been missing. You can listen to Nothing Much Happens wherever you get your podcasts. Episodes are every Monday and Thursday. About 66 million years ago, an asteroid roughly 12 kilometers or 7.5 miles in diameter, struck the earth at what is now the Yucatan Peninsula, creating, the Chicksilube crater. It hit at a speed of around 20 kilometers or 12.5 miles per second,

Starting point is 00:01:54 releasing energy equivalent to billions of nuclear bombs. The impact excavated a crater about 180 kilometers or 110 miles wide and temporarily tens of miles deep, making it one of the largest known impact structures on planet Earth. This is the largest single event to have occurred on the planet over the last several hundred million years. Evidence for something this big and incredible should be very obvious, but it isn't. Millions of years of geologic activity haven't left a giant obvious hole in the ground. The discovery of the impact was a process that took decades and actually started in the 19th century. In the 19th century, geologists mapping rock layers in Europe realized that fossils changed dramatically

Starting point is 00:02:44 between certain strata. In older rocks, especially those from the Cretaceous period, there were abundant fossils of dinosaurs, ammonites, and other now extinct organisms. In the layers above, then known as the tertiary or now known as the paleogene, those species were gone, replaced by entirely different forms of life. This abrupt turnover was so consistent worldwide that it became a formal boundary in the geologic time scale. However, early geologists assume that the change represented gradual transition over a long period, not a sudden event. This belief stemmed from the doctrine of gradualism in geology. Gradualism is the idea that the Earth's features are shaped by slow, continuous processes, acting over vast spans of time,

Starting point is 00:03:33 rather than by sudden catastrophic events. It was developed in the late 18th and early 19th century, most notably by James Hutton and later popularized by Charles Lyle, as a re-eastern. action against earlier beliefs that landscapes were formed primarily by short-lived dramatic events. By observing processes such as erosion, sedimentation, and volcanic activity in the present, these thinkers argued that the same processes acting slowly over millions of years could explain the formation of mountains, valleys, and rock layers. Gradualism isn't wrong. In fact, most of the geological phenomenon that we observe results from very gradual processes, such as, as mountain building or continental movement.

Starting point is 00:04:17 If you remember back to my episode on Jay Harlem-Bretz, he was a geologist from eastern Washington state who proposed that the geologic formations there weren't created by gradual processes, but rather by a sudden violent catastrophe. The doctrine of gradualism was so strong that most geologists couldn't accept anything other than a gradual process creating the Washington scablands. It took decades,

Starting point is 00:04:43 but eventually Brett's was vindicated, and the geology community came to accept that, while gradualism is usually true, sometimes there are exceptions. During the 20th century, geologists began a more focused study of the K-PG boundary, the rock layer that I previously mentioned that separates the Cretaceous and Paleogene periods. In many places around the world, the transition between these two periods in the rock strata was marked by a very thin layer of clay, often just a few centimeters thick. Below the layer, fossils of Cretaceous life were common, and above it, they disappeared. The thinness of the layer suggested that whatever happened occurred over a very short span of time on geological time scales,

Starting point is 00:05:29 which was difficult to reconcile with a slow gradual extinction. The turning point came in 1980 with the work of the father-son team, Lewis and Walter, Alvarez. Louis Alvarez had won the Nobel Prize in physics in 1968. His son Walter was a geologist at the University of California, Berkeley. While studying limestone sequences near Gubio, Italy, they analyzed the boundary clay and found unusually high eridium concentrations. This was shocking because iridium is relatively rare in the earth's crust, and there was no reason why one particular strata would contain so much eridium. While aridium is rare on Earth, it's relatively common in meteorites.

Starting point is 00:06:15 They concluded that the layer likely formed from material deposited after a massive extraterrestrial impact. What made this finding so compelling was that the same aridium-rich layer was soon identified at sites all over the world, indicating a global, not regional event. At the same time, while all this was happening, paleontologists were compiling increasingly, increasingly detailed fossil records, particularly in places like the Hell Creek formation in the Upper Great Plains. These studies showed that many species did not gradually decline over millions of years, but instead disappeared abruptly right at the boundary. Dinosaurs, which had dominated terrestrial ecosystems for over 150 million years, were present right up to the boundary and then

Starting point is 00:07:05 vanished entirely above it. The same pattern appeared in marine environments, where groups such as as ammonites and many plankton species disappeared suddenly. Additional evidence strengthened the case. Scientists found shocked quartz, tiny glass sphericals formed from molten rock and soot layers consistent with widespread fires, all concentrated at the thin clay boundary layer. These were all signatures of a massive high-energy event. So if this impact took place, the big question now was, Where on earth did it take place?

Starting point is 00:07:43 Researchers began by mapping the area with the thickest fallout. Layers of the K-PG boundary containing ejecta, such as glass sphericals and shocked minerals, were found to be especially abundant and coarse in the Caribbean region and along the Gulf Coast of North America, suggesting that the impact site was nearby. In places like Texas, Haiti, and Mexico, the boundary deposits were not just a thin clay layer,

Starting point is 00:08:10 but thick chaotic sediments consistent with tsunami backwash and nearby debris, further narrowing the likely region. At the same time, geophysicists revisited data collected by the Mexican oil company Pemex during petroleum exploration in the Yucatan Peninsula. In the late 1970s, they had identified a large circular pattern of gravity and magnetic anomalies beneath the surface near the town of Chixilube, along with a ring of sinkholes known as sonotes, that traced a buried circular structure. At the time, these features were not widely interpreted as an impact crater,

Starting point is 00:08:48 and much of the data remained internal to the company. In the early 1990s, geologists such as Alan Hildebrand connected these two threads. By comparing the geographic distribution of impact debris with the location of the geophysical anomaly, they realized that the Yucatan structure had exactly the right size, shape, and age to be the missing crater. Drilling into the site provided decisive confirmation. Core samples revealed shock to quartz,

Starting point is 00:09:18 melted rock, and breckias, all hallmarks of a large impact event formed under extreme pressure and temperature. Radiometric dating showed that these rocks formed at the same time as the K-PG boundary. What made the identification compelling was the convergence of independent evidence. The chemistry of the boundary

Starting point is 00:09:40 layer pointed to an extraterrestrial source. The distribution of debris pointed to the Gulf of Mexico region, and the buried circular structure beneath the Yucatan provided a physical crater and the correct age and scale. Together, these lines of evidence transformed the impact hypothesis from just an idea into a confirmed explanation, with the Chixilube crater serving as the long-sought site of the event that ended the age of the dinosaurs. So, you'd think you'd saying, with so much independent evidence, convincing the rest of the scientific world would have been a slam dunk. But it wasn't. The difficulty in accepting the impact hypothesis wasn't about a lack of evidence so much as it was about how radically it changed the way geologists and paleontologists

Starting point is 00:10:27 thought the Earth worked. The assumption of gradualism was still very strong. When Lewis and Walter Alvarez proposed that a single asteroid impact caused the extinction at the K-P boundary. Many scientists were instinctively skeptical because it sounded like a return to catastrophism, which the field had spent generations moving away from in the 18th and 19th centuries. There were also legitimate scientific objections. Critics pointed out that no crater had been identified where the Alvarez's made their claim, which was a major shortcoming. Others argued that extinctions in the fossil record might not be as sudden as they appeared and could reflect incomplete data or gradual environmental stress.

Starting point is 00:11:11 Many researchers favored alternative explanations, especially massive volcanism from the decon traps in India, which could have altered the climate over a long period of time. In addition, some paleontologists felt that dinosaur extinction patterns were more complex than a single instantaneous event could possibly explain. Throughout the 1980s, the debate was intense and often divided among disciplinary lines. Physicists and geochemists tended to support the impact hypothesis because of the eridium evidence and physical modeling, while many paleontologists

Starting point is 00:11:43 and geologists remain cautious or opposed the idea. The turning point came in the early 1990s with the identification and confirmation of the Chixilube crater. But even then, acceptance was not instantaneous. Throughout the 1990s, debate continued about whether the impact was the sole cause or one contributing factor. But by the late 1990s and early 2000s, a broad consensus had formed that the Chixilube impact was the primary driver of the K-PG extinction, even if other factors like volcanism may have played a supporting role. In total, it took roughly 10 to 15 years from the publication of the Alvarez hypothesis in 1980 to the early 1990s for the idea to move from controversial to widely accepted,

Starting point is 00:12:31 and closer to two decades for it to become the dominant explanation taught and referenced across the scientific community. So now that we have several decades of data under our belt, what is the current explanation for what exactly happened? At the start of the episode, I gave you the estimated size and speed of the meteorite when it hit the earth. The immediate regional effects of the impact were almost unimaginable. The shockwave would have flattened forests across much of North America, while earthquakes, far stronger than any ever recorded in history rippled around the globe. The impact site, which was a shallow sea at the time, generated colossal tsunamis that swept across the Gulf of Mexico and into

Starting point is 00:13:18 surrounding coastlines. Debris ejected into space began falling back to Earth within minutes to hours, reintering the atmosphere at high speeds and heating it to the point that much of the planet's surface experienced intense thermal radiation. This likely ignited widespread and and possibly global wildfires. The longer-term events were even more consequential. The impact blasted enormous quantities of dust, ash, and sulfur-rich gases into the atmosphere. Because the target rocks contained large amounts of sulfur, the collision produced sulfate aerosols that reflected sunlight back into space very efficiently.

Starting point is 00:13:59 Within days to weeks, sunlight reaching the Earth's surface dropped dramatically. Temperatures plunged in what's often described as, as an impact winter, with some models suggesting global surface temperatures fell by more than 10 to 20 degrees Celsius. Photosynthesis collapsed almost immediately because of the lack of sunlight. And this was the crucial turning point. Plants on land and photoplankton in the oceans form the base of most food chains, and when they fail, entire ecosystems start to unravel. Erbivores died first, followed by carnivores that depended on them. In the oceans, food webs collapsed from the bottom up, devastating marine life. The speed of these changes is one of the most

Starting point is 00:14:41 striking aspects of the event. The initial devastation near the impact occurred within minutes to hours. The atmospheric heating and wildfires likely unfolded within hours to days. The collapse of photosynthesis and the onset of global darkness happened within days to weeks. Mass starvation and ecosystem collapse followed over weeks to months, with the majority of extinctions occurring within a relatively short geological window, possibly a few years to decades. In total, about 75% of the Earth's species went extinct. All non-avian dinosaurs disappeared, along with many marine reptiles, ammonites, and a large fraction of plant and plankton species. Smaller animals, especially those that could burrow, live in water, or survive in limited

Starting point is 00:15:28 resources had a better chance of surviving. Over time, the dust and aerosols settled out of the atmosphere and sunlight gradually returned. However, the biosphere that reemerged was totally different. The extinctions opened up ecological niches that allowed mammals and eventually birds, the descendants of surviving dinosaurs, to diversify and dominate the planet. The Chixilube impact didn't just end the age of dinosaurs. It reset the trajectory of life on earth, setting the stage for the world that we live in today. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Otkin and Cameron Kiefer.

Starting point is 00:16:15 My big thanks go to everyone who supports the show over on Patreon. Your support helps make this podcast possible. And I also want to remind everyone about the community groups on Facebook and Discord. That's where everything happens that's outside the podcast. And links to those are available in the show notes. As always, if you leave a review on any major podcast app, or in the above community groups, you two can have it read in the show.

Everything Everywhere Daily: History, Science, Geography & More - The Chicxulub Impact: The Asteroid That Killed the Dinosaurs

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