Geologists recognize five major extinction events since life emerged on our planet. Each of these catastrophic periods wiped organisms from Earth, usually to the tune of more than 75% of all living species at the time. One such occasion, the Permian–Triassic extinction event, eliminated between 90-96% of species from existence!

The one most people probably know best is called the Cretaceous–Paleogene extinction event. This occurrence created what we sometimes call the K-T boundary. You might not recognize these specific names, but you almost certainly know the result: this extinction event ended the reign of (non-avian) dinosaurs. It happened just over 66 million years ago and is the most recent major extinction event.

Since the discovery of dinosaur fossils, scientists had wondered and speculated on the cause of their demise. Various large-scale culprits emerged as possibilities. Some espoused extraordinary volcanic eruptions that altered the climate quickly; others wondered if less cataclysmic, yet widespread, volcanic activity led to a gradual problem with sunlight and food chains; some scientists believed a natural climatic change occurred; still, others assumed a massive comet or asteroid struck the planet, quickly ending most life. Today, nearly all scientists subscribe to the latter theory. The Cretaceous-Paleogene extinction event was most likely the result of an extraterrestrial body slamming into Earth.

But the story of how we arrived at that consensus reads like a scientific mystery novel!

Erosion in badlands in Canada exposes the K-T boundary in the rock - photo by G Larson

The sudden disappearance of large dinosaurs and a worldwide layer of iridium prompted many paleontologists to jump on the comet/asteroid bandwagon. The iridium seemingly existed all across the orb at levels 160 times normal. The coating lay in the right timeframe for the extinction event, too. This metallic paint job almost certainly pointed to a tremendous blow.

A few problems persisted with the theory, however. If a gigantic rock had slammed the planet, where was the impact crater? Something large enough to eradicate 75% or more of the species on Earth would likely have produced one of the largest impact craters in the planet’s history. Second, scientists became extremely good at exploring the fossil record. We comprehensively cataloged the layers of rock and sediment across the planet, piecing together a geological and biological record of the past. Yet, dinosaur fossils from the precise period of the extinction event were curiously absent.

Many waved away the first problem – the impact crater – thanks to the geography of Earth: we’re mostly water. The vast oceans could easily hide a large crater. However, the lack of fossils in the proper zones prompted some researchers to completely discount the impact notions. Without a significant discovery, scientists resigned themselves to the potential of never knowing what really caused the dinosaurs to disappear.

The Yucatan Peninsula - graphic by Kaldari

In 1978, two geophysicists found themselves on the Yucatan Peninsula. Glen Penfield and Antonio Camargo worked for Pemex, a Mexican state-owned oil company. Their jobs were to use geophysical data to locate new spots to drill. Penfield scoured offshore magnetic data and noticed an incredible anomaly. He then grabbed gravity information for the peninsula. When he combined the data, Penfield couldn’t believe what popped out. A 110-mile “bullseye” emerged on the maps, partially on land and partially in the water. To Penfield, this circle denoted only one thing: an impact crater.

He had a big problem, though. Pemex policy forbade the publication of corporate data. As it turns out, a decade earlier, a contractor named Robert Baltosser had arrived at the same conclusion. But scientists never received the information due to the confidentiality clauses. Penfield presented his findings to the company, which immediately repudiated the idea. Pemex believed the data pointed to volcanic activity, instead. Perhaps because of this belief, they actually allowed Penfield and Camargo to present the general theory, without specific data, to the Society of Exploration Geophysicists in 1981.

Unfortunately, the gathering was poorly attended. Ironically, many of the world’s top geophysicists had foregone the conference in order to visit another assemblage. In June 1980, a group of scientists published a paper on the iridium abnormalities we discussed earlier. Around the world, scientists tested the rocks and corroborated the anomaly. Two geophysicists decided to wrangle the world’s top geological talent in an attempt to crowdsource the discovery of the impact crater that must have created the iridium spike. They all gathered in Utah during Penfield’s presentation.

The information the group sought was presented the very same week they convened in a nearly empty lecture hall. In the days before the internet, Penfield and Camargo’s message went largely unheard. Penfield had the information, but he had no rock samples to back up his claims about an enormous impact crater. Despite his vociferous advocations, his theory gained almost no traction. Unable to get the company to drill deeply enough for new samples, Penfield decided to move on.

Glen Penfield

In the ensuing years, a University of Arizona graduate student named Alan Hildebrand and his advisor searched for a crater in Texas. They had discovered some clay with excess iridium, shocked quartz, and glass beads, called tektites. These attributes were telltale signs of an impact. They were certain a crater would be nearby. Meanwhile, a professor in Haiti found what he thought was evidence of an ancient volcano. Hildebrand analyzed the information and realized the Haitian volcano might actually be more evidence of an impact in the Caribbean region. Scientists dug into the K-T boundary and discovered tektites there, too. Tektites come from two possible things: asteroid impacts and nuclear detonations. Hildebrand knew he was onto something.

In 1990, a colleague mentioned to Hildebrand a theory he had heard a decade earlier. Realizing that the crater he sought might be an even more outlandish happening than he previously realized, Hildebrand contacted Glen Penfield about his crater in the Yucatan Peninsula. Tag teaming the situation suddenly opened some doors. Penfield had been unable to obtain Pemex rock samples in 1980, but the pair discovered that rocks from previous digs had somehow been stored in New Orleans for decades. The duo managed to obtain the samples. Hildebrand tested the rocks, which had all the markers of a gargantuan impact.

Scientists then went to the air. Satellite images showed rings, just as Penfield had claimed. One of the circles centered on the town of Chicxulub Puerto. Penfield decided to name the crater for the town, partially to make it hard for all the people who had doubted his theory to pronounce. The Chicxulub Crater was officially official. 

An overlay of the massive Chicxulub Crater - image by University of Texas at Austin

When word about Chicxulub finally spread, scientific scrutiny revealed some incredible information.

The crater was even larger than Glen Penfield imagined. The 110-mile “bullseye” turned out just to be the inner wall. The outer wall actually features a 190-mile diameter. The blow required to create such a hole is estimated to be 4.5 million times stronger than the atomic bomb dropped on Hiroshima during World War II. The asteroid required to unleash that much damage was 6 miles across and taller than Mt. Everest.

Some of the details that scientists have modeled in regards to the collision are astounding to the point of being nearly unbelievable. The rock would have smashed Earth at a speed of approximately 19 miles a second. The impact would have caused winds in excess of 620 miles per hour. Megatsunamis rippled from the zone, some as high as 330 feet. One simulation stipulated that waves near the bullseye would have reached one mile in height. Of course, tsunamis don’t just happen on the surface. The waves from the impact raked the ocean floor itself, leaving the largest ripples ever documented on the seafloor near Louisiana. The entire bowl of the Gulf of Mexico felt the brunt, from Texas to Haiti and beyond. Sediments from the impact area have since been discovered nearly 4,000 miles away. 

As terrifying as these “local” events may seem, they paled compared to the global effects. Up to 25 trillion metric tons of earthly material rocketed upward. The blast was so mighty that some of this ejecta escaped the planet’s orbit. Parts of our planet are now floating throughout the solar system due to the Chicxulub asteroid. The material that did not escape Earth, of course, fell again. As superheated, incandescent death rocks. The surface of the planet caught fire; some estimates believe 70% of the forests were incinerated. Living beings in most of North and Central America would have been pulverized nearly instantly. The climate changed instantaneously. Dust filled the atmosphere, blocking sunlight and lowering temperatures drastically. Rain still managed to fall from the new clouds, but it was no longer water but acid. The food chain disintegrated.

Dust covered the entirety of the planet for a decade. Sunlight did not hit the surface for a decade. Most living things did not have a chance to survive. The biggest things had no chance. Large dinosaurs, long regents of the dry land, disappeared from Earth.

Though we cannot currently travel through time to see for certain if the asteroid that created the Chicxulub crater eradicated the dinosaurs, nearly all scientists today believe the evidence overwhelmingly suggests the concept is correct. Still, a few holdouts to the theory continue to cite a lack of fossil records. We see dinosaurs in the rock before the extinction event and we see other organisms in the rock after the extinction event. If so many creatures perished at the same time, why is there such a dearth in the rocks at the time of the event?

Of course, in many places, organic bodies were incinerated and could not fossilize. Perhaps the chaotic, violent shift in the planet simply did not allow for the proper preservation of living matter. Even if this scenario were true, one might expect a few examples of dinosaur fossils to surface in the timeframe of the Chicxulub asteroid.

2022 has provided, perhaps, the final piece of evidence to any remaining naysayers!

At a site in North Dakota, paleontologists have unearthed fossils they claim displays something amazing. Not only were the specimens killed in the ballpark of the extinction event, but they may have died on the exact day of the asteroid impact! 

In addition to dinosaurs at the site, called Tanis, scientists discovered fish with particles in their gills and a turtle impaled by a wooden stake. The particles are spheres of molten rock that they chemically linked to Mexico and radiometrically dated to the time of the strike. The researchers also believe they found shards of the asteroid!  Particles captured by tree resin at the site also show markers of extraterrestrial origin.

The claims are certainly extraordinary. As Carl Sagan always said, extraordinary claims require extraordinary evidence. The team in Tanis has worked for over three years to uncover as much evidence as possible. To pinpoint a specific date over 60 million years in the past almost seems impossible. However, the geologic evidence that a major extinction event would produce would certainly be unique. We might not know what the exact date of the impact was, but we may be able to piece together scientifically that these organisms died on whatever date it occurred.

The British Broadcasting Corporation spent the past three years overseeing the work in Tanis. In just a few days’ time, on 15 April, they will unveil a documentary in which Sir David Attenborough reviews the evidence. Obviously, the matter will not be solved, but these discoveries point to some wonderful conclusions in the mystery of the dinosaur extinction!

BONUS FACT: One of my favorite trivia tidbits involves Cleopatra and it never ceases to blow up my brain. The last active Pharoah of Ancient Egypt lived closer to 2022 than she did to the building of the pyramids in Giza. It’s often stated that she lived closer to McDonald’s than she did to the pyramids.

Another crazy timeline fact relates to today’s extinction topic. We tend to think of dinosaurs as a monolithic occurrence, but they lived during three different geological periods: the Triassic, Jurassic, and Cretaceous. These periods were mind-numbingly long. Tyrannosaurus Rex perished thanks to the Chicxulub asteroid at the end of the Cretaceous period. Thus, T. Rex lived about 66 million years from the time of humans. Stegosaurus had been extinct for 80-90 million years when T. Rex roamed the earth. So, the apex predator of Cretaceous Park lived closer to us than to his brethren in Jurassic Park!

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