Chicxulub crater might be the smoking gun for the dinosaurs' end of days
- Millions of years ago, a dramatic mass extinction wiped out the dinosaurs.
- Marking the transition between the Mesozoic and Cenozoic eras (which we are still in), it was one of the most significant events in Earth's history.
- The cause? Perhaps a giant asteroid hit Chixculub near modern-day Yucatan, Mexico.
Sixty-six million years ago, something from the very edge of our solar system completed its unlikely journey into the inner planets. Rather than passing by or Jupiter taking one on the chin, like so many end up, this one smashes into the Earth's surface, causing such devastation that it wiped out almost 2/3 of all life.
The impact site, near Chixculub in Mexico, triggered global fires, tsunamis, and a nuclear winter that likely extinguished many long-lived species, including the dinosaurs, in a short time.
But what was it? Where did it come from? And could we survive another today? Let's find out.
What is the Chicxulub crater?
Chicxulub is an impact crater in Mexico located partly onshore and partly offshore of the Yucatán Peninsula's coast. Its center is close to the town of Chicxulub, after which it was given its name. While this impact site is now famous, you can't really "see" it today as it is partially underwater.
It is thought to have been created more than 66 million years ago when an enormous asteroid with a diameter of around 6 miles (10 kilometers) collided with Earth. The crater's diameter and depth are believed to be 110 miles (180 kilometers) and 12 miles (20 kilometers), respectively.
The impactor was estimated to be roughly 6 miles across at the larger end of the scale of estimates. This is hard to visualize just how big that would be. But, to give you some idea of scale, it would be roughly thirty times as wide as the Empire State Building (measured from the base to the tip of its lightning rod at 1,454 feet or 443.2 meters).
It created the second-largest confirmed impact structure on Earth, and its peak ring is the only one that is still whole and easy for scientists to study.
At the time of the impact, the Earth's continents were also closer than they are today (and the Atlantic Ocean was smaller, for example). This may have made the impact possibly more devastating than it may have otherwise been.
Geophysicists Antonio Camargo and Glen Penfield, searching for oil on the Yucatán Peninsula in the late 1970s, discovered the crater. At first, Penfield could not find proof that the geological structure was a crater and gave up looking.
Later, Penfield received samples from Alan R. Hildebrand in 1990, which showed that it was an impact feature. There are signs, such as shattered quartz and tektites in the area, that an impact made the crater.
The impact occurred during the Cretaceous-Paleogene transition (known as the K–Pg or K–T boundary). The Cretaceous-Paleogene extinction event, which killed off around 75 percent of all plant and animal species on Earth, including the ancestors all non-avian and non-crocodilian dinosaurs, is now thought to have been caused by the damage and climate change that followed.
How did Chicxulub affect the Earth?
The short answer is that it irrevocably changed the planet forever. Many animals and plants were wiped off the face of the Earth almost overnight, and the evolutionary history of our planet was violently changed.
There are two easy ways to examine how the environmental changes mentioned above affect the world.
One can first consider them as a function of time following the impact event. The immediate local and regional impacts happened, including a fireball of radiation, an airblast, and tsunamis. Fires caused by impacts, for example, could have continued for months. Even if the fires did not burn for very long, their aftereffect, like soot cooling, did.
Over time, soot in the air would have led to sulfate aerosols, nitric acid rain, and sulfuric acid rain. The sulfuric acid rain probably continued for 5 to 10 years before it stopped. There would have been decades, if not longer, of greenhouse warming. Some models predict that the greenhouse effect has been around for thousands of years.
Think about what would happen if the event occurred in a single area, like the Raton Basin in Colorado and New Mexico. This is another way to think of the effects on everyone.
The second is the broader impact on the Earth.
After the impact, the temperatures likely went up and down like a yo-yo. There would have been several temperature jumps as debris from the Chicxulub crater showered into the atmosphere. It's possible that the high temperatures burned the grass. Temperatures would then have plunged below those before impact once the atmosphere was covered with dust, soot, and aerosols, blocking the sunlight. It was going to be chilly. Then, once greenhouse gases started to affect the climate over far longer durations, temperatures would again have increased dramatically.
But that is the longer-term impact. Perhaps more interesting is what is thought to have happened minutes, hours, and days after that cataclysmic day.
What happened the day the Chixculub crater formed?
And that is where one group of scientists made some exciting discoveries in 2019.
Sean Gulick, a geologist at the University of Texas at Austin, and several other academics have used a core sample from 2016 to help us learn more about the Cretaceous-Paleogene extinction. According to the geologic time scale, this portion is meant to include the first day after the asteroid impact, making it the first day of the Cenozoic since the Cretaceous ended at the time of the impact, according to Gulick.
The research team's paper, "The First Day of the Cenozoic," was released in the Proceedings of the National Academy of Sciences.
According to the study, when an asteroid the size of the Chicxulub impactor, which is thought to have been over 6 miles (10 km) wide, collides with the planet, the material is pulled up from underneath the surface and thrown into the air, resulting in the collapse of a circular mountain range inside the crater.
You can see this process in miniature if you drop something into a body of water. Watching some slow-motion footage of the reaction on the water's surface gives you a good idea of the processes that occur when a large bolide strikes the surface of a planet.
Of course, with material like rock, the surface doesn't completely recover to a flat plane, like in water. The structure that formed is preserved.
Such catastrophic upheaval sets off a chain reaction of natural catastrophes that likely sent tsunamis sweeping across the oceans and hurling colossal amounts of debris into the skies.
The geologic record of the core sample is several hundred feet deep. Over 400 feet (122 meters) of melt rock deposited the day after the impact can be found beneath a thin ring of overlying material.
“This isn’t the first drill core from Chicxulub,” University of New Mexico geologist James Witts told the Smithsonian Museum in an interview, “but because of its position on the peak ring, which is essentially a range of mountains created in the moments after the impact event, it provides a unique picture of the sort of dynamic geological processes that operated over short timescales.”
Since the magnitude of such an event has never occurred in human history, the rock record is crucial to figuring out the specifics.
Gulick and colleagues discovered that the underlying rock at the impact site disintegrated and formed a crater with a peak ring within minutes of the asteroid collision. Over 70 feet (21 meters) of additional rock melted in the blast's heat and covered the ring.
And that was only the beginning.
Did Chicxulub create a tsunami?
In the minutes and hours that followed, surges of water surging back into the crater laid down more than 260 more feet (79 meters) of melted stone on top of the already collected rubble. A tsunami then struck.
The impactor's speed has been calculated to be 7.5 miles per second (12 km per second), perhaps more. This would have given the impactor's kinetic energy somewhere in the region of 100,000 gigatonnes of TNT. For reference, that dwarfs anything human beings have ever been able to produce, even the planet's total combined nuclear weapon yield.
This was so much power that near the blast's center, the impact produced winds exceeding 620 mph (1,000 kph) and briefly created a hollow that was 62 miles (100 km) wide and 19 miles (30 km) deep until it eventually collapsed.
Within the first 24 hours of the strike, the wave reflected toward the crater following the original impact, adding another distinct layer of rock, including gravel, sand, and charcoal deposits.
The collision started forest fires inland that was eventually put out by tsunami waves closer to the shore. The charred wood debris washed into the ocean, and some gathered in the crater.
And that's just locally. The impact had a massive influence on life far from the site too.
According to Gulick, the heat pulse would have caused temperatures to increase more than 900 miles (274 km) distant, and "at greater distances, the ejecta might also have ignited fires by frictional heating as it rained down in the atmosphere," he adds.
Sulfur was abundant in the rocks that the asteroid smashed. When it impacted them, it ejected and evaporated the sulfur, which mixed with water vapor to produce what Gulick refers to as an aerosol sulfate haze. Geologists had previously observed and analyzed this phenomenon, but the latest findings support the part this atmospheric disruption had in the subsequent extinction.
“Our results support this scenario where first you burned parts of the continents, and then you had global dimming of the sun and plummeting temperatures for years to follow,” Gulick told the Smithsonian. These events account for the loss of 75 percent of known species at the end of the Cretaceous. Had the impact occurred elsewhere or in a place of deeper ocean water, the extinction may have happened differently or not at all.
The Chicxulub crater cores show the extent of the planet's destruction, but Witts predicts some disagreement over when these events occurred.
“The complication with relating individual deposits in the core to specific types of events is that clearly, the crater wasn’t a static environment after formation,” Witts explained to the Smithsonian.
This means that over 66 million years, earthquakes, waves, and other occurrences changed the rock record. Even so, cores like the one extracted from the peak ring demonstrate that we may examine short-term events in the rock record in detail, down to the level of minutes, hours, and days.
For a process that usually takes tens of thousands or millions of years of plodding and steady progress, insights into sudden violent changes to the Earth's rock records are fascinating for geologists. For anything alive at the time, this must have been a very, very distressing time (if they survived for long enough to experience it, of course).
Did the Chicxulub crater kill the dinosaurs?
In short, we are not sure. While it wouldn't have impacted them severely, dinosaurs may already have been on the decline well before the cataclysm.
To borrow a phrase, it may have been simply the coup de grâce that finally ended them.
As the British Natural History Museum explains, "The blame can't solely rest on the asteroid. Before the [impact], Earth was experiencing a period of climate change. This was making things harder for life on our planet."
Despite being unrelated to the asteroid impact, significant volcanic activity in central India caused its issues. Called "The Deccan Traps," this was an enormous outpouring of lava that would have dramatically impacted the Earth's climate well before the impact.
Lasting for at least two million years before the asteroid visited Earth, this volcanic activity would have released vast volumes of gases into the atmosphere that would have significantly affected the climate.
Longer-term changes were also going on around the time.
The continents were moving about and breaking apart, which led to the creation of larger oceans, which altered global patterns of weather and climate. Climate change and vegetation were both significantly impacted by this.
Whether severe climate change or an asteroid impact, many creatures and plants became extinct, ever to return.
Ammonites were just one animal species that perished 66 million years ago during the Cretaceous-Palaeogene extinction catastrophe. They had been around for over 140 million years, give or take.
As for the dinosaurs, many dinosaur species already showed a decline before the asteroid impact. However, very few, if any, non-avian dinosaur species managed to limp after the event.
Only the ancestors of modern birds and crocodiles appear to have the "right stuff" to have survived in the post-apocalyptic world in the years after the K-T boundary.
Was the Chicxulub crater formed by an asteroid or a comet?
So, what kind of space object hit Earth on that fateful day 66 million years ago? Was it a comet or an asteroid? Can we ever know?
The scientific consensus hasn't changed much since the first proposal of a bolide impact in the 1980s; it was most likely an asteroid. Evidence for this is the relatively high concentrations of an element called iridium that contaminated most sediments formed at the time of the impact.
What's more, this iridium-rich layer can be seen all over the world.
Rare on Earth, iridium, it turns out, is quite common in asteroids! But not all scientists agree; some have suggested the impactor was more likely a comet!
For instance, Harvard astrophysicists Amir Siraj and Avi Loeb suggested that comets best match the geochemical evidence, which shows that the impactor had a carbonaceous chondrite composition, in a paper published in February 2021. Carbonaceous chondrites are a relatively uncommon kind of black, primordial meteorite with a high carbon content and minerals that have been affected by water.
Siraj and Loeb also determined that roughly one-fifth of all long-period comets—icy wanderers that take longer than 200 years to complete one orbit—split into several pieces when they approach the Sun.
"This population could increase the impact rate of long-period comets capable of producing Chicxulub impact events by order of magnitude," Siraj and Loeb wrote in the study, published in the journal Scientific Reports.
"This new rate would be consistent with the age of the Chicxulub impact crater, thereby providing a satisfactory explanation for the origin of the impactor," they added.
Interesting, but other experts disagree.
For example, researchers Steve Desch and colleagues from Arizona State University noted that comets only correspond with a particular class of carbonaceous chondrite known as CI, which is not the fingerprint the impactor left behind.
"Careful consideration of the geochemical evidence strongly favors a CM or CR carbonaceous chondrite and rules out a cometary impactor," Desch et al. wrote in their paper, which was published in June 2021 in the journal Astronomy & Geophysics.
In response to that remark, Siraj and Loeb wrote a piece that adds to the ongoing discussion that lasted for 40 years and may go on for decades more. Nevertheless, Siraj and Loeb represent the minority in this situation. According to Desch and his team, "The broad consensus is in favor of an asteroid impactor."
Chicxulub Crater's measurements, which are approximately 90 miles across by 12 miles (20 km) deep, give us a general estimate of the impactor's size.
Siraj and Loeb, for instance, estimated that the approaching object was probably around 4.3 miles (7 km) wide. But this is assuming that the impactor was a chunk of a long-period comet. The more eagle-eyed among you will notice that this is a little smaller than most quoted figures.
But this can be explained by a straightforward fact; comets tend to travel much faster than asteroids and, therefore, have relatively more momentum. To borrow a phrase, they can give you more bang for your buck.
To rip a Chicxulub-sized hole in the Earth, a larger asteroid from the main belt between Mars and Jupiter must have moved more slowly than a smaller long-period comet. Whatever it was, the space object responsible was huge and had enough oomph to cause one of the worst extinction events in Earth's history.
Where did the Chicxulub asteroid come from?
The impact and its aftermath are well-known but assuming the impactor was an asteroid, where did it come from?
Unless we could build a time machine and travel back to find out, scientists today are left with the need to make some educated guesses. But the main asteroid belt of our solar system might be a good bet.
According to a 2007 study, the Dino-annihilator asteroid may have resulted from a freak collision in the belt, setting off a chain of events that ultimately spelled disaster for life on Earth at the time.
According to the study, a massive collision in the innermost region of the main asteroid belt about 160 million years ago broke apart a 106-mile-wide (170 km) space rock dubbed Baptistina.
"Fragments produced by the collision were slowly delivered by dynamical processes to orbits where they could strike the terrestrial planets," the researchers wrote in the 2007 study, which was published in the journal Nature.
"We find that this asteroid shower is the most likely source (>90 percent probability) of the Chicxulub impactor that produced the Cretaceous-Tertiary (K-T) mass extinction event 65 [million years] ago," the study adds.
However, observations by NASA's Wide-field Infrared Survey Explorer spacecraft in 2011 showed that the in-space collision was probably only around 80 million years ago, effectively disproving the "Baptistina" idea.
According to the researchers, the freshly formed fragments didn't have enough time to migrate into a position from where one of them could be gravitationally propelled onto an Earth-crossing trajectory. However, the parent body of the dinosaur-killing asteroid is still a mystery; its origin is unknown.
But, a 2021 study may have narrowed things down for us a bit.
In their study, Southwest Research Institute (SwRI) researchers David Nesvorn, Bottke, and Simone Marchi conducted computer simulations to better understand the asteroid population and significant impacts, such as the one that triggered the K-T mass extinction.
They concluded that the asteroid responsible for the dinosaur extinction once lived in the main belt, most likely in its outer regions.
Nesvorn and his team also estimated that the black carbonaceous asteroids, which make up around half of all objects that strike the Earth, are wider than 3 miles (5 km). They also calculated the likelihood of an impactor at least 6 miles wide striking our planet once every 250 million to 500 million years.
Hopefully, their calculations are at least in the ballpark. If so, perhaps, there won't be another one coming our way for a while.
What survived the Chixculub impact?
The K-Pg extinction significantly impacted (pardon the pun) the evolution of life on Earth. Due to the replacement of prominent Cretaceous groups by different creatures, the Paleogene Period saw significant species diversification.
The eradication of dinosaurs in favor of mammals is the most striking example. Mammals quickly evolved during the K-T extinction to fill the voids left by the dinosaurs.
Other groups have likewise significantly varied. According to DNA sequencing and fossil dating, numerous bird species (the Neoaves group in particular) appeared to have spread out after the K-Pg boundary.
They included enormous, flightless organisms like the herbivorous Gastornis and Dromornithidae and the carnivorous Phorusrhacidae
It's possible that contemporary subspecies like iguanas, monitor lizards, and boas evolved due to the demise of Cretaceous snakes and lizards.
Giant boidae and massive madtsoiid snakes first appeared on land, and giant sea snakes later developed in the waters at this time. Teleost fish rapidly underwent diversification, occupying the extinction-related voids.
Billfish, tunas, eels, and flatfish are just a few of the groups that have been found in the Paleocene and Eocene eras. Paleogene insect communities have also undergone significant modifications. In the Cretaceous, there were numerous ant species, but in the Eocene, ants were more numerous and diverse and had larger nests.
Additionally, butterflies evolved at this time, possibly to occupy niches left by the leaf-eating insects that became extinct. Termitidae, the sophisticated mound-builders, also seems to have gained significance.
Plants were less impacted than animals during the Cretaceous extinction event because their seeds and pollen can endure harsh conditions for extended periods. Following the demise of the dinosaurs, flowering plants took over, continuing a process that began during the Cretaceous and is still going strong now. However, anything weighing more than about 55 pounds (25 kg) and living on land appears to have become extinct.
As for the dinosaurs, those that weren't birds all perished, but dinosaurs that were the ancestors of birds did survive (obviously).
Dinosaurs are the largest land animals ever to have existed. Whales are the only animals to have surpassed them in size in the millions of years since their demise.
Could the dinosaurs have survived the impact?
According to some studies, the fate of life on Earth would have been quite different if the impact had taken place on an other part of the planet. If, for example, the asteroid had landed in deeper water, less rock would have vaporized and risen to block the Sun's light and warmth.
As a result, the impact would likely have been destructive but not as catastrophic as it was.
If this had happened, we might even have seen some dinosaurs (other than birds) around today if the dinosaurs' reign hadn't been abruptly ended by an asteroid.
Triceratops was one of the last non-avian dinosaurs to become extinct; therefore, if the asteroid hadn't hit Earth, some believe there is a chance that some descendants of the triceratops might still be alive today. This dinosaur, almost uniquely, appears to have been able to limp on for a few million years after the impact but, ultimately, couldn't make it to the present day.
We may very well have seen a world of large dinosaurs and big mammals coexisting in the modern day. Who knows, without the impact, or with an impact in a different location, Earth today may have resembled the fantasy worlds of films like "Jurassic Park" or computer games like the "Monster Hunter" series.
But whether our early ancestors would have been able to survive in such a world is very much up for speculation.
However, as we've already pointed out, environmental changes took a massive toll on the dinosaurs well before the impact. It may be the case that even if the asteroid hit deeper water, the fate of the dinosaurs was already a foregone conclusion.
Unable to compete in a rapidly changing world, they would likely have eventually gone extinct with or without the asteroid impact. However, we can never know for sure.
Could something like Chixculub happen again, and could we survive?
With the sheer size and scale of the devastation wrought by the Chixculub impactor, you might wonder if it could ever happen again. Well, the answer is.... perhaps.
A list of objects that theoretically could strike Earth in the next 1,000 years currently has roughly 1,200 asteroids on it, all of which are smaller than one kilometer. A Chicxulub-sized asteroid hitting Earth is unlikely but possible. Impactors of this size appear to strike the Earth once every 100 to 200 million years or so.
Great news! Sort of, but should we survive for another 40 million years or so to see the next one, or if one popped out of the blue tomorrow, how would we fair?
According to Forbes, a study published by physicists Philip Lubin and Alexander N. Cohen from the University of California, Santa Barbara, found that there was a possibility that humanity would survive a similar hit today.
Dealing with such a potential threat can be accomplished in three ways.
The first and best action is to stop the impact by destroying the asteroid or altering its course in advance. Scientists are already looking for asteroids that could collide with Earth and debating potential defense measures. But blasting them with bombs or planting them Armaggedon-style might be a little out of our current ability.
Parts of the asteroid may be destroyed by nuclear bombs, breaking it into smaller fragments that would either completely miss Earth or burn up in the atmosphere. Rockets and nuclear weapons are already developed enough to successfully intercept and destroy asteroids around 2/3 of a mile (one kilometer) in size.
This approach won't work with larger asteroids like Chicxulub because the yield required to melt or fragment the entire mass is greater than the total number of nuclear weapons. If the asteroid is caught in time, it might be deflected from its crash course by a series of bursts from conventional atom bombs.
As NASA's recent DART mission showed, if the asteroid is smaller, it may be possible to deflect it by crashing a spacecraft onto it.
In fact, according to most experts, asteroids larger than 25 miles (40 kilometers) in diameter are essentially unstoppable with existing technology.
If the impact cannot be avoided, the second plan calls for building massive subterranean bunkers to withstand the blast and its aftermath. The authors conclude that bunkers could also preserve humanity by arguing that numerous creatures that live below or in the deep sea have survived the catastrophic extinction that occurred 66 million years ago.
Underground facilities would shield humans from the impact's immediate impacts, such as the blast and fires, and it's aftereffects, such as an impact winter. This is, after all, probably what some of our mammalian ancestors did during the Chixculub event.
The final tactic is to ignore the issue and accept our fate. But, knowing our species, this would not be likely. But, of course, we can never know until such a day arrives.
And that is your lot for today.
That day 66 million years ago changed the history of life on our planet forever. Whether it was the ultimate cause or just the final killing blow, the undisputed rulers of the Earth were toppled from their throne, opening up a power vacuum of sorts for other creatures to fill.
Thankfully for us today, our early ancestors did very well in the aftermath, paving the way for our species' evolution tens of millions of years in the future.
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