It was the moment that reshaped our planet. One fateful day 66 million years ago, an asteroid
the size of a city came burning through the skies at 40 times the speed of sound before
crashing into the Yucatan peninsula. There, it exploded with the force of seven
billion Hiroshima bombs, liquifying the rock below it, and blasting a crater some 180km
wide. The sound of the impact was heard around the
world. In the minutes after, plumes of rock enveloped
the Earth in suffocating dust. Wildfires broke out across multiple continents. When the dust finally settled, it was onto
a planet that had lost 75 percent of its lifeforms. Today, the remnants of this long ago impact
are all but invisible, buried beneath thousands of meters of limestone. Yet, the crater still remains, half hidden
beneath the rainforests of the Yucatan, radiating out from the small town that gives it its
name: Chicxulub. But what stories lie behind the Chicxulub
crater? What would it have felt like to be living
on Earth at the moment the world ended? Today, Geographics is winding the clock back
tens of millions of years to witness one of the most important days in history: the day
the dinosaurs died. The Lost World
If you were to travel to the Yucatan rainforest today and stand within the confines of the
Chicxulub crater, you’d see a world that hasn’t changed for centuries. But no matter how deep you ventured into that
rainforest, no matter how far you got from human contact, you’d never find a world
as pristine as the one that existed here in the last days of the dinosaurs. At the time of the Chicxulub impact, the planet
was in the Late Cretaceous period. Following on from its more-famous sibling
the Jurassic, the Cretaceous was basically the Jim Belushi of geological eras - far-less
beloved, but far-longer lasting than its older brother. And we mean long. When the Cretaceous began 145 million years
ago, the supercontinent of Pangea was still just about holding together. By the time it ended in an apocalyptic blast
nearly 80 million years later, Pangea had broken up into landmasses pretty close to
what we have today. The wildlife had changed, too. To return to one of our favorite ways of measuring
time: you today are closer in time to the last T-Rex than that T-Rex was to the Jurassic
era’s stegosauruses. But were you to jump in a time machine and
travel back to the days of that last T-Rex, what would you see? Y’know, aside from the inside of a T-Rex’s
stomach? Well, the first thing you might notice is
how hot this lost world was. At the 45th parallel - roughly where the US-Canada
border is today - the climate would’ve been subtropical. Even the poles wouldn’t have been cool enough
to sustain year-round ice. The second thing you might’ve noticed was
how different it all seemed. At the end of the Cretaceous, early forms
of grass were only just starting to appear. Most modern trees were non existent. Ferns covered the land - not that there was
much land for them to cover: the sea levels were about 200m higher than they are today. The result? A planet that was only 18% land, compared
to 28% today. Even inland, vast shallow seas dominated huge
swathes of the world. But you probably wouldn’t be paying much
attention to any of this. Because the third thing you’d notice would
be all the seriously huge dinosaurs! In the southern hemisphere, sauropods like
the Dreadnoughtus roamed the plains. Clocking in at 26m long and weighing 60 tons
it was the largest land animal to have ever lived, a creature that would’ve made elephants
look like mice. In the sky above, Quetzalcoatlus soared - a
pterosaur that stood taller than a giraffe, and had an incredible 13m wingspan. Then there were the smaller, but still pretty
damn-big creatures. Across the northern hemisphere, vast herds
of Triceratops feasted on ground plants. T-Rex scavenged alongside them. In short, it was an incredible world, one
we can only imagine. And yet… in some ways, this lost world would’ve
been very familiar. By this point in history, flowering plants
had finally appeared. On the planet’s many warm shores, frogs,
turtles, and crocodiles all lived; while modern sharks swam in the oceans, passing over coral
reefs. Most-familiar of all, though, would’ve been
the mammals. While still small, these guys were now numerous
enough to leap right in to any handy gaps an asteroid impact might leave at the top
of the foodchain. In short, the Late Cretaceous was a boom time
for ecology, with a wonderful, dizzying array of creatures rubbing shoulders. But, as we all know, this Eden was doomed. Dinosaurs may have been around for 170 million
years - a period of time so long that there’s no point even trying to comprehend it - but
their end was already approaching at supersonic speeds. For better or for worse, this world’s time
was nearly up. The Day of Armageddon
In the course of Earth’s history, there have been five - or possibly six - major extinction
events. But none were so literally explosive as the
one that wiped out the dinosaurs. The day of impact likely dawned just like
any other day. There were no portents. No warnings. Just the sun rising as it had every day for
millions of years. Well, we assume so, anyway. Obviously with an event this far back, we
have no way of knowing if the asteroid hit in the morning, the afternoon, or the dead
of night. In fact, we don’t know a lot about this
day in general. This video is just using the most likely theories
based on current research. But adding endless caveats to our narrative
would get super boring, so let’s all just agree to allow us some poetic license. When the doomsday clock finally hit zero on
the Cretaceous era, it would’ve been shockingly sudden. You’ve probably seen footage of the Chelyabinsk
meteor that exploded over Russia in 2013, turning the sky a brilliant white. Against the Chicxulub asteroid, that blast
would’ve seemed like a firecracker against a hydrogen bomb. While the Chelyabinsk meteor was 18m across,
the one that hit Chicxulub was nearly 10km wide. When it smashed into the Yucatan at 40 times
the speed of sound, it was like hitting the Earth with a planet-scale bullet. In 1961, the Soviet Union tested the biggest
bomb ever deployed: the Tsar Bomba. It was the equivalent of setting off 3,800
Hiroshima’s simultaneously. Chicxulub was like 2 million of those Tsar
Bombas detonating all at once. The ground in the Yucatan was vaporized in
a split second. Rocks from far below the crust were hurled
high into the air - so high that a vast plume of dust was raised into the atmosphere. In the following seconds, an air blast shot
across Mexico and Central America, flattening forests for thousands of kilometers. Up to 1,400km away the heat pulse sent temperatures
soaring, igniting anything that could burn. Scientists who’ve studied the impact claim
the whole of modern Mexico was more-or-less instantly reduced to a sea of flames. If this was happening today, hundreds of millions
of people would already be dead. And things were about to get even worse. As the forests burned, gigantic tsunamis swept
across the Gulf of Mexico - up to 300m high - tearing up the seafloor and annihilating
coastlines. Magnitude 10 earthquakes tore the Americas
to pieces. As far south as Argentina, the shock of the
impact triggered landslides and volcanic eruptions. It’s almost inconceivable that anything
in the immediate area survived this Biblical-style apocalypse. But, if it did, it wouldn’t survive what
came next. Remember all those rocks from below the crust
that the impact launched into the air? Well, gravity was finally doing its thing. As the earth shook, the landscape burned,
and the tsunamis swirled, chunks of rock the size of skyscrapers fell back to Earth, burying
everything within several hundred km of the blast beneath flaming rubble. By this point, maybe a dozen minutes had passed
since the asteroid came streaking out of the sky. Before three quarters of an hour had passed,
things would go from “horrifying” to “literally the end of the world.” Armageddon
From space, the Chicxulub impact would’ve looked like a gigantic, angry flash, followed
by a period of eerie calm. As the minutes ticked by, that eerie calm
would’ve been displaced by the sight of a cloud of vaporized rock slowly pouring into
the atmosphere, embracing the world in dark fog. Inside that fog, tiny particles called spherules
were forming, made from the molten rock and glass created by the catastrophe. Only a few millimeters across, these spherules
would’ve looked harmless. Even strangely beautiful. But that would’ve been only a fleeting impression. After 40 minutes had passed, the spherules
now surrounded the planet. It was at this point that they began to fall
back to Earth. As University of Colorado geologist Doug Robertson
explained to Smithsonian: “The kinetic energy carried by these spherules
is colossal, about 20 million megatons total or about the energy of a one megaton hydrogen
bomb at six kilometer intervals around the planet.” When the spherules fell, they superheated
the atmosphere. In some places, the upper atmosphere would’ve
become so hot that the ground below burst into flames. The end result would’ve been uncontrollable
wildfires breaking out across the globe, as the spherules burned in the sky like falling
stars. For several hours intense heat swept the planet’s
surface, turning lakes to steam, cooking alive any animal unlucky enough to be out on the
plain. The only survivors in most places would’ve
been those that were underground or underwater. But even then it would’ve been dicey. Even as the heat roasted the Earth, tsunamis
were still sweeping the globe, swamping burning forests and dragging the burnt carcasses of
trees back out into the sea. After the spherules finally stopped falling,
the soot from the millions of fires would’ve combined with the dust thrown up by impact,
rising into the atmosphere and completely shrouding the world. Speaking of that dust; it’s extremely unfortunate
that the asteroid hit where it did. There have been over five bigger impacts than
Chicxulub in Earth’s history. One of them even landed after dinosaurs had
evolved, and didn’t cause anything like a mass extinction event. But that’s what makes Chicxulub special. It hit the Yucatan, an area with layers of
many volatile rocks. As National Geographic once put it: “There
are relatively rare areas of the planet that you can drop a 12-kilometer asteroid on and
get the same level of atmospheric change.” Chicxulub just happened to be one of them. As the first survivors of the cataclysm began
emerging from whatever rocks they were hiding under, it was into a world that had changed
beyond all recognition. The land was now gray, coated with a thick
layer of ash. Forests were gone, coastlines devastated. High above, soot and dust would’ve swirled
across the skies, reducing the sun to a feeble, almost invisible point. These surviving animals couldn’t possibly
have known it, but the devastation unleashed by Chicxulub had barely even begun. Had they been capable of abstract thought,
they would’ve soon realized that the dead creatures around them were the lucky ones. Aftermath
For the next year, the Earth was plunged into
an endless winter. With the upper atmosphere so clogged, zero
sunlight would’ve peeked through. It would’ve been cold, dark, and nasty;
like an ancient vision of the underworld. It would’ve also been exceptionally deadly. So, you might remember from biology class
what happens to plankton when it goes without sunlight. To paraphrase a famously-terrible movie line:
the same thing that happens to everything else. It dies. Horribly. While that sucked for the plankton, it also
sucked for everything that ate that plankton to survive. And everything that ate the things that ate
that plankton to survive. And everything that ate the things that ate
the things that ate… well, you get the idea. Across the ocean, the entire foodchain collapsed. On land, every single day became a hyper Darwinian
struggle for existence. We recently did a Geographics on Stalin’s
cannibal island of Nazinsky, where thousands of political prisoners were dumped in the
depths of winter without food or water and forced to murder and eat one another in order
to survive. That horrific experience lasted only a couple
of months. For anything alive after Chicxulub, it would’ve
been like being stuck on cannibal island for decades. Starvation would’ve been the default setting
of every living thing. Thirst, too. Acid rain fell from the burnt skies, poisoning
water supplies, turning former forests into the surface of the Moon. In the decades after Chicxulub, around 75%
of all species vanished. The lucky 25% of species that did pull through
were likely pushed to the very brink of extinction. It’s thought today that no land animal larger
than a raccoon made it through Chicxulub’s great filter. The only reason small mammals fared so well
is because they required less food, and bred faster. But even for mammals existence still became
an unending nightmare struggle. Yet, even in these dark times, life found
a way. At ground zero, it was long assumed that the
32km deep impact crater would’ve been completely sterile, a place nothing could survive. But today we know that even at Chicxulub itself,
cyanobacteria began creeping back within a couple of years, creating toxic algae blooms. As the sunlight began to return, the charred
forests were repopulated, too. First by ferns, and then by mosses and, eventually,
more complex plants. As the dinosaurs and their doomed brethren
died off, the mammals moved into the spaces left in the environment. And, slowly, they began to thrive. By the time 30,000 years had passed life was
stabilizing. Although it would take hundreds of thousands
of years for ecosystems to settle into their new grooves, eventually they would. In this brave new world at the dawning of
the Cenozoic era, those lucky mammals that had survived would go on to evolve. At long, long last, their descendants would
become humans. Recovering the Past
So that’s What happened, but what about the How? Not how did an asteroid strike the Earth - that’s
pretty self-explanatory - but how did we discover the Chicxulub impact? I mean, it’s not like there were dinosaurs
keeping diaries. The answer to that is almost as fascinating
as the impact itself - albeit “fascinating” in a way that involves far less mass death. It wasn’t until fairly recently that “what
killed the dinosaurs” became a question people thought worth answering. Part of this is to do with the fact that “dinosaurs”
as a concept have only existed since 1842. That was the year that parttime genius and
fulltime jerk Richard Owen realized all the fossils guys like William Buckland had been
digging up over the previous 20 years were clearly related. Owen is the guy who gave them the name “dinosaurs”. But even as these terrible lizards gripped
the 19th Century imagination, no-one gave much thought as to why they were no longer
around. It wasn’t until the turn of the century
that people looked at this by-now gigantic pile of ancient bones and started to wonder
“what happened?” And according to olde timey folk, what had
happened was utter insanity. At the saner end of the scale, you have George
Wieland’s 1925 hypothesis that the dinosaurs got so super into eating eggs that they devoured
all their own offspring. At the total looney tunes end, you have the
gloriously named Baron Franz Nopcsa von Felső-Szilvás declaring that the dinosaurs were killed off
by their lack of sex drive. But while it’s fun to discuss these old
theories, like the one that seriously claimed a whole bunch of very hungry caterpillars
ate all the vegetation thus making the dinos starve, we need to skip ahead in time a little
now, to the late 70s. Because this is when the existence of Chicxulub
itself finally became clear. In 1978, a geophysicist named Glen Penfield
was working for Mexico’s state oil company Pemex in the Yucatan. As part of his duties, Penfield was flown
out over the Gulf of Mexico with a magnetometer so he could scan for oil. Instead, he found something much stranger. Below the waves, Penfield could distinctly
trace the outlines of a perfect semicircle - the underwater remains of the impact crater. Unfortunately, Pemex refused him permission
to make his findings public - beyond the fact that there might be a big ol’ crater down
there. But soon others would independently begin
looking for impact sites. In 1980, Luis and Walter Alvarez discovered
a thin layer in the geological record marking the end of the Cretaceous across the entire
world. This layer was rich in iridium, an element
rare on Earth, but common on asteroids. That same year, the father son team declared
their theory that an asteroid had wiped out the dinosaurs. It wouldn’t be long before others were backing
up their findings. There was Carlos Byars, the Texan journalist
who was the first to link the Alvarez theory with Penfield’s little-known crater. There was Alan Hildebrand, who discovered
evidence of an mega impact 66 million years ago while working in Haiti, and summarized
the Alvarez asteroid must’ve hit the Caribbean. Then there was NASA scientist Adriana Ocampo,
who discovered that the distribution of cenotes in Yucatan - bright blue water holes the Maya
once used in their rituals - formed the second half of Penfield’s underwater crater. In the early 1990s, all of the threads came
together. It was announced that not only was the Alvarez
asteroid theory the best candidate for Earth’s fifth mass extinction, but that the site was
almost certainly centered on the town of Chicxulub in Mexico’s Yucatan. And, just like that, we finally discovered
how the dinosaurs had died out. Or did we? The Endless Controversy
Today, the Chicxulub theory is one of the most-accepted in all of science. Seriously, while researching this video, we
saw people saying it was as sure a bet as the theory of evolution. But we’d be neglecting our duties if we
didn’t point out that some super-qualified people still believe that we’ve got it wrong,
that an asteroid impact alone didn’t wipe out the dinosaurs. So what did? Well, according to these guys, it was volcanoes. Of the five mass extinction events in Earth’s
history - six if you accept the argument that the end-Guadalupian event should count - most
of them are suspected to have been caused by volcanoes. In fact, volcanoes are the leading culprits
in the Great Dying 252 million years ago, the worst mass extinction event in Earth’s
history, and one where up to 96 percent of all species were wiped out. Given supervolcanoes leading to climate change
might’ve wiped out life on Earth on a pretty regular basis, some started looking for evidence
they killed the dinos, too. In India, they may have found it. The Western Ghats are a mountain range in
the Indian south, formed when a huge series of volcanoes known as the Deccan Traps blew
their tops 66 million years ago. We know that they started erupting 400,000
years before Chicxulub, and that overall they sent 562,700 cubic km of material to the surface
- tens of thousands of times what Krakatoa unleashed. But as to whether they killed anything more
than a handful of unlucky dinos chilling out in India, doing some yoga and finding themselves…
well, that depends on who you ask. Supporters of the volcano theory contend that
the Deccan Traps had already unleashed so much greenhouse gas into the atmosphere when
Chicxulub hit that the Earth was already on life-support. So getting pummeled by an mega-asteroid was
just the final blow in two-punch extinction event. This is backed up by a recent study showing
a huge uptick in the amount of material the Deccan Traps were sending out in the 100,000
years before Chicxulub. On the other hand, supporters of the asteroid
theory counter that a separate study published the same year concluded that the Deccan Traps
only became properly active after Chicxulub; making them an apocalypse sideshow at best. Weirdly, these arguments get quite heated. Like, as hot as a spherule falling back to
Earth. Leading proponent of the volcano theory Gerta
Keller has claimed that “impacters” have tried to destroy her career and have her driven
out of academia for being anti-asteroid. And you thought your workplace was tough. Still, for now, the Chicxulub impact remains
our best guess for what happened to the dinosaurs. Maybe it’ll be proven wrong in a few years. Or maybe all this talk of volcanoes is just
a load of hot air. Today, the Chicxulub crater is all but invisible
to the human eye - buried under tropical rainforests, or simply lost beneath the waves. If you were to travel to the town the crater
is named after, you’d find nothing there to tell you that this is it. That here is the spot where the age of dinosaurs
ended, and the age of mammals began. Nothing to tell you that, without this one
event on a single peninsula so many millions of years ago, the dinosaurs might never have
vanished. Yet, sign or no sign, the impact of this invisible
crater cannot be overstated. In the months that Geographics has been running,
we’ve covered all sorts of locations, each important in their own way. Some have been important to a certain region
or certain time. Some have been important to entire eras. But none have been so important as the Chicxulub
crater. Without that long ago asteroid impact, none
of those other videos would’ve had anything to cover. The Pyramids, the lost Mayan cities, the microstates,
the prisons, the international borders… none would’ve existed. We’d have had no Mona Lisa, no Renaissance,
no Bible, no Shakespeare, no agriculture. There wouldn’t even be a we to know what
we were missing. There’d just be nothing. Nothing but a watery blue world on which the
human race had likely never evolved. If just one of a billion variables had shifted
even slightly, the Chicxulub impact could’ve been in the open ocean, or somewhere where
there was less volatile rock to choke the atmosphere, or it could’ve missed Earth
entirely. Imagine that. Imagine all the things that had to go horribly
wrong for the dinosaurs to wipe them out that fateful day. All the things that had to go horribly right
for us mammals to get a chance at ruling the Earth. If the history of all life on Earth is the
history of a string of remarkable coincidences, then this may be the most remarkable of them
all. Forget “the asteroid that killed the dinosaurs.” We today should think of this vast, ancient
crater as Chicxulub: the impact site that made humanity possible.
