Chicxulub: The End of the Age of Reptiles

by Sam Atkins

NOTE: Tap or hover over images for captions and credits.

Image credit: Gerhard Boeggemann

66 million years ago. Late Cretaceous Period. Central America.

A family of Coahuilasaurs, a species of duck-billed hadrosaurs, wade through a muggy, fly-ridden valley. The unforgiving sun is crawling down toward the mountain range to the west. The mother and her three young calves pant in anticipation for a reprieve from the sweltering heat. They plod through a well-travelled field of ferns clenching mouthfuls of green fronds in their rows of teeth and ripping them away. As they grind up the foliage, they dig their toes comfortably into the damp soil. The mother’s head is turned by the guttural drone of a distant carnivore echoing across the field and she nudges her young to pick up the pace. Just as they cross a scattering of hearty cycad trees and climb up the grassy mound beyond, a winding river enters their sights. The young calves bleat with excitement for their thirst to be quenched.

The vibrant sounds of the valley — the chirps of insects, the rustle of ferns — fade into an eerie silence. The mother’s head is on a swivel, wondering what is happening. The silence gradually gives way to a mysterious rumbling… but not from below. Suddenly, the sky explodes in a cascade of light. The mother squints, arches her head and leans back onto her hind legs. It’s as if another more powerful sun formed in the sky. The pink and purple of twilight turns to black while the whole valley below is bathed in a heavenly glow. A flock of pterosaurs screeches overhead, their wings beating furiously as they flee. The Coahuilasaurs are engulfed by an intense heat. She instinctively trots circles around her children, hoping to shield them from danger. The closer the object gets to the horizon, the more blinding and searing its light becomes until the mother and her calves are enveloped in it. In the following moments, the trajectory of life on Earth is irrevocably changed forever.

Piecing Together The Past

Image credit: Rob Glover

Humans have been recovering dinosaur fossils all around the world since the early-19th century. Whenever a dinosaur would die millions of years ago, their bodies would sometimes become quickly buried in sediment such as mud, sand or volcanic ash. This would act as a protective barrier from decay and scavengers. As their entombed remains slowly decomposed, minerals in the surrounding sediment would seep in to replace the organic material in their bones. This process, which takes millions of years, would preserve evidence of the creature in the form of fossils for paleontologists to eventually uncover.

The idea that dinosaurs were killed in a mass extinction event, as opposed to gradual evolutionary change, developed around the late-19th century. Scientists observed a point in the geological strata that shows a very clear and distinct change in the fossil record. Today, this is called the K-Pg boundary (Cretaceous-Paleogene boundary). Below this boundary, fossils of dinosaurs and a diverse array of other species are prevalent. Above this boundary, there is a dramatic reduction in diversity, particularly of large reptiles. Even more compelling is that this boundary has been found consistently around different parts of the world such as North America, Europe and Asia. Many competing hypotheses sprung up to explain the sudden disappearance. Extreme volcanic activity, climate change, the magnetic reversal of the poles, sea-level changes and even a nearby supernova were among the broad range of proposals. This mystery would puzzle scientists for several decades.

Rock sample from Wyoming showing the clay layer deposited by the asteroid. Image credit: Eurico Zimbres

In 1980, an American geology team consisting of Walter Alvarez, his father, Nobel Prize-winning physicist Luis Alvarez, and a grad student named Alan Hildebrand, published a paper detailing their theory of what caused the mass extinction event. They reported that a thin layer of clay at the K-Pg boundary contained significant levels of iridium, a dense silvery-white metal belonging to the platinum group. It is one of the rarest elements in Earth’s crust, often needing to be extracted from nickel and copper ores. However, at the K-Pg boundary it was found in quantities hundreds of times the normal amount. While rare on this planet, there is a place where we do find it in abundance: meteoric iron. The significant presence of iridium throughout this layer points to an asteroid impact. There was only one problem. An asteroid big enough to wipe out three quarters of the species on Earth would have left a pretty large crater. So where was it?

Image credit: Google Earth

Image credit: NASA/JPL-Caltech

In 1978, just a few years prior to the publishing of the Alvarez hypothesis, two geophysicists named Glen Penfield and Antonio Camargo were working for the state-owned oil company Pemex, scouring the Yucatán Peninsula in Mexico for petroleum. Aerial magnetic survey maps revealed a distinct and expansive circular structure, about a kilometer underground and 180 km in diameter, straddling the Gulf of Mexico. They managed to get their hands on an old gravity anomaly map of the peninsula from Pemex archives. These maps are created using data from gravimeters that detect minute variations in the density of Earth materials. This map showed the same structure as their magnetic survey.

Penfield and Camargo believed it to be an impact crater but Pemex dismissed their hypothesis in favor of volcanic activity as an explanation. However, they did allow them to present their findings at the 1981 Society of Exploration Geophysics conference in Los Angeles. Unfortunately, nobody who was familiar with the iridium-rich layer found by the Alvarez team was in attendance. Penfield knew that Pemex had drilled exploratory wells into a thick layer of andesite at the peninsula back in the 1950’s and sought to analyze the recovered core samples. Unfortunately, they were seemingly lost in a warehouse fire just a few years prior.

In 1990, Alan Hildebrand was working with William Boynton and David Kring, studying the K-Pg boundary on the southern peninsula of Haiti. Here, he found what he believed to be ejecta from an asteroid impact in the form of glass spherules (tektites) and shocked quartz grains. These materials were subjected to impact-induced shock melting, where a shockwave from a hypervelocity impact causes rapid and extreme pressure and heating. Much of the sediment and minerals in the ground were turned to glass upon cooling. The unprecedented thickness of the deposits suggested to Hildebrand that the impact had to have been close, either in the Gulf of Mexico or the Caribbean.

A few months later, Hildebrand got wind of Penfield’s peculiar but largely ignored find in the Yucatán Peninsula. It was less than 500 km from their Haiti site which was very promising. Hildebrand contacted Penfield and together they resolved to prove their case. Luckily, they managed to track down a few of the Pemex core samples that had been distributed abroad before the warehouse fire. Upon examination, they found the same evidence of shock melting which suggested an asteroid impact and correlates with the K-Pg boundary. This disproved the volcanic hypothesis in favor of the asteroid impact.

Another interesting feature found at the surface around the crater is a dense semicircular arrangement of cenotes (pronounced say-noh-tay), sinkholes in the ground that lead to groundwater caverns below. In fact, Yucatán Peninsula contains the most concentrated population of cenotes on the planet. These features were known about long before the crater was, sacred to the ancient people of the Mayan civilization, but the true significance of their distribution was unknown. The location of the cenotes correspond with the subsurface crater. It is believed that the asteroid impact fractured the limestone bedrock, creating this network of sinkholes and underground caverns.

Today, this subsurface crater is known as the Chicxulub crater (pronounced chick-shoo-loob). While the center of impact is just off the Yucatán coast, the crater is named after the inland town, Chicxulub Pueblo. In Mayan, the word roughly translates to “tail of the devil.”

The Asteroid

Image credit: NASA / Johns Hopkins APL / Google Earth

Now that we’ve considered some of the key pieces of evidence, though there is much more out there and we will get into that, let’s talk about the cosmic calamity that perpetrated this torrent of death and destruction. Based on the evidence found at the K-Pg boundary and the impact crater, scientists have deduced a number of things about the Chicxulub asteroid.

The asteroid is estimated to have been about 10 to 15 km (6 to 9 mi) in diameter. To put this in perspective, imagine a gargantuan rock about the size of Brooklyn. Certainly larger than Mount Everest. For a more local comparison, over Harford County, it would stretch from Bel Air to Abingdon. These estimates are based on computer simulations that factor in crater dimensions, Earth’s crust composition, energy transfer physics, and the volume and distribution of ejected material, which formed the K-Pg boundary.

Chemical signatures in the geological strata show that Chicxulub was a C-type asteroid, the most common type, making up 75% of known asteroids. These dark, carbon-rich asteroids are remnants of primitive planetesimals from the early solar system and often contain water, organic compounds, and platinum group elements like iridium and ruthenium. The presence of these metals throughout the K-Pg boundary counters claims that Chicxulub was a comet. C-types are mostly found in the outer regions of the asteroid belt between Mars and Jupiter. Recent studies suggest Chicxulub may have been a fragment of a larger asteroid, broken off by a collision. Jupiter, the solar system’s “asteroid wrangler,” may have nudged it into a more eccentric orbit over millions of years, ultimately sending it on a collision course with Earth.

With that being said, let’s get down to it. What follows is a detailed account of the asteroid’s fateful encounter with Earth 66 million years ago, based on the available scientific evidence.

The Approach

Image credit: NASA/JPL-Caltech

Chicxulub would have been a relatively dark object due to its carbon-rich composition. It likely wouldn’t become visible to the naked eye until it was about 6 million km away—15 times the distance of the Moon. From that far, it would have appeared as just another faint “star” among countless others. It’s hard to imagine that such an unassuming speck would soon bring the apocalypse. It also wouldn’t have been obvious much of a hurry this thing was in. Moving at 20 kilometers per second (12 mi/s or 60 times the speed of sound) it would travel the distance between New York City and Los Angeles in just three minutes and twenty seconds. It’s just three days away. In that time, it gradually shifts against the background stars, getting brighter and brighter. Meanwhile, Earth’s creatures carry on, completely oblivious to the false star in the sky that has them in its sights.

Fast forward to the day of reckoning. As the asteroid crosses the Moon’s orbit, it shines as brightly as Vega, the fifth-brightest star. Close enough to be visible through binoculars or a small telescope, its shape is becoming discernible. With the impact site rounding the far side of the planet, the asteroid is only 36,000 km away (less than three Earth diameters or a tenth of the distance to the Moon). It outshines Venus at its brightest, and Chicxulub is no longer just brightening, it’s growing in size. Now larger than Jupiter would appear at its closest, it dominates the sky. With only 30 minutes left, the asteroid transforms from a pinpoint of light to a massive, slowly rotating rock. At one minute before impact, it’s 1,200 km from the surface, appearing as large as the full moon. In the final moments, its size rapidly increases: at thirty seconds, it’s twice the size (2 moons across); at fifteen seconds, four times the size (4 moons across); at five seconds, twelve times the size (12 moons across).

Image credit: AnnieCee

Somewhere in Central America, a handful of Alamosaurs, a species of giant sauropods, are stripping the branches of conifers of their needle-like leaves. They had migrated here from the north to escape the dry season in search of more tropical forests and potential mates. There is a deep rumbling sound like a distant rolling thunder but louder and growing rapidly. The Alamosaurs sway their heads in confusion and let out low, throaty growls at the first tremble felt along their thick hides.

At 100 km above the surface, Chicxulub slams into the Earth’s atmosphere with immense force. The air in front of it compresses and becomes superheated, bursting into white hot plasma. We see very small versions of this effect when grains of dust or small rocks fall to Earth in the form of ‘shooting stars.’ They too are incredibly fast and hot but their mass is insufficient to survive the journey and they vaporize in mid air. That’s why they disappear the moment they beam across the night. This is not the case with Chicxulub.

The sky splits open with light like a second daylight forced into being. The rumble quickly becomes a deafening shriek, tearing through the air and pounding against every surface. The light intensifies just as fast, casting the region in bleached clarity. The Sun pales in comparison, like a candle beside a wildfire. Flash frames of anything with a shadow are burned onto the ground. The asteroid shines so bright that the Alamosaurs’ eyes are permanently seared to blindness. They can’t even see that their bones have become visible through their sizzling, translucent skin. It takes Chicxulub just five seconds to crash through the atmosphere and put an end to the Mesozoic Era.

The Impact

Image credit: Donald E. Davis / NASA

Image credit: Burnt Pineapple Productions

Temperatures produced immediately after the asteroid impact. A thermal pulse would spread across the planet from falling ejecta over the following hours. Image credit: Google Earth

66 million years ago, the Yucatán Peninsula was still emerging from retreating seas. The impact site lay beneath shallow tropical waters—between 100 and 1,200 meters deep—over layers of carbonate rock like dolomite and limestone, with granite continental crust beneath. As the asteroid tears through the atmosphere, the heat is so intense it vaporizes the ocean before the rock even hits.

Chicxulub strikes Earth with the force of a 100-million-megaton bomb—over 6.6 billion times more powerful than Hiroshima and two million times stronger than the Tsar Bomba. A blinding flash, many times brighter than the Sun, sweeps across the western hemisphere for several seconds. When it fades, a 500-kilometer-wide superheated plasma fireball looms in its place. Towering beyond the orbit of the International Space Station, this fiery maelstrom dwarfs any nuclear mushroom cloud. At its core, temperatures exceed 10,000°C, nearly twice the surface of the Sun. Everything nearby is vaporized instantly. Within 1,500 kilometers, what isn’t vaporized ignites into flames, consuming most of Central America, Cuba, and the southern U.S. It takes nearly an hour for the fireball to fully dissipate.

Photograph taken of a flattened Siberian forest following an air burst from the 1908 Tunguska asteroid. That explosion was 3 to 50 megatons. Image credit: Leonid Kulik / Associated Press

There’s two other things that happen at the moment of impact.

First, powerful seismic waves ring the Earth like a bell. Traveling at 6 to 11 kilometers per second—much faster than the air blast—they generate catastrophic earthquakes measuring between magnitude 9 and 11 near the impact site. The violent shaking lasts around fifteen minutes before easing. Within thirty minutes, the waves have circled the globe, reaching the Indian Ocean on the opposite side of the planet. Like the air blast, their intensity tapers off over distance, dropping to around magnitude 6. But when the waves reach the antipode—the point directly opposite the impact—they rebound slightly, triggering a final jolt before fading completely another thirty minutes later. After this global quake subsides, Earth remains seismically unstable. For years to come, the planet will be plagued by frequent earthquakes and widespread volcanic activity.

Simultaneous to the seismic wave is the air blast—an immense shockwave generated by the asteroid’s collision with both the atmosphere and Earth’s surface. It radiates outward in all directions, led by hurricane-force winds exceeding 1,000 kilometers per hour (620 mph). These violent gusts flatten forests and hurl thirty-ton sauropods through the air. Within 45 minutes, the blast reaches modern-day Mexico City, Miami, and Houston with devastating force—lethal within 1,500 kilometers, as if being broiled alive wasn’t already enough. As the atmosphere gradually absorbs the energy, the blast weakens. By the two-hour mark, it reaches Medellín, Albuquerque, and Washington, D.C., still strong enough to rupture eardrums and shatter windows. Farther away, across the globe, it arrives only as a distant, thunderous bang.

Animation credit: University of Arizona, Space Imagery Center, Jake Bailey

Before we expand our scope out to what happens across the planet, let’s go over one more major element at the impact site: the formation of the crater. Due to the asteroid’s size, the crater goes beyond a simple bowl shape. Instead, it forms a peak-ring impact basin, the largest kind. The process that forms this geological structure comes in two main phases: the excavation phase and the modification phase.

Chicxulub punches through the seafloor of the Gulf of Mexico. This instantly vaporizes the asteroid and the incredible energy of the impact is transferred to the Earth. The resulting shockwave compresses, heats and liquifies the surface of the ground below. Within seconds, a 100 km-wide transient cavity lined with impact melt (molten rock) and impact breccia (shattered rock) is created below the gigantic plasma fireball, reaching halfway to the mantle. At the same time, 25 trillion metric tons of earth is launched from the periphery up into the air at incredible speed. These thousands of cubic kilometers of molten material form an ejecta curtain resembling an inverted cone. We will return to these jettisoned fragments shortly.

A few minutes after impact, like when a stone is thrown into a pond, the weakened and viscous floor of the cavity rebounds. A titanic central uplift of subsurface shocked granite forms at the base of the transient cavity, rising high towards the sky. For a few minutes, this uplift is the tallest mountain on the planet. The edges of the cavity collapse into large terraced plateaus called slump blocks, resulting in an inner rim at a 70–85 km radius, and outer ring faults at a 70–130 km radius. The overheightened uplift collapses outward, burying the inner slump blocks and forming the peak ring.

Eight minutes after impact, the final crater settles into place. Most of the shock-melted material falls back into the central basin within the peak ring forming a coherent 3 km-thick melt sheet. Smaller pockets of melt would collect in the annular trough between the peak ring and the crater rim. It would appear like a lake of lava that would eventually cool into a glass-like material. In the hours to come, displaced water would fill the rest with sediment.

The Global Catastrophe

Video credit: MCCONM

Image credit: Science Direct

As mentioned earlier, the asteroid impact launches an immense volume of superheated vapor and debris across the planet. This material forms a curtain of molten rock, rising in an inverted cone around the impact site and expanding rapidly outward. The ejecta spreads in all directions, creating distinct zones of distribution.

Low-energy ejecta consists of massive chunks of Earth’s crust, torn from the surface and hurled outward at relatively slow speeds—2 to 5 km/s. Unlike the high-flying debris, this material stays within the atmosphere and lands within seconds to minutes, blanketing regions up to 4,000 km from the impact. The deposits are thickest near ground zero and thin out with distance. Even at lower velocities, the falling rock is destructive enough to be yet another reason you wouldn’t want to be a dinosaur anywhere near the Gulf of Mexico.

Even more destructive is the high-energy ejecta. Beneath the surface, compressed material rebounds outward in a rarefaction wave. This imparts deep material with enough energy to trigger the crater’s central uplift. High-speed surface tension pulls the molten droplets into spheres, teardrops, or dumbbells—shapes we now recognize as tektites and microtektites scattered along the K–Pg boundary—before they cool and harden in midair. Much of it soars thousands of kilometers high, crossing continents like long-range missiles. Some fragments even reach escape velocity—over 11 km/s—never to return. Scientists believe ancient Earth rocks may still lie scattered across the solar system—hurled there by impacts like this one.

For the ejecta that doesn’t reach escape velocity, the old saying holds true: what goes up must come down. Though much of the debris is small, it returns at hypersonic speeds—5 to 7 kilometers per second. Minutes to hours after impact, these fragments begin raining back through the atmosphere all over the globe. Like the asteroid itself, they tear through the sky, compressing and superheating the air. But unlike a lone shooting star, there are trillions—streaking in all at once. This is what transforms the Chicxulub impact from a bad day in the Gulf into the end of a geological era.

Image credit: Cameron Strandberg

The sky is raining fire. Countless molten spherules tear through the atmosphere like glass bullets, each bursting into a flash of hot plasma. The upper atmosphere surges in temperature by hundreds of degrees, and that heat cascades downward in a blanket of infrared radiation. On a planetary scale, a thermal pulse ripples outward from the impact site as distant ejecta begins to fall back to Earth.

Europe. 45 minutes after impact.

In the moonlit forest, terrified creatures stir as the tremors of a magnitude 8 quake finally subside. Panicked rodents dart through thick underbrush, weaving between the heavy footfalls of a fleeing hadrosaur family. They snort and grunt, thrashing through the foliage as their young struggle to keep up. High above, a faint silhouette glides across a gap in the canopy—untouched by the chaos below. Hatzegopteryx, one of the largest pterosaurs to ever live, rides the wind on a 10-meter wingspan. Its sharp eyes scan the frenzied forest below, hunting for a chance to feed. A straggling hadrosaur catches its eye. It prepares to swoop.

Suddenly, beams of light hiss past, startling the great flyer. It tilts its head to see what appeared like a torrential downpour of fiery hail. An endless barrage of glass spherules—shaped by the atmosphere at hypersonic speed—slice through its leathery wings. It dives—not for prey, but for cover beneath the canopy. It crashes into the underbrush, hoping to ride out the storm. But things are about to get far worse. Temperatures are rising rapidly. Infrared radiation from the skyfall above now showers the region. The sky turns red-hot as surface temperatures soar past 250°C. Vegetation withers, then bursts into flame. The forest becomes a seething inferno. Small mammals and reptiles, insects and worms burrow deep. Frogs, turtles, and crocodiles slip into the water. It won’t save them all—but it gives them a chance.

An hour and a half after impact, every continent on Earth has been affected by falling ejecta. 70% of the world’s forests are burning and the entire planet is shrouded in thick dust. A layer of charcoal and soot produced by these flames has been found at the K-Pg boundary on every continent. The vast majority of the world’s dinosaurs, especially the larger ones, have been thoroughly eliminated. And yet, there is still one more horror to befall the survivors on just the first day.

Image credit: Wikimedia Commons

The first ten minutes of the tsunami were simulated by a large computer program called a hydrocode, which models details of complex fluid flows. The left border represents the point of impact. Image credit: AGU Advances

Evidence found across the world suggests that the Chicxulub asteroid impact produced a global megatsunami 30,000 times more energetic than the 2004 Indian Ocean earthquake tsunami, which killed over 230,000 people.

The asteroid vaporizes water at the impact site, forcing the surrounding ocean upward and outward into a massive 4.5-km (2.8-mi) transient wave. This puts the wave at over five times the height of the Burj Khalifa—the tallest building on Earth. It would crest just above the summit of Mount Rainier. Despite its terrifying height, it lasts only a few minutes. Gravity and a barrage of falling ejecta pull the wave down, disrupting its mass and dispersing its energy. About ten minutes later, as the larger ejecta settles, the tsunami’s energy carries on as a 1.5-kilometer-high traveling rim wave. Still towering—nearly twice the height of the Burj Khalifa—the wave gradually fades as it radiates across the Gulf in concentric rings.

Moving at a speed of about 250 meters per second, the tsunami lags behind the air blast and falling ejecta. It takes until about an hour after impact for the first waves to reach the coasts of Mexico to the west and the southern United States to the north (about 1,000 km from the impact site). By this point, the waves would have shrunk down to between 100 and 300 meters in height. This is taller than either the Statue of Liberty or the Eiffel Tower, respectively. That would still be an absolutely horrifying sight to behold, signaling the doom of any ground-dwelling creatures remotely near those coasts.

The tidal wave approaches as if trying to claw its way out of the sea. From the beach you can see the Sun’s sinking visage reflecting off this colossal wall of water stretching from one horizon to the other. When it makes landfall it crashes down onto the beach with the weight of entire mountains. It rips hundreds of feet of sediment and rock from the coast. Cypress, redwood and palm trees already flattened by the air blast and set ablaze by the scorching heat of the impact and falling ejecta are extinguished by the surge of seawater crashing across the land like a giant high-speed bulldozer.

The tsunami reaches 100 km inland before the backwash sweeps continental debris with it back into the Gulf of Mexico and deposited into seafloor channels. Megaripples have been found buried underneath Louisiana, large fossilized bedforms created by powerful water flow which then receded. Evidence found off the coast of Arroyo el Mimbral, Tamaulipas, Mexico suggests that backwash from the tsunami dragged plant debris from a mangrove ecosystem out to sea and buried it underneath with additional debris.

This NOAA simulation shows the propagation of tsunami waves from ten minutes after impact to two days after impact. This is a supplement of the hydrocode simulation shown earlier. Notice the complex reflection and refraction patterns after the tsunami goes global. Video credit: National Oceanic and Atmospheric Administration (NOAA)

The tsunami quickly escapes the Gulf of Mexico, rippling into both the Atlantic and Pacific Oceans. As it spreads, its height decreases with distance. Six to eight hours after impact, ocean swells reach the western coasts of Europe and Africa. As the tsunami nears shore, it slows and compresses—a process called wave shoaling. It quickly transforms a subtle swell into a towering 15–20 meter wave. Still the size of buildings and powerful enough to tear up coastlines thousands of kilometers from the impact site. In the Pacific, it strikes Asia and Australia twelve to twenty-four hours later. There, waves strike at heights of 5–10 meters (16–33 feet). In shallow bays and narrow inlets, shoaling can dramatically amplify wave heights.

The first global simulations of the Chicxulub impact tsunami show how it may have propagated, supported by geological evidence from over a hundred sites worldwide, from New Jersey to New Zealand. Geologists studied rock layers formed during the impact, especially along coastlines in the tsunami’s path. They found thick, chaotic sediment layers, broken debris, and storm-like deposits mixing marine and land materials—clear signs of violent water movement. In some places, entire layers are missing, likely stripped away by the tsunami. Many sites are also littered with shock-melted ejecta.

Any creature caught in the coastal surges would have been wiped out by the wave’s blunt force, drowned, or buried under sediment. Even small, burrowing animals seeking shelter from the thermal pulse were torn from their hideaways. Coastal habitats, like turtle nests, were completely destroyed. The tsunami was the final major trauma of the impact event—but only the beginning of a much longer battle of attrition.

The Impact Winter

The landscape in the immediate aftermath would have looked much like this, except much darker and more smoldering. Image credit: U.S. Fish and Wildlife Service Northeast Region

The first day of the Cenozoic Era feels more like twilight. A transient red glow of sunlight barely pierces through thick dust and ash choking the sky, while the horizon vanishes into an endless brown-grey haze. The once-vibrant sounds of chirping insects, bellowing dinosaurs, and shrieking pterosaurs are gone, replaced only by crackling wildfires and howling winds. At night, the world is plunged into pitch black; dust blots out the stars and moon, leaving only the light of flickering flames.

The asteroid impact and resulting firestorm injected immense amounts of dust, soot, and sulfates into the atmosphere. For the first year, sunlight is reduced by more than 80%. One of the biggest consequences of this is the halting of photosynthesis, which is how plants convert sunlight into energy. Studies estimate this shutdown lasts up to two years, causing widespread plant death—especially among deciduous, tropical, and flowering species—and triggering a food chain collapse. Herbivores starve without plants, and carnivores follow.

Modern-day Montana. One week after impact.

Amidst the smoldering remains of a once-lush woodland, a snout pokes out from the dark of a narrow crevasse in the side of a mountain. The intense heat seems to have mostly subsided, leaving a pungent, bitter odor pervading the air. An Acheroraptor emerges into the new world for the first time. Resembling its Mongolian cousin, the Velociraptor, this feathered dinosaur is quite possibly the last dromeosaur in existence. It has spent the last week hiding from the firestorm, sustaining on the few beetles that scurry by and trying to conserve its energy. It can no longer remain inside. Its stomach is twisting with hunger and will not last much longer without a proper meal. It is too weak to hunt and its prey remains in hiding. Luckily, the region is littered with the charred carcasses of large dinosaurs.

The Acheroraptor timidly patrols the desolate, ash-covered landscape until it spies a large lump through the haze. It approaches with caution. A dead Tyrannosaurus. It’s unusual to see one this far up the mountains. It must have been driven here by the chaos of the disaster. The raptor climbs atop the creature’s thick, charred hide and begins picking away at it with quick, nipping bites. The raptor spent its life being chased off by these colossal beasts. Now, one of them would provide life-saving sustenance. Despite this lucky break, it won’t last. Even when cooked by thermal radiation, the dead will soon decay. If the Acheroraptor doesn’t starve, it will collapse from respiratory illness. It will be lucky to make it through the month, especially with what’s coming next.

Image credit: NASA

After the wildfires burn out, global temperatures plummet as sunlight struggles to reach the surface. This marks the start of what’s known as an impact winter. While we can’t be certain exactly how far the temperature dropped, we can be sure it was dependent on latitude. This matters because the Sun’s rays strike the Earth at different angles depending on latitude. Near the equator, sunlight arrives more directly, concentrating energy in a smaller area and producing more heat. Toward the poles, sunlight hits at a slant, spreading the same energy over a wider area, which leads to cooler temperatures. This is why the Earth’s axial tilt causes seasons. In the midst of an impact winter where significant dust and soot are blocking sunlight, latitude will exaggerate the effect.

Near the equator, there is likely a milder drop of 5-10°C (9-18°F). But even this disrupts tropical forests, which rely on steady warmth and sunlight. At more mid-latitudes, there’s a steeper drop in temperature of 10-15°C (18-27°F). Many temperate forest plants that survived the initial fires are later stunted or killed by cold and drought. Polar latitudes experience the most significant temperature drops, possibly 20°C (36-45°F) or more. These regions already get the least sunlight—and for half the year, none at all. Add the dust and soot, and it becomes a time of profound cold and darkness.

Over the following months, the northern hemisphere is thrust into a brutal deep freeze. Cooling is more severe here, where the asteroid’s ejecta was thickest and most of the world’s landmasses are concentrated (which are more vulnerable to temperature changes than oceans). North America, Europe, and northern Asia turn into bitter, desolate tundras locked in near year-round snowfall. The scorched jungles of the Amazon, Congo, and Southeast Asia grow cold, dark, and dry—but don’t freeze. Patagonia (southern tip of South America) likely freezes. Australia, though similarly placed in latitude, was farther from the impact and—despite burning and darkness—may have escaped full glaciation.

As the aerial regolith sinks from the stratosphere into the troposphere, rain begins flushing it from the sky. However, vaporized gypsum from the Gulf seabed reacts with water vapor to form sulfuric acid rain, which persists for years. On land, acid rain scars plant tissue and strips soil of nutrients, stifling growth and reproduction. Near ocean surfaces, it devastates plankton populations. A clay layer in a Dutch cave, rich in fossilized plankton shells, preserves isotopic evidence of ocean acidification. As plankton collapse, fish starve en masse—followed by the extinction of their larger predators, like the mosasaurus. Deep-sea life, however, appears to have been relatively sheltered.

The world is frozen in time by a dark veil of ash, ice and silence. Two long years drag on as small creatures timidly scour the wasteland for food and kin, driven only by the instinct to survive. Then, one day, the Sun peeks through the overcast for just a moment. The next week it does again… until the moments become minutes, and the minutes become hours. Slowly, the sky lightens—not blue, but a bruised gray that hints at something brighter. The thick shroud of ejecta dust, once suspended high in the stratosphere, begins its long descent, settling in a fine, grimy film over the stale earth. Shadows reappear, faint and fractured, crawling across snow-covered ash. In the light of day, time stirs, and the Earth, long entombed, begins to breathe once more.

It takes fifteen to twenty years for the atmosphere to clear and normal sunlight to return again but the old world never will. When the dust has settled, 75% of all species of plants and animals on the planet have gone extinct. The age of reptiles has ended. However, buried amidst the bones of the old world, the seeds of a new world have been planted.

Earth’s Resilience

Artist impression of the Patagonian region of South America in the Danian Age. Image credit: Barreda VD / Cúneo NR / Wilf P / Currano ED / Scasso RA / F. Guillén

Earth begins to warm. In fact, for tens of thousands of years, global temperatures rise beyond pre-impact levels, driven by an atmosphere saturated with greenhouse gases like carbon dioxide. The tropics grow increasingly hot and humid, while the poles remain temperate and the ice caps vanish. The scarred remains of dead forests are rapidly colonized by ferns and fungi. Both were remarkably resilient to the dark, cold, dry, and nutrient-poor conditions of the impact winter. Reproducing through hardy spores carried on the wind, they rapidly colonize new areas, becoming some of the first life to reclaim the surface. In time, flowering plants, deciduous trees and broadleaf evergreens rebound—though conifers never return to their former dominance.

The quiet rebirth of the planet’s forests and grasslands, determined to grow beyond their patchy footholds, marks the first step in a larger resurgence. Beneath the fledgling canopies, small creatures stir from the shadows. Many spent hundreds of millions of years confined to the margins, active only under the cover of night. Mammals. Some are the size of badgers but most are no larger than rats. They emerge into the daylight to find a world transformed. The thunderous march of giants is now silent. Fields of grass are no longer grazed to stubble. The skies, once patrolled by the silhouette of soaring predators, are now clear.

A skeleton of Paraceratherium, one of the largest land mammals to ever live, on display in the Moscow Paleontological Museum. Image credit: MikSed

Freed from the constant threat of larger, swifter predators, mammals spread across the land, filling vast, unclaimed habitats. They didn’t just grow in number—they grew in size. Within 100,000 years of the asteroid impact, once-rare opossum-sized mammals became common. In a million years, sheep-sized predators like Ankalagon emerged. Ten million years later, cow-sized herbivores like Barylambda roamed the Earth. By thirty million years, giants like the 20-ton, hornless rhino Paraceratherium walked the plains of Asia. Today, the largest mammal isn’t on land—it swims. At 30 meters long and weighing 200 tons, the blue whale is not just the largest mammal, but the largest animal in Earth’s history. Mammals have since adapted to nearly every niche: horses and elephants graze, monkeys and squirrels climb, bats fly, dolphins and otters swim, rabbits and prairie dogs burrow. Jaguars thrive in the tropics, wolves in temperate zones, and polar bears in the icy extremes.

It does beg the question, though. Did any dinosaurs survive?

Dinosaur fossils are reported to have been found above the K–Pg boundary, such as a hadrosaur femur in the Hell Creek Formation in North America. While this might suggest that some non-avian dinosaurs survived the asteroid impact for thousands or even millions of years, there’s no conclusive evidence to support that. It’s not impossible that some dinosaur species may have persisted in isolated pockets, but most paleontologists attribute these finds to “reworking”—where older fossils are unearthed by erosion and reburied in younger sediment layers.

That said, some dinosaurs did survive the Chicxulub impact—and they still live among us. Or rather, they fly. These are the avian dinosaurs, the ancestors of modern birds. Birds actually evolved from dinosaurs long before the Chicxulub asteroid hit the Earth in the Late Jurassic. Archaeopteryx is widely regarded as the first true bird species. That bird perched on your backyard fence? It’s a distant relative of theropods like Tyrannosaurus and Velociraptor. If that seems hard to believe, search images online of a cassowary or a shoebill stork and take a close look. It’s pretty remarkable. These creatures are our remaining connection to a lost era and evidence of the relentless resilience of life on this one-of-a-kind planet.

It Happened Before; Will It Happen Again?

This map shows the location of confirmed impact structures on Earth. As of 2019, the database lists 190 confirmed impact sites. Image credit: Earth Impact Database

Dinosaurs ruled the planet for 180 million years. Then, in the span of a single day, their reign was over. But that cosmic killer from space wasn’t alone. There are probably billions to trillions of asteroids and comets floating around out there in the solar system. Should we be worried?

Meteors hit Earth literally all the time. Whenever you see a shooting star, that is a meteor burning up in Earth’s atmosphere. Earth is constantly moving through space in its orbit, sweeping up cosmic debris leftover by some passing asteroid, comet or the remnants of some collision. Imagine a truck (Earth) driving down the road (orbiting the Sun) where a swarm of bugs (dust and rocks) are buzzing around (floating through space) and they get splattered on the windshield (burn up in Earth’s atmosphere). It happens millions and millions of times each day. But those shooting stars are actually just tiny dust particles and pebbles. They are too small to survive the extreme heat and disintegrate immediately. Bigger objects hit Earth too but less frequently.

Here is how often asteroids of different sizes hit the Earth (on average).

Smaller asteroids are not massive enough to make it to the surface and explode mid-air, producing a powerful air burst:

• Asteroids with a 5 meter (16 feet) diameter enter Earth’s atmosphere about once a year. They produce a 1 kiloton air burst.

• Asteroids with a 20 meter (65 feet) diameter enter Earth’s atmosphere about twice every century. They produce a 500 kiloton air burst. This is equivalent to the 2013 Chelyabinsk asteroid.

• Asteroids with a 50 meter (164 feet) diameter enter Earth’s atmosphere about every 750 years. They produce a 15 megaton air burst. This is equivalent to the 1908 Tunguska asteroid.

Larger asteroids survive the atmosphere and strike the surface, causing significant destruction and leave a crater:

• Asteroids with a 100 meter (330 feet) diameter strike Earth every 5,000 years. They produce a 75 megaton blast and leave a 2 km-wide (1.25 mi) crater.

• Asteroids with a 300 meter (980 feet) diameter strike Earth every 75,000 years. They produce a 2,000 megaton blast and leave a 8 km-wide (5 mi) crater. This is comparable to Apophis, an asteroid expected to pass very close to Earth in 2029.

• Asteroids with a 1 km (0.62 mi) diameter strike Earth every 500,000 years. They produce a 75,000 megaton blast and leave a 20 km-wide (12.5 mi) crater.

• Asteroids with a 5 km (3 mi) diameter strike Earth every 20 million years. They produce a 12.5 million megaton blast and leave a 100 km-wide (62 mi) crater.

• Chicxulub was the last time a 10 km (6 mi) diameter asteroid hit Earth 66 million years ago and we all know how that turned out. They are estimated to strike Earth every 250-500 million years.

Needless to say, an asteroid the size of Chicxulub is not expected to arrive anytime soon. We have more to fear from smaller, more frequent asteroids. There are no officially recorded deaths of people killed by meteor impacts (possibly three during the 1908 Tunguska event) but there have been people hurt. About 1,500 people were injured by the Chelyabinsk asteroid air burst over Russia in 2013 (18-meter asteroid).

All this being said, we live in a much different time than we did even just a few decades ago. Technology is advancing faster and faster. Our ability to spot smaller asteroids from further away and calculate their trajectories is growing rapidly. In 2022, NASA launched the DART mission which sent a space probe out to the asteroid belt and intentionally collided it with an asteroid in an attempt to deflect its path. In 2024, the ESA launched the Hera mission to investigate the aftermath. We may be entering an era where humans no longer have to fear cosmic collisions of the like that killed the dinosaurs.

The Deccan Traps: A Plausible Alternative?

Image credit: National Science Foundation / Zina Deretsky

There are debates amongst paleontologists and geologists and other interested parties about the nature of the extinction of the dinosaurs that continue to this day. Some scientists posit that dinosaurs were not wiped out by a large meteor but by something else that beat it to the punch.

The theory is that an enormous volcanic region in western Indian known as the Deccan Traps generated significant and sustained volcanic activity before and after the Chicxulub impact. These eruptions would have spewed massive amounts of carbon dioxide and sulfur dioxide into the atmosphere over the course of hundreds of thousands of years. These plumes of toxins would have blocked sunlight, acidified oceans and caused climate instability via the greenhouse effect.

Radiometric dating techniques due suggest that intense eruptions began shortly before and continued after the mass extinction event. Geological records showing rapid climate change do correlate with the effects of the eruptions (a cooling period followed by a warming period). The effects of sulfur and carbon dioxide on the acidification of the oceans are also consistent with the theory. Fossil evidence from plankton hints at possible ecosystem decline prior to the asteroid impact. Elevated levels of mercury, a common byproduct of volcanic eruptions, have been found in sediment layers around the world at the K-Pg boundary.

The evidence is compelling but the Chicxulub asteroid impact is pretty much undeniable. This has led many scientists to take the position that both events contributed to the extinction of the dinosaurs. Whether Chicxulub was the sole progenitor of the dinosaurs’ doom or merely struck the killing blow, it is incredibly clear that the dinosaurs were not long for this world.