The Chicxulub Crater
The Impact That Ended the Age of Dinosaurs
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- Earth Sciences
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The book details how scientists discovered the crater's unique geology, including the distinctive impact rocks and shocked quartz found at the site. Chapters explore the massive effects of the collision, from the initial impact to the global climate changes that followed. The work covers the astronomical origin of the impactor and compares this event to other mass extinctions.
This comprehensive guide will interest anyone curious about Earth's most famous impact event, from students to professional geologists studying the K-Pg boundary and its aftermath.
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In the late 1970s, a geologist named Walter Alvarez and his father, Luis Walter Alvarez—a Nobel Prize winner—put forward the idea that the extinction of the dinosaurs was caused by an asteroid hitting Earth. They found evidence in a thin clay layer at the boundary between the Cretaceous and Paleogene periods in Gubbio, Italy. That layer had an unusually high amount of iridium, up to 160 times more than normal. The Alvarezes believed this element came from an asteroid that was vaporized on impact, sending debris across the planet. At the time, many scientists were skeptical, especially because there were few fossils near the boundary layer, which they thought suggested a slow extinction instead of a sudden one.
In June 1980, the Alvarezes published their paper on the iridium anomaly in Science, with Frank Asaro and Helen Michel from University of California, Berkeley, contributing to the work. A month earlier, in May 1980, Jan Smit and Jan Hertogen had already reported similar findings from Caravaca, Spain, in Nature. These reports sparked widespread interest in the K–Pg extinction, leading to over 2,000 papers published during the 1980s. No known impact craters matched the age and size needed, so scientists began searching for one. In 1981, a cross-discipline meeting was organized to address the mystery, though unknown to those involved, evidence of the crater they were seeking was presented the same week — but largely went unnoticed by the scientific community.
In 1978, geophysicist Glen Penfield and Antonio Camargo were part of a team surveying the Gulf of Mexico for oil, working for Pemex. Penfield analyzed data to identify potential drilling sites. During his work, he noticed certain magnetic anomalies and estimated their depth. He then gathered gravity maps from the 1940s and matched them with the magnetic readings. The comparison revealed a shallow, circular pattern—what he described as a “bullseye”—spanning 180 kilometers in diameter. To Penfield, this clearly pointed to an impact crater. Ten years earlier, another worker named Robert Baltosser had seen the same signs but was blocked by company policy from revealing his conclusion.
Penfield took his findings to Pemex, who rejected the idea that the feature was an impact crater and instead favored explanations linking it to volcanic activity. The company withheld specific data but let Penfield and Camargo present their work at the 1981 Society of Exploration Geophysicists conference. That conference drew few attendees, so the report attracted little notice, as many experts were attending the Snowbird conference instead. A journalist from the Houston Chronicle, Carlos Byars, who was familiar with Penfield and had viewed the gravitational and magnetic data firsthand, wrote a front-page story on the claim, though the news did not reach many people.
Penfield had plenty of geophysical data but no rock cores or other physical evidence to prove an impact had occurred. He knew that Pemex had drilled exploratory wells in the region, and in 1951 one well reached a layer of andesite about 1.3 kilometers down. At the time, the finding was dismissed as a lava dome—something not typical of the area's geology. Encouraged by William C. Phinney, who curated lunar rocks at the Johnson Space Center, Penfield tried to secure samples that would support his hypothesis. He attempted to retrieve site samples but was told they had been lost or destroyed. Visiting the drill sites again turned up nothing. So he published his findings and returned to his work at Pemex. Later, after seeing the 1980 Science paper, he wrote to Walter Alvarez about the Yucatán structure, but received no response.
Alvarez and other scientists searched for the crater despite looking in oceans based on a mistake about glassy spherules from the K–Pg boundary that led them to think the impactor had hit open water. Meanwhile, at the University of Arizona, graduate student Alan R. Hildebrand and his adviser William V. Boynton searched near the Brazos River in Texas. They found greenish-brown clay with extra iridium, shocked quartz grains, and small glass beads that looked like tektites. They also saw thick, jumbled rock deposits suggesting an impact event had moved material from one place to another. These deposits were found in many places but seemed especially concentrated in the Caribbean Basin at the K–Pg boundary. When Haitian professor Florentine Morás thought he'd found signs of an ancient volcano on Haiti, Hildebrand guessed it might instead be evidence of a nearby impact. Tests on samples from the K–Pg boundary turned up more tektite glass—only formed by asteroid impacts or high-yield nuclear explosions.
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A 2013 study in Science gave the impact its most precise date yet: 66,043,000 years ago, give or take eleven thousand years, with even greater uncertainty when systematic error is considered. That estimate came from argon–argon dating of tektites from Haiti and bentonite layers in Montana. A follow-up study in 2015 supported that date using tephra from lignite beds in the Hell Creek Formation. Then in 2018, researchers dated spherules from Gorgonilla Island, Colombia, and got a slightly different result: 66,051,000 years ago, plus or minus thirty-one thousand. The impact likely happened during spring in the Northern Hemisphere, based on isotope patterns in sturgeon and paddlefish bones found at the Tanis site in North Dakota—remains from a sedimentary layer that formed within hours of the strike.
The impact occurred in what was once a shallow sea, on a marine carbonate platform. At the time of the collision, water depths ranged from about 100 meters along the western edge of the future crater to more than 1,200 meters near the northeastern rim, with the center estimated at around 650 meters deep. The seafloor beneath was made up of layers of Jurassic–Cretaceous sediments, roughly 3 kilometers thick. These rocks were mostly limestone and dolomite, with some evaporites like anhydrite and small amounts of shale and sandstone. Underneath lay about 35 kilometers of continental crust, including igneous basement rock such as granite.
The object that struck Earth was about ten kilometers across—large enough that if it had been placed at sea level, it would have towered over Mount Everest. In 2021, scientists estimated the impactor was moving at around twenty kilometers per second, coming in at an angle between forty-five and sixty degrees from the northeast.
The energy released by the impact that ended the age of dinosaurs is estimated to be between roughly 10 to the 23rd joules and 10 to the 25th joules. That’s the equivalent of tens of millions to billions of megatons of TNT. Scientists have debated the exact amount, but the numbers are staggering, reflecting the immense force of the event that changed Earth forever.
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The Chicxulub impact created winds faster than 1,000 kilometers per hour near the center, carved a transient cavity 100 kilometers wide and 30 deep, which later collapsed into a crater mostly under the sea. That crater now sits buried beneath about 1,000 meters of sediment. The crash, water filling the hole, and related earthquakes caused massive tsunamis over 100 meters tall, with one simulation suggesting waves may have reached 1.5 kilometers high immediately after impact. These waves scoured the seafloor, leaving behind ripples in what is now Louisiana—average wavelengths of 600 meters and heights of 16 meters, the largest ever documented. The disturbance moved through Earth’s crust and across the ocean floor, reaching areas now known as Texas and Florida, possibly affecting sediments up to 6,000 kilometers from the point of impact. A seismic event with a moment magnitude between 9 and 11 followed the collision.
A cloud of hot dust, ash, and steam spread from the crater, with 25 trillion metric tons of material blasted into the atmosphere. Some of it left Earth entirely, scattering through the Solar System, while the rest fell back, vaporizing on re-entry. The heat from the ejecta ignited wildfires that covered nearly 70% of Earth’s forests. Even creatures hundreds of kilometers away felt the impact, and areas now part of Mexico and the United States were devastated. Fossil evidence from a layer just 10 centimeters thick in New Jersey, 2,500 kilometers from the crash site, shows an instant extinction. In 2019, research from the Hell Creek Formation in North Dakota confirmed widespread species die-off, matching what would be expected from the impact event.
The impact created a global climate catastrophe, in part because the shallow water at the crash site meant sulfur-rich gypsum was vaporized and sent into the atmosphere. This caused sudden cooling and disrupted the food chain. Some researchers believe the event also sparked a massive underground hydrothermal system, offering a refuge for life to rebound. In 2008, scientists used seismic images to find that the impactor actually hit deeper water than earlier thought, which may have increased sulfate aerosols from more water reacting with vaporized anhydrite. That could have made the climate crash even faster and worse, possibly triggering acid rain.
The crash sent dust and particles into the air, covering Earth for years—possibly as long as a decade—making it hard for life to survive. The impact broke apart carbonate rocks, releasing carbon dioxide that caused a sudden greenhouse effect. A large oil field at the site may have burned, adding soot to the atmosphere and blocking sunlight even more. For many years, maybe longer, the surface of Earth would have grown cold as light was kept from reaching it. Plants couldn’t photosynthesize, which disrupted the whole food chain. But according to a model by Lomax et al. (2001), over time, net primary productivity might have risen because of the high carbon dioxide levels.
The crash left behind more than just a hole in the ground. Over time, the impact shaped the land into what’s known as the Yucatán sedimentary basin. This change in the landscape eventually made it possible for people to live in an area where water is hard to find. The region’s conditions became suitable for human settlement because of what happened so long ago.
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Since the discovery of the Chicxulub Crater, scientists have gathered two seismic reflection datasets over its offshore areas. Older 2D seismic data, originally collected for oil exploration, has also been used. In October 1996, the BIRPS group recorded a set of three long 2D lines covering 650 kilometers total. The longest, called Chicx-A, ran parallel to the coast, while Chicx-B and Chicx-C were oriented NW–SE and SSW–NNE respectively. The data included not only standard seismic imaging but also onshore recordings that enabled wide-angle refraction techniques.
In 2005, scientists gathered more seismic data to map the Chicxulub Crater, extending the total length of deep-penetration 2D surveys to 2,470 kilometers. Using ocean bottom seismometers and land stations, they performed 3D travel time inversion to better understand the crater’s underground structure, focusing on the offshore peak ring to identify potential drilling sites. At the same time, gravity measurements were taken along 7,638 kilometers of profiles. This work was funded by the National Science Foundation and the Natural Environment Research Council, with support from the National Autonomous University of Mexico and the Centro de Investigación Científica de Yucatán.
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In the years following early exploration work by Pemex, researchers gathered valuable information from core samples taken during oil drilling on the Yucatán peninsula. In 1995, UNAM completed eight full-cored boreholes, three of which reached deep enough to sample the material ejected during the impact, including UNAM-5, UNAM-6, and UNAM-7. Then, between 2001 and 2002, a scientific drilling project was carried out near Hacienda Yaxcopoil under the International Continental Scientific Drilling Program. The resulting borehole, commonly called Yax-1 or Yaxcopoil-1, went down 1,511 meters, passing through 100 meters of impactites. The Comisión Federal de Electricidad also joined with UNAM to drill three more fully-cored holes, with one, BEV-4, reaching the ejecta layer as well.
In 2016, a team from the United Kingdom and the United States successfully drilled a borehole called M0077A as part of Expedition 364 with the International Ocean Discovery Program. They recovered the first offshore core samples from the peak ring in the center of the Chicxulub crater. The drill reached a depth of 1,335 meters below the seafloor.
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The Chicxulub crater's structure comes mostly from underground data, and it's shaped like a series of circles within circles. The outer ring, found through seismic scans, stretches up to 130 kilometers from the center and shows normal faults where the ground drops toward the middle, marking the edge of major crustal changes. This makes it one of Earth's three largest impact sites. Inside that is the main crater rim, also called the inner rim, which matches a ring of cenotes on land and a strong gravity change. That ring spans 70 to 85 kilometers across. Between the inner rim and the peak ring lies the terrace zone, full of faulted blocks falling inward. The peak ring itself is around 80 kilometers wide, standing 400 to 600 meters high in the west and northwest, and about 200 to 300 meters in other directions. At the center, the crust sits above a zone where Earth's mantle was pushed up, making the boundary between crust and mantle shallower by about one to two kilometers than usual.
The ring structures surrounding the Chicxulub Crater are most clearly defined toward the south, west, and northwest, gradually fading as you move toward the north and northeast. Scientists believe this pattern reflects the varying water depths at the time of the impact. Areas where the ocean was much deeper than 100 meters—about 300 feet—show less distinct rings, while shallower regions preserved more pronounced features. This difference in ring clarity gives clues about how the impact site interacted with its marine environment.
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Before the impact, the area now known as the Yucatán was underlain by a basement of granitic rocks, part of what's called the Maya Block. This block sits at the edge of the ancient Gondwana continent, and its structure comes mostly from drilling around the Chicxulub crater and analyzing material ejected far from the impact site. The rocks above the basement are mainly Cretaceous limestones, with red beds of uncertain age lying on top. Below those, an unconformity marks a gap in time. Zircon dating suggests the basement includes crust formed during the Grenville orogeny, with younger arc-related igneous rocks from the late Ediacaran period. In the peak ring area, a borehole found Carboniferous granitoids dated at 326 ± 5 million years ago, with an adakitic composition suggesting slab detachment during the Marathon-Ouachita orogeny, part of the larger collision that formed Pangaea.
The area now known as the Yucatán Trough was once home to a Cretaceous basin, a geological feature that shaped the region's rock layers over time. Red beds, some up to 115 meters thick, sit atop older granitic rock, especially in the south, and are believed to be from the Triassic through Jurassic periods, possibly extending into the Lower Cretaceous. Below them lies a sequence of the Lower Cretaceous, starting with dolomite and interbedded anhydrite and gypsum, then shifting to limestone with dolomite and anhydrite toward the top. These layers reach up to 1,675 meters in thickness. Above that, the Upper Cretaceous consists mainly of platform limestone, mixed with marl and anhydrite, varying from 600 to 1,200 meters thick.
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The most common impact rocks found around the Chicxulub crater are suevites, which appear in many of the boreholes drilled in the area. Most of these suevites were resedimented shortly after the impact, when ocean water surged back into the crater. This process created a layer of suevite that spread from the inner part of the crater all the way to its outer edge.
The central part of the Chicxulub Crater is thought to be filled with impact melt rocks, reaching up to three kilometers in thickness. Samples studied show compositions similar to the underlying basement rocks, though some show signs of mixing with carbonate material likely from Cretaceous carbonates. Analysis of melt rocks from the M0077A borehole reveals two types: an upper impact melt, or UIM, which contains clear carbonate components shown through its chemistry and rare limestone fragments, and a lower impact melt-bearing unit, or LIMB, which has no carbonate presence. The distinction is believed to stem from the original impact melt, represented by the LIMB, becoming mixed with shallow crustal materials either falling back into the crater or brought up during the resurgence that formed the UIM.
In the peak ring borehole, a rock called "pink granite" tells the story of extreme forces during the crater’s birth and the rise of its central peak. This granitoid stands out for its low density and slower P-wave speed compared to typical basement granites. Core samples from M0077A show how it changed over time: at first, fractures spread through the grain boundaries; then, many shear faults developed; later, zones of crushed rock—cataclasite and ultra-cataclasite—formed; and finally, some ductile shearing left its mark. These changes suggest that the impact began with acoustic fluidization, followed by faulting that brought melt-filled zones to the surface.
Deep beneath the ocean floor, drilling into the peak ring of the Chicxulub crater revealed signs of an enormous hydrothermal system. This system altered around 1.4 × 105 km3 of Earth’s crust and persisted for hundreds of thousands of years. Such findings may lend support to the idea that life on Earth began through impacts, especially during the Hadean eon, when the planet was constantly bombarded by asteroids much larger than the one responsible for the Chicxulub event.
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After the initial blast of the impact settled, the area around what is now called the Chicxulub Crater slowly returned to its normal state, a shallow sea where carbonate rocks had been building up for millions of years. Over time, layers of marl and limestone accumulated, reaching about 1,000 meters thick. These deposits, dating back to the Paleocene, contain the boundary between the Cretaceous and Paleogene periods, known as the K–Pg boundary. This boundary is found much deeper inside the crater than it is in the surrounding region.
In the Yucatán, the edge of the crater shows up today as groups of cenotes—sinkholes that reveal how water moves through the ground. These underground channels carry water from the southern recharge areas down to the coast, flowing through a system shaped like a karstic aquifer. By looking at where the cenotes appear, scientists can see they connect directly to the hidden rim of the crater below, likely because the rock there has more cracks and breaks than other areas.
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There is broad agreement that the object responsible for the Chicxulub crater was a C-type asteroid with a composition similar to carbonaceous chondrites, ruling out a cometary origin. In 1998, a meteorite roughly 2.5 millimeters across was discovered in deep-sea sediment from the North Pacific, at the base of the K-Pg boundary iridium anomaly, and was suggested to be a fragment of that impactor. Its analysis indicated it aligned with the CV, CO, and CR groups of carbonaceous chondrites. Isotopic data from ruthenium in impact layers further supported a carbonaceous chondrite origin. A 2021 paper, based on excess chromium isotope 54Cr and ratios of platinum group metals found in marine impact layers, pointed toward CM or CR types. Then, in 2026, analysis of nickel isotopes narrowed the classification to the CO group.
In 2007, a Nature report suggested the Chicxulub asteroid originated from a collision 160 million years ago in the asteroid belt, when a 170-kilometer body struck a 60-kilometer object, creating the Baptistina family, with 298 Baptistina as its largest member. The authors—William F. Bottke, David Vokrouhlický, and David Nesvorný—proposed the impactor was part of that group. But in 2009, a spectrographic analysis showed 298 Baptistina has a composition more typical of an S-type asteroid than the carbonaceous chondrite expected from the Chicxulub impactor. Then, in 2011, data from the Wide-field Infrared Survey Explorer pushed the collision date back to about 80 million years ago, leaving only 15 million years for the process, which takes much longer. Another idea in 2010 pointed to asteroid 354P/LINEAR, a member of the Flora family, as a possible remnant. In 2021, a numerical simulation study concluded the impactor likely came from the outer main part of the asteroid belt.
Some have suggested the object that wiped out the dinosaurs wasn’t an asteroid but a comet. In 1984, two papers proposed it came from the Oort cloud, and in 1992, scientists suggested tidal forces could increase the rate of comet impacts. Then in 2021, Avi Loeb and a colleague wrote in Scientific Reports that the impactor might have been a fragment from a disrupted comet. But a rebuttal in Astronomy & Geophysics argued that the global iridium deposit—between 2.0×10⁸ and 2.8×10⁸ kilograms—was far too massive for such a comet. They also said Loeb’s team had exaggerated how often comets hit Earth. The rebuttal concluded that all evidence supports an asteroid impact, effectively dismissing a comet. Ruthenium isotope ratios in the impact layers further confirm this.
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