The Chicxulub crater is the impact crater buried underneath the Yucatán Peninsula in Mexico. It was formed by a large asteroid or comet about 10 to 15 kilometers (6 to 9 miles) in diameter that collided with Earth around 66 million years ago at the end of the Cretaceous Period. The collision caused major global climate changes and led to the extinction of the dinosaurs and about 75% of all species on Earth. The crater is estimated to be 150-200 km (93-124 miles) in diameter and 20 km (12 miles) in depth, making it the second largest confirmed impact crater on Earth. The meteor hit near what is now the town of Chicxulub on the Yucatan Peninsula in Mexico.
When did the impact occur?
The Chicxulub impactor struck Earth around 66 million years ago, coinciding with the Cretaceous–Paleogene (K–Pg) mass extinction event that marked the end of the Mesozoic era and the reign of the non-avian dinosaurs. The impact has been conclusively dated to 66.043 ± 0.011 million years ago using radiometric dating of samples from the impact site. The meteor impact occurred at the very end of the Cretaceous period, around 66 million years ago. This coincided with a mass extinction event that wiped out approximately 75% of life on Earth, including almost all non-avian dinosaurs. The Chicxulub crater is the only known impact crater large enough to have caused such a significant extinction event.
Where exactly did it hit?
The Chicxulub crater is centered near the town of Chicxulub in Mexico, after which the crater is named. Chicxulub is located near the northwestern tip of the Yucatán Peninsula, approximately 120 km (75 miles) east of the modern city of Merida. The meteor impacted just off the coast of the Yucatan Peninsula in the Gulf of Mexico.
The crater itself lies buried underneath hundreds of meters of Cenozoic sediment. The ancient coastline at the time of impact was much closer to the crater center, approximately 30-50 km away. Significant deposits of ejecta material have been identified in southern Mexico, the Caribbean, and parts of Central America and North America, helping trace the impact point. The majority of the impact debris settled immediately around the crater site in the Gulf of Mexico and the Yucatan Peninsula.
How big was the asteroid?
Based on the immense size and geological effects of the Chicxulub impact crater, scientists estimate the asteroid or comet that struck Earth must have been approximately 10-15 kilometers (6-9 miles) in diameter. This is comparable in size to Manhattan Island. The Chicxulub impactor was likely a stony asteroid or comet estimated to be 10-15 km in diameter.
For comparison, the asteroid that created the well-known Barringer Crater impact crater in Arizona, which is just 1.2 km wide, was only about 50 meters (160 feet) in size. The dinosaur-killing Chicxulub impactor would have been 300 times larger in diameter and millions of times more massive than the Barringer asteroid. Anything large enough to create a 150 km wide crater would have been enormous and devastating when it collided with Earth.
How fast was the asteroid traveling?
The asteroid or comet responsible for creating the Chicxulub crater was likely traveling extremely fast, as are most objects that impact Earth from space. Scientists estimate the impactor was moving at a velocity of around 20 kilometers per second (12 miles per second) as it approached Earth.
At this speed, it would take the asteroid or comet only a couple minutes to travel the distance between the Earth and the Moon right before collision. This is approximately 20 times faster than the speediest bullets fired from high-powered rifles. The enormous kinetic energy of such a large, fast moving space rock striking the Earth would have been equivalent to over 100 trillion tons of TNT explosives.
What effects did the impact have?
The Chicxulub asteroid impact had catastrophic effects for life on Earth. The collision itself triggered massive earthquakes, tsunamis, wildfires, shockwaves, and volcanic eruptions across the planet. It left behind a crater over 150 km wide – this would have immediately vaporized all life nearby and created towering megatsunamis radiating outward.
Globally, the dust and debris kicked up into the atmosphere blocked sunlight for years, inhibiting photosynthesis and dramatically lowering Earth’s temperatures. This caused a severe impact winter effect, inhibiting plant growth and food chains. Over 75% of species went extinct in the aftermath, including non-avian dinosaurs, marine reptiles, and pterosaurs. Mammals and avian dinosaurs survived, eventually radiating and diversifying into the many new species that define the Cenozoic era. The meteor impact led to tsunamis, earthquakes, wildfires, and a severe impact winter. Approximately 75% of life on Earth perished.
How was the crater discovered?
The Chicxulub crater was not discovered and scientifically confirmed until relatively recently in modern geology. Its existence was first proposed in 1980 when geophysicists detected a large, semi-circular feature buried underground in magnetic survey data. Through the 1980s, researchers gathered more evidence and geological samples from the Yucatan Peninsula.
In 1991, further studies identified melt rock and shocked quartz that could only have formed from an impact, confirming the crater’s origins. Finally, in 2001, holes drilled into the crater allowed researchers to take core samples directly from the impact site – providing conclusive evidence and finalizing estimates of its immense size. The Chicxulub crater was discovered through magnetic surveys, rock samples, and drilled core samples, with its impact origin finally confirmed in the 1990s.
How was the extinction link made?
The theory that the Chicxulub impact was linked to the dinosaur extinction took longer to be accepted. In 1980, the same year the crater feature was first proposed, physicist Luis Alvarez and his geologist son Walter Alvarez put forward the hypothesis that a sudden asteroid or comet impact caused the mass extinction at the K-Pg boundary.
They discovered a global layer of iridium, an element rare on Earth but abundant in asteroids and comets, at rock layers representing the extinction event – evidence that supported an extraterrestrial impact. However, it took over a decade before the crater in the Yucatan was considered as the possible source. Further studies throughout the 1990s and 2000s have now conclusively demonstrated that the Chicxulub impact was the driving force behind the Cretaceous-Paleogene mass extinction. Luis and Walter Alvarez linked iridium at the K-Pg boundary to an extraterrestrial impact in 1980. Connections between Chicxulub and the mass extinction were established in the 1990s.
Who made the key discoveries?
There were many key contributors who helped discover and prove the Chicxulub impact origin and its link to mass extinction over several decades of research:
– In 1978, geophysicists Glen Penfield and Antonio Camargo first noticed gravity and magnetic anomalies in the Yucatan while surveying for oil companies. They published their findings suggesting a large buried impact crater in 1981.
– Father-son duo Luis and Walter Alvarez discovered the global iridium layer at the K-Pg boundary in 1980, proposing an extraterrestrial impact caused the dinosaur extinction.
– In 1990, geologists Alan Hildebrand and William Boynton published evidence they had gathered definitively linking the crater to the K-Pg extinction.
– Researchers like Jan Smit and Charles Officer helped provide evidence throughout the 1980s-90s that the deposits and rock samples around Chicxulub pointed to a large impact.
– The Chicxulub drilling projects in 2001, funded by NASA and NSF and led by Joanna Morgan, finally cored into the peak ring of the crater – providing conclusive proof of its origins.
Key discoverers were Glen Penfield, Antonio Camargo, Luis and Walter Alvarez, Alan Hildebrand, William Boynton, Jan Smit, Charles Officer, Joanna Morgan, and numerous other collaborating geologists, geophysicists, and paleontologists.
How was the impact date determined?
The precise date of the Chicxulub impact has been very accurately dated using radiometric dating techniques. By measuring the radioactive decay of certain isotopes within impact melt rock samples, researchers can determine when the impact occurred.
Ar-Ar dating and U-Pb dating have both been used to constrain the date of the impact to 66.043 ± 0.011 million years ago. These melt rock samples came from drilling projects that directly accessed the intact impact crater below younger sedimentary rock layers. Core samples retrieved from different boreholes have allowed scientists to verify the date.
The measured date matches incredibly well with the established date for the Cretaceous-Paleogene boundary, providing robust evidence that Chicxulub collided with Earth right as the dinosaur extinction was occurring. This rules out other possible extinction mechanisms like volcanic activity, which would precede the boundary. Radiometric dating of melt rock samples confirms the Chicxulub impact happened 66.043 ± 0.011 million years ago – coincident with the K-Pg mass extinction.
What effects did it have on lifeforms?
The Chicxulub impact and its aftermath had devastating consequences across all lifeforms on Earth at the end of the Cretaceous:
– All animals within a few hundred km of the impact would have perished immediately from the explosive force, heat, and megatsunamis. Shockwaves, fires, and earthquakes would have killed much further away.
– Photosynthetic marine algae and land plants had drastic reductions in productivity and diversity from the impact winter – effects cascaded up food chains.
– Plankton populations crashed, eliminating the base of the open ocean food web and causing the extinction of giant marine reptiles like mosasaurs, plesiosaurs, and ichthyosaurs.
– On land, the global climate changes and reduced plant abundance led to the extinction of non-avian dinosaurs, pterosaurs, ammonites, and many groups of mammals.
– Birds and small mammals were among the survivors, likely due to being able to subsist on seeds, carrion, and insects through the impact aftermath. Both groups radiated extensively into vacant ecological niches.
Different groups had varying rates of extinction according to their ecological roles, but overall approximately 75% of species on Earth died out.
What was the eventual ecological recovery like?
In the millions of years after the Cretaceous extinction event, global biodiversity slowly recovered as new species evolved and filled empty niches. The patterns of recovery included:
– Plant communities began to re-establish within years or decades after the impact, but took around 10 million years to fully recover former diversity.
– Plankton rebounded rapidly, as their high reproductive rates allow quick population recovery.
– Ammonites and marine reptiles never recovered. The ecological niches they formerly occupied were taken over by new bony fish and marine mammal species.
– On land, mammal and bird groups that survived the extinction rapidly evolved and diversified to exploit newly vacant niches previously held by dinosaurs.
– The rise of mammals culminated in the Eocene (~55-35 million years ago), when mammals reached their peak diversity on land prior to human impacts.
It took around 10 million years for global biodiversity to approximate Cretaceous-level diversity again. However, the reshuffled ecosystems looked very different, dominated by new mammal and bird types adapted to the post-extinction environment.
What modern animals can trace their lineage to the survivors?
Many diverse modern animal groups trace their evolutionary origins to lineages that managed to endure the mass extinction:
– Birds diversified tremendously after the extinction of pterosaurs and feathered dinosaurs. All ~10,000 modern bird species descended from the few small bird types that made it through.
– Placentals and marsupials, the two main mammal groups, radiated from small shrew-like mammal species present at the end of the Cretaceous. Humans are placental mammals.
– Snakes, turtles, crocodilians, and lizards were groups of reptiles with enough diversity to persist past the extinction. Modern species trace back to these survivors.
– The oldest known placoderm ancestors to modern bony fishes are found just after the K-Pg boundary, suggesting ray-finned fishes dominated the post-extinction seas.
Nearly all modern vertebrates are descendants of lineages that survived the mass extinction, though invertebrate groups trace further back.
The Chicxulub impact in the Yucatan Peninsula was one of the most significant events in Earth’s history, causing the Cretaceous mass extinction that reshaped global biodiversity and allowing mammals and eventually humans to become dominant. Precisely dating the 66-million-year-old impact has provided conclusive evidence that it directly caused the extinction of non-avian dinosaurs and many other species. Chicxulub left behind a 110 mile wide impact crater and a worldwide layer of iridium in the rocks, signaling an abrupt end to the Mesozoic era.