The asteroid hypothesis alone is not sufficient to explain the dinosaur extinction and other animals. Many different factors influenced their disappearance to varying degrees. Many hypotheses about the extinction of dinosaurs try to explain this. Asteroids have repeatedly collided with Earth throughout its history, leaving well-defined craters. Some of these craters significantly exceed the size of Chicxulub. The volcanic activity of the Deccan Traps also played a role.
The time of the meteorite impact does not coincide with the dinosaur extinction
American geophysicist Gerta Keller from Princeton conducted years of research based on the study of microorganism traces and climate changes. The results convincingly show that the formation time of the Chicxulub crater does not coincide with the time of the dinosaur extinction. The meteorite fell 300,000 years before the disappearance of these reptiles and the end of the Cretaceous period. In 1988, Gerta Keller reported her findings from studying foraminifera in the Brazos region of Texas and El Kef, in Tunisia. She discovered that 35–40% of foraminifera disappeared 300–400 thousand years before the K/T boundary. The scientist claimed that this excludes the possibility that they were victims of a catastrophic mass extinction.
In 1990, Keller and Barrera published their subsequent research, also indicating that significant foraminifer’s extinctions occurred hundreds of thousands of years before the Cretaceous-Tertiary boundary.
In 1991, G.A. Izett and others conducted radiometric dating (40Ar/39Ar) of glass spherules at the K/T boundary in Haiti and Central America, which were 64.5 million years old. Their chemical composition matches that of the melted rocks from Chicxulub. They also discovered that the age of feldspar at the K/T boundary in the Hell Creek Formation is 64.6 million years. The discrepancy is 100,000 years.1
The asteroid fell before the end of the Cretaceous
The Chicxulub crater is hidden under later deposits. The study of these sedimentary layers, which are 9 meters thick, showed that they also belong to the Cretaceous period. Their formation took at least 300,000 years. The layers below and above the crater contain 52 species of fossils of the same animals. The same species that lived here before the explosion resettled the crater area after its fall. None of these organisms became extinct, although they lived right at the site of the asteroid fall. Moreover, this indicates that the asteroid fall did not occur at the very end of the Cretaceous. The sedimentary layers formed above the crater less than 6 years after the asteroid fall already contain traces of crawling and burrowing.
Further, Keller and her Swiss colleague Thierry Adatte studied the deposits found in the area of the small Mexican town of El Penon in the municipality of Temascaltepec, located west of Mexico City. Keller and Adatte found under El Penon a huge layer of marine sedimentary rocks from the Cretaceous period. This layer of “iridium” spherules (tiny spheres) lies at a depth of 4 to 9 meters below the iridium anomaly at the boundary of the Cretaceous and Paleogene.
Calculations, considering the rate of sediment accumulation, show that the Chicxulub asteroid impact occurred 200–300 thousand years before the end of the Cretaceous period and the mass extinction. These sediments could not have arisen as a result of any redeposition due to an earthquake or tsunami. They have an intact structure and contain evidence of slow and calm sedimentation, for example, traces of burrows dug by inhabitants of the seabed and erosional processes.
The structure of the Earth’s crust is almost unchanged
Catastrophists claim that the impact created a crater with a depth of 17–20 km. Considering that the thickness of the Earth’s crust at the impact site is about 33 km, the asteroid would have penetrated 60% of the Earth’s crust. This should have caused fractures and magma eruptions on the surface, which in turn would have completely obliterated any traces of the crater. However, since the crater still exists, the assumption of its immense depth (almost twice as deep as the Mariana Trench) is false. The tendency to constantly exaggerate all phenomena related to Chicxulub has misled once again. In reality, impact-origin structures lie superficially, diminishing in depth.
In another recent study of the crater, scientists applied much more advanced and precise seismic measurement techniques. Sean Gulick, a researcher from the Institute of Geophysics at Texas University who led the study, acknowledges that the structure of the near-surface layers of the Earth’s crust in the impact zone has hardly changed. It turned out that the underground processes preceding the asteroid impact largely shaped the modern structure of these geological formations. According to Gulick, the new data also suggest a greater depth to the seafloor where the celestial body struck than previously believed. This self-damping effect significantly reduced the impact’s energy, preventing it from even destroying deeper subsurface structures.
Numerous large asteroid impacts have occurred throughout Earth’s history
There are several well-dated meteorite craters of similar and even larger diameter than the supposed main contender for the role of the cause of the dinosaur extinction—crater Chicxulub on the Yucatan Peninsula. However, nothing catastrophic happened to Earth’s biosphere during these impact events. If asteroid impacts were responsible for extinctions, global mass extinctions would occur every 10–15 million years (given the sufficient number of craters), but such catastrophic events are not evident in Earth’s record.
Furthermore, if the sole cause of Earth’s biota crises were asteroid impacts, these crises would be relatively short-lived, which is not supported by the data. The destructive consequences of impact events could last no more than 2–24 months. Additionally, there is no evidence of any specific mechanisms of destruction that could account for these catastrophic outcomes.
By 2018, researchers had verified 190 impact craters.
Large Known Impact Craters
Vredefort. Free State, South Africa. Diameter: 250–300 km, age: 2.023 billion years (possibly 1.850 billion years) (Paleoproterozoic Era, Orosirian), Chondrite. It is the largest verified crater on Earth. The bolide was 20–25 km in size. (Allen et al., 2022)
The Sudbury impact crater in Ontario, Canada. Sudbury is an elliptical structure. Data for the map comes from a digital elevation model acquired by the Shuttle Radar Topography Mission (SRTM).
Sudbury. Ontario, Canada. Damage diameter: 260 km, ring diameter: 130 km, age: 1.85 billion years, end of the Paleoproterozoic, Statherian Period. The bolide could have been 10–15 km in size. Debris from the impact was scattered over a distance of more than 800 km. Scientists compared the mass of impact melt at two sites: 18,000 cubic kilometers at Chicxulub and 31,000 cubic kilometers at Sudbury. Most of the original Sudbury crater has been deformed and destroyed. The crater is very rich in nickel due to the fallen asteroid.
Airborne radar image of land elevation in East Antarctica. The location of the Wilkes Land crater is circled (above center). An inset of the Chicxulub crater is included for comparison. ©Ohio State University
Wilkes Land crater. East Antarctica. Basin width: 243–480 km. The ice completely buried the crater. The asteroid body was 4–5 times larger than Chicxulub. Its size could have been up to 45 km. Age: less than 500 million years. Until recently, this structure remained unverified, but recent studies confirm the impact origin of the crater. The separation of East Antarctica from southern Australia may have a connection to this event. (Klokočník et al., 2018)
Alamo bolide impact. Nevada, United States. Diameter: 100 km, age: 367–378 million years. The asteroid struck shallow marine waters in what is now southeastern Nevada. The impact occurred on the front of a reef where carbonates were accumulating in the shallow sea.
Acraman. South Australia. Crater diameter: 90 km, age: 590 million years, Ediacaran. The diameter of the chondrite was 4 km. The total area of disturbed rocks might have been as wide as 150 kilometers. At the time of impact, this area was a shallow sea.
Yarrabubba. Western Australia. Diameter: 70 km, age: ~ 2229 million years. Paleoproterozoic. This is likely the oldest recognized impact trace on Earth. The crater is heavily eroded, making parameter determination difficult.
Beaverhead. Montana–Idaho, USA. Diameter: 60 km, age around 600 million years, Neoproterozoic. Beaverhead has no visible ring structure, as tectonic activity during the formation of the Rocky Mountains destroyed it.
Charlevoix. Quebec, Canada. Diameter: 54 km, age: 342 million years (or possibly 450 million years). The asteroid was a stony one, at least 2 km in size.
Siljan. Sweden, Dalarna. Diameter: 52 km, age: 377 million years, Late Devonian.
Kara-Kul. Tajikistan. Diameter: 52 km, age less than 5 million years, Pliocene. Located at an altitude of 6,000 meters above sea level.
Montagnais. Nova Scotia, Canada. Diameter: 45 km, age: 50.50 million years, Eocene. Located on the continental shelf and buried beneath marine sediments.
Landsat image of the Woodleigh region, showing the lack of surface expression of the Woodleigh impact structure. The diameter of the Woodleigh impact structure within the Gascoyne Platform, on the Southern Carnarvon Basin in Western Australia, is estimated at 120 km from gravity and magnetic data, making it the largest impact structure discovered on the Australian continent.
Woodleigh. Western Australia, east of Shark Bay. Its diameter is not precisely determined, presumably 120 km (Iasky et al., 2001), age: 364 million years, Late Devonian. The asteroid’s size was 6–12 km.
Clearwater. Quebec, Canada. Two impact craters are located nearby. Diameters: 36 and 26 km, ages: 286.2 million years (Clearwater West) and 460 million years (Clearwater East), Early Permian and Early Late Ordovician.
As we can see, the Sudbury and Vredefort craters are significantly larger than Chicxulub. However, their impact times do not correspond to any major climatic catastrophes—no temperature drops, no changes in atmospheric composition, nothing at all. Additionally, researchers have not found any iridium layers.
Mesozoic Large Asteroids
In addition to the previously mentioned impacts, there were 12 well-studied large asteroid impacts during the Mesozoic era, the age of the dinosaurs.
Arganaty. Almaty region, Kazakhstan. Crater diameter: 300–315 km, age: 250 million years. Petrographic studies of slits from quartz veins in the rock of the basal rim confirmed the cosmogenic nature of the crater. This dates to the end of the Early Triassic (Olenekian). The crater is twice the size of the one in Yucatán. If we believe the destructive power attributed to the Chicxulub asteroid, this impact should have wiped out all life on Earth. However, no changes occurred in Earth’s biosphere.
Morokweng. South Africa. Age: 145 million years, beginning of the Early Cretaceous. LL-chondrite. Researchers had previously believed that the 70-kilometer-diameter crater was formed by a stony asteroid 5–10 km in size. New studies suggest that Morokweng is a multi-ring crater with a final rim of approximately 190 km and an outer ring of approximately 260 km. Only the central uplift has a diameter of 89 km. (Andreoli et al., 2008)
Manicouagan. Quebec, Canada. Also known as the “Eye of Quebec.” Diameter: 85–100 km, age: 215.4 million years, Late Triassic, Norian age. Scientists once linked Manicouagan to the Triassic-Jurassic extinction, but it impacted 14 million years earlier. It had no long-term effects on Earth’s flora and fauna. The bolide size was about 5 km.
Puchezh-Katunki. Nizhny Novgorod Oblast, Russia. Diameter: 80 km, Age: 167–175 million years, Middle Jurassic (Bathonian), with other estimates suggesting 195 million years. There are no significant consequences.
Kara. Nenetsia, Yugorsky Peninsula, Russia. Diameter: 65 km (initially, before erosion, it reached 120 km), age: 70.3 million years, Late Cretaceous, Maastrichtian age. Chondrite.
Tookoonooka. South West Queensland, Australia. Diameter: 55–66 km, age: 128 million years, Early Cretaceous, Barremian age.
Araguainha. Central Brazil. Diameter: 40 km, age: 244.4–254.7 million years, Early Triassic. Formed in a shallow sea area.
Mjølnir. Norway. Barents Sea, between mainland Norway and Svalbard, near Bear Island. Diameter: 40 km, age: 142 million years, beginning of the Early Cretaceous. Located at a depth of 350 m and buried under a layer of sediments 50–150 m thick. The bolide size was about 2 km.
Carswell. Saskatchewan, Canada. Diameter: 39–40 km, age: 115 million years, Early Cretaceous, Aptian age.
Manson. Iowa, U.S.A. Diameter: 35–38 km, age: 74 million years, Late Cretaceous, Campanian age. Chondrite. Its traces are almost undetectable on the surface after being smoothed over by glacial activity.
If the impact of a large meteorite leads to the extinction of entire communities of living organisms, then dinosaurs should have been wiped out at the dawn of their history and multiple times.
The source of data on the size and age of impact craters is primarily the Earth Impact Database.
Incompatibility of Asteroid Size and Earth
The Chicxulub meteorite is only about 9–10 km in size, while the Earth’s diameter is 12,742 km. To visualize this, imagine your computer monitor with a resolution of 1200 pixels, either vertically or horizontally. Now picture a single pixel on that screen. That’s roughly the scale of the “dreadful” meteorite compared to the entire planet. Clearly, the impact of this tiny grain could not have global consequences. The above statement serves as a parametric refutation of the “asteroid catastrophe” rather than a scientific proof of its inadequacy. It appears here solely for easier comparison of scales.
On a planetary scale, any of these craters represents a minuscule formation, comparable to a grain of sand for a human. For the planet, the impact of a meteorite of such size would have no significant global effect, except for some atmospheric contamination, local destruction, and tsunamis.
Eltanin Asteroid
The Eltanin asteroid impact occurred in the Pacific Ocean (southeast) near the northern edge of the Bellingshausen Sea, approximately 1,500 km southwest of Chile (between South America and Antarctica). The impact site lies where the sea floor is approximately 4–5 kilometers deep. The asteroid had a diameter of 1–4 km. Its impact triggered an earthquake with a magnitude of 8.5. Sediments on the ocean floor were enriched with iridium.
German oceanographers have found intact fragments of a Eltanin meteorite in core samples at the bottom of the Pacific Ocean.
The Eltanin asteroid’s history is quite revealing. The impact results are striking—kilometer-high tsunamis propelled marine fauna far inland. At that time, peculiar burials of organisms with a mix of marine and terrestrial forms formed along the Andean coast. Additionally, freshwater lakes in Antarctica unexpectedly revealed exclusively marine diatom algae. However, there were no long-term evolutionary consequences: the traces of this brief, powerful impact are confined to a single stratigraphic zone. And no extinctions followed these catastrophic events (Kyrill Eskov).
The Shiva Depression
By dismissing Chicxulub as the cause of dinosaur extinction, Gerta Keller turned her attention to another scenario proposed by Shankar Chatterjee—a meteor with a diameter of 40 kilometers as the culprit. This meteor, according to Chatterjee, is responsible for the massive Shiva depression (600 × 450 km) on the seabed near the coast of India (west of Mumbai) at the edge of the Seychelles-India plate. Simultaneously, it triggered the Deccan Trap eruptions. Unfortunately, this depression has a near-rectangular shape and, according to geophysical data, is not an impact crater at all but a regular bottom formation. Researchers have not yet investigated its age at all. Gravitational studies in the area also negate its crater structure.2
“We have worked extensively throughout India and investigated a number of the localities where Sankar Chatterjee claims to have evidence of a large impact he calls Shiva crater…,” writes Keller along with her colleague Thierry Adatte from the University of Neuchâtel in Switzerland in 2007. “Unfortunately, we have found no evidence to support his claims. Sorry to say, this is all nonsense.” Causes unrelated to the impact of a cosmic asteroid can explain each piece of evidence that Chatterjee presents. For example, quartz lacks the characteristic features associated with high-velocity impacts, and the iridium dates to a different period altogether, unrelated to the Cretaceous-Paleogene era.
And although the organizers of the Geological Society of America conference initially approved Chatterjee’s paper, this study was not peer-reviewed in a scientific journal. Geophysicist Steve Gulick also expressed his opinion on this matter. “There’s a bunch of problems to say the least,” Gulick said about Chatterjee’s hypothesis. “There is no evidence that [Chatterjee is] presenting of it actually being a crater.” Gulick also cast doubt on the supposed dimensions of the Shiva depression.
“However, Chatterjee et al. (2006) do not provide any substantial evidence for the existence of a crater structure and certainly not for the existence of an impact structure at Shiva,” write geologists Jayanta K. Pati and Puniti Pati in the book “Earth System Processes and Disaster Management” (2013).
The Non-Cosmic Origin of Iridium
Proponents of the catastrophic hypothesis (proposed by scientists Luis and Walter Alvarez in 1980) believe that the iridium found in sedimentary rocks at the boundary between the Mesozoic and Paleogene eras has a cosmic origin. Besides iridium, other platinum-group metals have been discovered there: platinum, osmium, palladium, and gold, as well as iron oxides.
However, the distribution of iridium concentrations across the planet does not align with a single impact site like Chicxulub. At distances of thousands of kilometers from Chicxulub, similar concentrations are found in locations close to it. Approximately 15% of the examined points at the K/T boundary do not contain any signs of anomalies, while 30% do. There is no uniform distribution.
There is no evidence unequivocally proving that the iridium in the K/T boundary deposits originates from outer space. It is merely an assumption, though a more likely one than others are. This metal is present in meteorites, but in very small amounts, albeit more than in the Earth’s crust. This is because, due to its high density, iridium sank deep into the planet during the differentiation of the Earth’s primordial molten material. And the Earth’s mantle does contain a significant amount of it (0.000084%), as much as palladium (0.000089%), more than tin (0.000039%), tungsten (0.000018%), and even gold (0.0000257%).
As early as 1981, geochemist Karl Turekian, specializing in planetology, demonstrated that the osmium isotope ratios in K/T boundary rocks are typical of Earth’s crustal rocks but do not match those found in meteorites.
Iridium in Volcanic Emissions
A number of elements in volcanic materials have a concentration three times higher than in meteorites. It is natural to assume that iridium was scattered across the Earth’s surface during intense volcanic activity at the end of the Cretaceous period (e.g., the Deccan Traps). Additionally, there is a known mechanism for the deposition of platinum-group elements (including iridium) in seawater. Meanwhile, known meteorite craters do not show increased iridium content. Comets, on the other hand, are completely devoid of iridium. In other words, none of the known asteroids that have fallen to Earth has brought a significant amount of iridium. So why attribute it to Chicxulub if there is no evidence to support this claim?
Felitsyn and Vaganov (1988) discovered high levels of iridium in volcanic emissions from Kamchatka. This provided evidence that terrestrial geological processes can leave behind high levels of iridium in rocks without the need for an impact event to explain them.3
Similarly, Christian Koeberl from the University of Vienna reported the presence of high levels of iridium in volcanic dust under the Antarctic ice. This indicated that terrestrial geological processes could leave high levels of iridium in rock deposits without any asteroid impact.
Iridium Deposits Not Linked to Mass Extinctions
Koeberl also investigated rock samples taken from the depths of the Carnic Alps in southern Austria and the western Dolomite Alps in northeastern Italy. These deposits are associated with the Permian-Triassic extinction. There are traces of iridium in the samples, but they are very insignificant compared to those attributed to the impact of the Chicxulub asteroid.
“Our geochemical analyses of these two famous end-Permian sections in Austria and Italy reveal no tangible evidence of extraterrestrial impact,” said Koeberl. “This suggests the mass extinction must have been home-grown.”
The image shows the skeletons of tyrannosaurs partially buried in the middle of what has become a desert. ©Mark Garlick
Furthermore, several dozen anomalies containing iridium have been found in known sediments of various ages, but none of them correlates with mass extinctions or significant changes in fauna. Conversely, all efforts to find traces of asteroid impacts in deposits directly corresponding to other known mass extinctions, such as the Late Ordovician or the Permian-Triassic extinctions, have yielded no results. Such traces simply do not exist.
In a study by O.L. Savelyeva, D.P. Savelyev (2016) states: “It has been found that only the boundary between the Cretaceous and Paleogene periods shows a distinct global iridium anomaly. In other stratigraphic boundaries with an anomalous content of platinum group elements, the enrichment with iridium can be very moderate.”4
Charles Officer and Charles Drake published their critique of the impact hypothesis. They synthesized previously provided data from 15 core samples containing the Cretaceous-Tertiary boundary taken from different locations around the world, including underwater. They discovered that three samples were deposited during periods of different Earth magnetic field polarities.
This meant that the rock record of the Cretaceous-Tertiary transition had different absolute ages in different locations. Therefore, any physical similarity present in these rocks of different ages could not be the result of a single instantaneous event. They also showed that elevated concentrations of iridium are present not only at the K/T boundary but also smoothly extend over approximately 60 cm of the stratigraphic column, rather than sharply increasing in a “spike” directly at the boundary. They noted that volcanologists studying the Kilauea volcano in Hawaii found that the aerosols it emits contain levels of iridium similar to those found in meteorites.
Iridium deposits are not associated with mass extinctions, nor specifically with the dinosaur extinction.
Multiple Impact Events in Earth’s History
Some researchers have suggested that instead of a single impact, there may have been multiple impacts (of comets or meteors) over a period of years. Such an assumption should reconcile the impact hypothesis with the evidence for gradual changes in biota.
As early as 1988, Hut and others suggested that the impact at the end of the Cretaceous period might have been one of a series of closely spaced impacts that contributed to the Cretaceous-Paleogene dinosaur extinction.
Stepwise Extinction
The proposed “stepwise extinction model” (Kauffman, 1986; Hut et al., 1987) expands the timeline of mass extinction caused by extraterrestrial events to 3.5 million years or more. They hypothesized that comet streams hit the Earth’s surface at intervals, typically ranging from 1 to 3 million years. Such comet impacts lead to major global extinctions, which occur in three or four stages.
What were the patterns of mass extinction? Such a stepwise extinction model still relies on an extraterrestrial source of catastrophe. It explains mass extinction by bolide impacts, even if it occurs because of multiple impacts spaced more than 1–3 million years apart. This is a necessary modification of the single-impact scenario, resulting from the consideration of more detailed paleontological data. However, this does not align with terrestrial gradualist models regarding the ultimate cause of extinction.
Deposits Contain Multiple Layers with Evidence of Ejections
The stratigraphic distribution of iridium and impact ejecta in the Gulf of Mexico reveals two events. One of them (Chicxulub) precedes the Cretaceous-Paleogene boundary by 300,000 years. The second event, associated with the global iridium anomaly, happened either at the boundary or at 100,000 years after it (Keller, 2008).
A 5–6 cm thick layer of ferruginous clay from an iridium anomaly at the contact between the Mesozoic and Paleogene. Italy, Gubbio.
Foreze-Carlo Wezel and others reported high levels of iridium in Gubbio, both well above and below the K/T boundary. They also reported the presence of spherules above and below the boundary layer. Therefore, they concluded that the spherules could not have been formed as a result of a bolide impact. In 1986, Naslund and others also reported spherules above and below the K/T boundary in Gubbio. They calculated that the deposition of spherules took about 22 million years, and the spherules could not have been the result of a single impact event.
Distinct Events at the Cretaceous-Paleogene Boundary
Recently, while studying the Gams section in Austria, A.F. Grachev and co-authors discovered that two distinct events are clearly distinguished in the transition layer at the Cretaceous-Paleogene boundary. In the first one, there is enrichment of sediments with As, Zn, Cu, Pb, Cr, Co, Ir, V, and Ni, presumably from volcanic aerosols formed during plume volcanism. The second event, an impact, occurred 500–800 years later. The corresponding layer contains nickel spherules, lonsdalite, and awaruite. Importantly, there are higher concentrations of iridium in the layer with traces of volcanic activity, while in the layer with traces of impact, iridium concentrations decrease. The famous iridium layer appears unrelated to the Chicxulub impact (Grachev et al., 2005).
In northeastern Mexico, in the zone covering the last 300,000 years of the Maastrichtian, there are two to four layers of ejecta. These Late Maastrichtian and Early Danian (already Paleogene) sediments contain layers of altered impact glass (microtektites, microkrystites), presumably ejected from the Chicxulub crater.
The first deposits (not impact-related) are associated with the massive Deccan volcanic activity that occurred between 65.4 and 65.2 million years ago. These volcanic eruptions contributed to the decline in populations of planktonic foraminifera.
Unraveling Chronological Layers
The stratigraphically oldest layer of microtektites and microkrystites ejecta represents an impact event approximately 270,000 years before the K/T boundary. Its age is 65.27 ± 0.03 Ma, the same as the Chicxulub crater.
Localities with Cretaceous-Tertiary boundary sequences that contain vesicular altered impact glass spherules (microtektites and microkrystites).
The K/T boundary impact (65.0 Ma) marks a significant drop in primary productivity and the disappearance of all tropical and subtropical foraminifera species. Iridium anomalies worldwide characterize this particular second impact.
In the early Danian period, at five locations (Bochil, Actela, Coxquihui, Trinitaria, and Haiti), there is an iridium anomaly that is tentatively identified as a third impact event around 64.9 million years ago, about 100,000 years after the K/T boundary. Here, the iridium anomaly sits above a layer of spherules and is separated from it by a layer of marl, shale, clay, or bioclastic limestone. This event may have been responsible for the extinction of species that survived the Cretaceous period and delayed recovery after the K/T impact.
None of these impacts corresponds exactly to the K/T boundary.5
Simultaneous Fall of Several Asteroids
Saint Martin-Manicouagan-Rochechouart-Obolon’-Red Wing
Landsat-5 satellite image of Lake Saint Martin in Manitoba, Canada. Outline of the estimated outer limits of the largely sediment and water-covered ∼ 40 km-diameter impact structure according to Bannatyne and McCabe (1984).
The Saint Martin impact crater in Manitoba, Canada, has a diameter of 40 km, is 227.8 million years old, and dates back to the Late Triassic. It is possible that the Saint Martin structure may have been part of a hypothetical multiple impact event that also formed the Manicouagan crater in northern Quebec, Rochechouart crater in France, Obolon’ crater in Ukraine, and Red Wing crater in North Dakota. This clearly indicates that multiple impact events have occurred in Earth’s history before.
Boltysh-Silverpit-Nadir
Scientists have dated several impact craters close to the K/T boundary, providing compelling evidence for multiple impacts. They may have formed concurrently with Chicxulub.
A part of the Boltysh impact structure is near the village of Bovtyshka in Kivorohrads’ka oblast, Ukraine. ©Wisetus
Boltysh, Ukraine. Diameter of 24 km, central uplift with a diameter of 6 km, age of 65–88 million years, Late Cretaceous or very early Paleocene. The crater isn’t the largest, but its time of impact may coincide with the K/T boundary. According to Kelley and Gurov, 2002, its age is 65.2 Ma.
Seismic data showing the crater and its concentric ring structure. ©Phil Allen (PGL) and Simon Stewart (BP)
The Silverpit crater, with a width of 12–20 km in the North Sea off the coast of Great Britain, is estimated to be around 65 million years old (Stewart and Allen, 2002).
The Nadir crater is an underwater structure on the Guinea Plateau in the Atlantic Ocean, 400 km off the coast of Guinea. An asteroid, approximately 400 meters in size, impacted the ocean floor at a depth of around 800 meters. The crater measures 8.5 km in diameter and has a depth of about 40 meters. Researchers discovered it during seismic surveys. They believe it is an impact crater. It formed at the boundary between the Cretaceous and Paleogene periods around 66 million years ago, roughly the same time as the Chicxulub crater (Science Advances in 2022).
Popigai-Chesapeake Bay-Toms Canyon
Here are three more impacts that likely happened at the same time:
Popigai (Yakutia, Anabar uplift). Diameter: 100 km, 35.5 million years old, end of the Eocene (Priabonian). The size of the bolide is about 8 km. H chondrite. The asteroid impact transformed graphite in the ground into the hexagonal diamond modification—lonsdaleite; such was the strength of the shock pressures. However, it did not disperse this graphite into the atmosphere to cause an asteroid winter.
Chesapeake Bay. Virginia, U.S.A. Diameter: 90 km, age: 35.5 million years, end of the Eocene. Fell into the water off the coast.
Toms Canyon impact crater. Diameter: 22 km, 35.5 million years old. Formed as a result of an asteroid falling onto the Atlantic Ocean’s continental shelf, about 160 km east of Atlantic City, New Jersey.
It is noteworthy that these three impacts (most likely there were more)—Popigai, Chesapeake Bay, and the Toms Canyon crater (USA)—happened at the same time, about 36 million years ago, and were comparable in size to Chicxulub. Presumably, there were many more meteorites than just these three. Despite such intense bombardment, no global changes in the Earth’s biosphere occurred at this time. No climate change, no mass extinctions—nothing at all.
The Iridium Layer has Different Compositions in Various Locations
Cylindrical core samples recovered from wells in Yucatan. Rocks were subjected to immense heat and pressure at the time of the impact. The samples were collected in the 1990s and early 2000s during drilling projects under the International Continental Scientific Drilling Program. ©Barcroft Media
Finally, a recent study challenges Chicxulub as the source of the iridium layer at the K/T boundary worldwide. Researchers analyzed cores retrieved from the peak rings of the Chicxulub impact structure during the International Ocean Discovery Program—Expedition 364 of the International Continental Scientific Drilling Program in April–May 2016.
Chondrite normalized the PGE pattern (logarithmic scale). The PGE pattern from the upper transitional unit (red square, blue diamond, blue triangle) is different from the near chondritic PGE abundance patterns known from Stevns Klint and Caravaca. The PGE ratios are evidence that the globally distributed iridium layer is not preserved in the Chicxulub impact structure. It appears to have been different projectiles and different events in time that produced the PGE pattern in Europe and in the upper transitional unit preserved within the Chicxulub impact structure.
Chicxulub structure is considered a possible impact crater that led to the global distribution of PGE (Platinum Group Elements)-enriched deposits at the K/T boundary. However, the PGE characteristics (deposits of meteoritic matter, marl) clearly differ from the meteoritic component corresponding to the chondritic impactor. This PGE signature is significantly different from the European Cretaceous-Paleogene boundary sections of Caravaca in Spain and Stevns Klint in Denmark.
Cliff at Stevns Klint. The chalk at Steven’s Klint is considered of such importance because the boundary layer (Fiskeler) is so well-defined in a 3–12 centimeter-thick dark band devoid of other fossil debris. ©danmarksrejsen.dk
The chemical composition shows that the Cretaceous-Paleogene boundary is not associated with the Chicxulub impact. The Ni/Co ratio of Chicxulub (11) is closer to that of the Mundrabilla iron meteorite from Australia (15.5) than to that of chondritic meteorites (20). The Ru/Ir ratio in two samples from different depths of Chicxulub is 2 and 4. The iron meteorites Mundrabilla and Duchesne have Ru/Ir ratios of around 3 and 5, respectively. It appears that different impactors and different events over time created the PGE structures in Europe and the Chicxulub impact structure.
Data on the chemical composition of deposits at the K/T boundary calls into question the Chicxulub impact structure as the crater that became the source of elevated PGE content in Europe and worldwide. Thus, evidence of a continuous and widespread iridium layer is insufficiently substantiated (Gerhard Schmidt, 2023).6
The Deccan Traps Volcanism
The Late Cretaceous was generally a time of significant tectonic activity, as evidenced by, in particular, arc volcanism in the Pacific Ocean.
However, the most active volcanic activity at the K/T boundary was associated with events of continental trap magmatism on the Deccan Plateau in India. In trap eruptions, there is no volcanic cone or crater; molten basalts erupt from numerous fissures and spread over plains for tens of kilometers, filling river valleys and other natural depressions. The area of the Deccan Traps reaches, according to various estimates, from 0.5 to 1.5 million km2, and the volume of erupted lava is 2 million km3 (Vincent E. Courtillot, 1990). The cause of the traps is the rise of a large flow of hot mantle material, the Reunion hotspot, over which the Indian subcontinent was passing at that time. This hotspot near Reunion Island is still active, with the last eruption in 2007.
Trap lava eruptions could have brought significant amounts of iridium to the surface from the depths of the planet. The volcanic dust and gases released into the atmosphere at that time could have significantly worsened the environmental situation. However, trap volcanism did not become the sole cause of mass extinction, as it was a local phenomenon, not ubiquitous. Its intensity was insufficient for global climate and biosphere changes.
Location and size of exposed outcrops of Deccan Traps volcanic rocks (basalt) in India, which dates from 64 to 67 million years ago. An unknown volume of volcanic rocks also erupted offshore. The immense volume of basalt, over 600 km (373 miles) in diameter, now forms an impressive mountainous region covering a significant portion of western India. ©James Barnet
Stages of the Deccan Volcanism
This was a long, multi-stage process, intensifying and subsiding at times, lasting 8 million years—from 68 to 60 million years ago7—too stretched out in time for its negative consequences to accumulate. On the contrary, over such a long period, they were completely neutralized and had no global consequences. Furthermore, the formation of the bulk of the Deccan basalts in western India, occurring around 65 million years ago, stretched over 30,000 years and preceded the end of the Cretaceous period by half a million years. The most voluminous Deccan Traps volcanism preceded the meteorite impact but did not follow it.
The massive Deccan volcanic mountain ranges of the Western Ghats (east of Mumbai) reach up to a height of 3500 m and consist entirely of layered lava flows. (Photo courtesy of G. Keller).
Research shows that the Deccan volcanoes erupted in three main phases. The initial and smallest Phase-1 was ~ 67.4 million years ago. The main Phase-2, with ~ 80% of the total volume of the Deccan, ends below the KT boundary. The second, most powerful phase, probably began about 400,000 years before the K/Pg boundary (Robinson et al., 2009). The final phase of Phase 3 occurred in the early Danian, about 280,000 years after the mass extinction. (Courtillot & Renne, 2003; Chenet et al., 2007, 2008, 2009; Jay et al., 2009). All phases of the Deccan Traps consist of a series of smaller individual eruptions, which occurred roughly every 2,000 years (Jay et al., 2009).
Volcanic Emissions into the Atmosphere
Scientists have recorded 11 cases of significant volcanism over the past 300 million years. In addition to the outpouring of basalts, huge volumes of volcanic gases, including CO2, were released into the atmosphere. Moreover, some of these eruptions caused warming (the greenhouse effect), while others caused cooling (ash in the atmosphere).
Overall, factors increasing acidity and carbon dioxide content are not detrimental to all species indiscriminately; for some of them, they proved to be not so significant or even beneficial, including precisely due to the increase in mortality among competing individuals. Terrestrial plants even benefit from a small excess of CO2.
Modern research shows that most volcanic ash settles on the Earth’s surface within six months. Thus, volcanism also could not have been the cause of the dinosaur extinction, but it certainly contributed to this process.
Deccan Traps and Their Impact on Dinosaur Extinction
Even before the seas began to recede, the eruptions of the Deccan Traps, intensifying and weakening at times, led to additional stresses in the biosphere. Over several hundred thousand years preceding the asteroid impact, these eruptions caused significant climate disruptions (Schoene et al. 2015). The environmental changes caused by volcanoes may have affected dinosaur communities in ways such as changes in population structure or community ecology.
Analysis of the chemical composition of Indian lava rocks indicates that they originated in the Earth’s mantle, which is also rich in iridium.
Anomalously voluminous volcanic eruptions correlate significantly better in time with mass extinction events than any impacts; however, a causal relationship is not established with high certainty. Only one clear coincidence in age with a meteorite fall has been documented—the Cretaceous-Paleogene dinosaur extinction.
Attempts to Link Asteroid and Active Volcanism
Proponents of the asteroid catastrophe have tried to connect the Deccan Traps to the asteroid impact. They argue that the impact caused such a powerful earthquake on Earth that it, passing through the entire planet, focused directly on the opposite side of the Earth from the Chicxulub crater, right where India is located. This, they claim, triggered the massive lava outpourings.
Palaeogeographic reconstruction of the Earth around the time of the K/Pg mass extinction, illustrating the locations of Deccan Traps volcanism in India and asteroid impact in Mexico. Reconstruction created using the Ocean Drilling Stratigraphic Network (ODSN) Paleomap Project.
However, evidence does not support this assumption. First, at the end of the Cretaceous period, India was still continuing its northward movement and was not on the opposite side of the Earth from the impact site. Second, the Deccan Trap eruptions began before the asteroid fell and continued for a long time afterward (Blair Schoene et al., 2014). That is, there is no causal relationship between these events.
- Izett, G.A., 1991. Tektites in Cretaceous-Tertiary boundary rocks on Haiti and their bearing on the Alvarez impact extinction hypothesis. ↩︎
- Sankar Chatterjee et al., 2003, The Shiva Crater: implications for Deccan volcanism, índia-Seychelles rifting, dinosaur extinction, and petroleum entrapment at the K-T boundary ↩︎
- S. B. Felitsyn &P. A. Vaganov, 1988, Iridium in the ash of Kamchatkan volcanoes ↩︎
- Savelyeva O.L., Savelyev D.P., 2016. The origin of iridium and other platinum-group elements anomalies at different stratigraphical levels ↩︎
- G. Keller et al., 2003. Multiple impacts across the Cretaceous–Tertiary boundary. ↩︎
- Critical comment on “Globally distributed iridium layer preserved within the Chicxulub impact structure” published in Science Advances 7, eabe3647 (2021) ↩︎
- According to Venkatesan et al. 1993; Prasad et al. 1994 – 69-63 million years ago. ↩︎
