Chicxulub crater

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Coordinates: 21 ° 18 ′  N , 89 ° 36 ′  W

Map: Mexico
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Chicxulub crater​
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Mexico
The Chicxulub crater
The Chicxulub crater after measurements of the gravity anomaly . The white dots mark the location of the many cenotes that are lined up like pearls along the outer crater ring.

The Chicxulub crater (after the place Chicxulub Pueblo , by Mayathan Ch'ik Xulub [ tʃikʃuˈlub ], ch'ik "flea, tick", xulub ' "devil, demon, horn") is according to the latest dating 66 million years old impact crater with a diameter of approx. 180 km in the north of the Yucatán peninsula in North America ( Mexico ). As it is buried under thick sedimentary rocks and not eroded , it is one of the best-preserved large impact craters on earth . In the context of the Cretaceous-Paleogene boundary , it is associated with the extinction of dinosaurs and much of the Mesozoic fauna and flora during the transition to the Cenozoic .

Location, size and identification of the crater

The center of the Chicxulub crater is located on the Yucatec coast, roughly below the eponymous town of Chicxulub Pueblo , north of Mérida . While the southern part of the impact structure is in the area of ​​the state of Yucatán , its northern part extends out into the Gulf of Mexico . From the edge of the crater to its center, the thickness of the Cenozoic sediment layers deposited above increases from about 300 to 1000 meters.

The crater was detected by measuring magnetic and gravitational anomalies in 1991 and clearly identified as an impact crater. It forms an almost circular basin about 180 km in diameter with a central mountain and an inner ring structure. The determined gravitational anomalies led to the assumption that the crater has at least three rings and probably an additional outer ring with a diameter of approx. 300 km. The crater depth is 10 km (30 to 35 km immediately after the impact). Since the size ratio of an impactor to the impact crater generated is usually between 1:10 and 1:20, the diameter of the asteroid or comet at that time should have been around 10 to 15 km.

On the surface, little is noticeable of this third largest impact crater on earth , as the north of the Yucatán is very flat. However, studies have shown that slight elevations in the ground form almost semicircular structures and the strength of the tropical soil formation also traces the earlier crater. In addition, with a radius of about 83 km (diameter of 166 km) there is a concentric, string of pearls-like arrangement of the cenotes typical of this karst area . The data from the Shuttle Radar Topography Mission also show a clear semicircular topography in the area of ​​the impact structure. A 3D simulation supported by geophysical observations suggests that the Chicxulub crater was formed by an impact from the northeast, inclined horizontally at an angle of about 45-60 °.

Exploration of the Chicxulub crater

Covering the Chicxulub Impact Crater with thick younger sedimentary rocks has not only delayed its discovery, but also complicates its exploration and makes geological core drilling extremely costly.

Research history

The history of the discovery of Chicxulub crater began in the 1940s when geophysicists from the Mexican state oil company PEMEX discovered an unusual gravitational and magnetic anomaly during an airborne exploration in the Mérida area . In the hope of finding an oil deposit , several wells were carried out in the 1950s, which, although not oil, produced andesite- like rocks that are atypical for the Yucatán platform . Since most geologists were not familiar with the phenomenon of impact craters at that time, the first internationally accessible inventory by López Ramos (1975) interpreted the subsurface structure as a volcano that had penetrated the chalk sedimentary rocks . The geophysicists Penfield and Camargo first suggested at a geophysical congress in 1981 that this could be a meteorite crater . However, your idea initially met with little response.

Computer generated map of Chicxulub crater based on the gravity anomalies

In the late 1970s, a research team at the University of Berkeley led by the physicist Luis Walter Alvarez and his son, the geologist Walter Alvarez , worked on the magnetostratigraphy of marine deposits from the Upper Cretaceous and the Paleogene near the town of Gubbio in the central Italian region of Umbria . In the chalk-paleogene boundary layer , which is particularly pronounced there , the researchers found an unusually high proportion of the precious metal iridium, which is normally very rare on earth and mostly comes from volcanic sources . The significant iridium concentration within the narrow time window of the KP limit, however, almost excluded volcanic influences and led to the assumption of a large asteroid impact, which had severely polluted the terrestrial biosphere and led to a global extinction of species. The “revolutionary” hypothesis of father and son Alvarez was published in the journal Science in June 1980 and received a lively and long-lasting response in the geosciences . A ten-year and initially unsuccessful search for the postulated impact crater followed. It was discovered in 1991 after the Cretaceous-Paleogene border deposits were found to be thickest in what is now the Gulf of Mexico , and after extensive analysis of the Mexican Oil Company's decades-old records. It is an irony of this science thriller (vividly described in Walter Alvarez's book T. Rex and the Crater of Doom ) that the sample of the Yucatán andesite , on which both the detection of the impact indicators and the first age dating of the crater succeeded, were for years as Paperweight of a geologist for the oil company PEMEX.

Geophysical investigations

In order to draw conclusions about the energy released by the asteroid impact and to be able to determine the angle of impact and the size of the impactor, the dimensions and structure of the crater had to be known as precisely as possible. This required a variety of geophysical methods such as geomagnetics , gravimetry and seismics . While the first reconstruction of the Chicxulub crater was mainly based on the documents from PEMEX, further geophysical data based on land seismics was collected by the UNAM Institute for Geophysics (Mexico) in the 1990s . At the beginning of 2005, further seismic measurements were carried out on board the R / V Maurice Ewing in the Gulf of Mexico and the results were then presented at scientific conferences and in specialist literature.

Drilling

The only way to directly analyze the impactites of the Chicxulub crater is through technically complex and costly drilling. Some of the drilling projects carried out in the 1950s and 1960s reached a depth of 3,500 meters, but they are of little geological relevance, as they were designed to find oil deposits. In addition, most of the samples sporadically taken at the time are considered lost. Therefore initiated UNAM 1996, a flat-drilling program in the state of Yucatán , where due to the low depth of up to 800 meters only impactites the ejecta were recovered from outside the actual crater area. The chances of finding fragments of the impactor with a borehole are extremely slim, however, because at the moment of the impact it almost completely evaporated due to the enormous release of energy.

The so-called Chicxulub Scientific Drilling Project at Yaxcopoil, south of Mérida, was carried out in 2002 in a cooperation project under the direction of the International Continental Deep Drilling Program at the GeoForschungsZentrum Potsdam . The core hole Yaxcopoil-1 reached a depth of 1511 meters and produced an almost complete drill core of Cenozoic sedimentary rocks (0-795 m), various layers of impactites within the crater (794-896 m) and a sequence of rock layers from the Upper Cretaceous, the presumably comes from a megablock of the subsurface that slid into the crater (896–1511 m). Several research groups then examined the well-preserved impactites from several aspects. The first results were published in 2004 in a special volume in the journal Meteoritics & Planetary Science . Based on the geophysical results obtained so far, further deep drilling in the Chicxulub crater was planned for 2016. The first results of this new drilling, which reached 1335 meters below the sea floor, were presented in January 2018.

Surface rocks as impact witnesses

In the past two decades, sedimentary rocks attributed to the asteroid impact have been discovered in the near and far crater orbit. In addition to deposits, some several meters thick, in the southeastern United States, Haiti, Cuba, and northeast and central Mexico, it was above all chaotic breccias in southeast Mexico and Guatemala that attracted particular attention. An example of this are the limestone breccias discovered in southeastern Yucatán, which sometimes contain debris fragments from the interior of the crater. It is hoped that the analysis of these loose sediments found between 280 and 365 km from the crater center will provide more precise data about the Chicxulub crater as well as further knowledge with regard to the mass extinction at the time .

What all these sediments have in common is that they, like the crater rocks and the globally detectable Cretaceous-Paleogene boundary layer , belong to the so-called event deposits as short-term phenomena , as they arise within months, days, hours or even minutes after an impact. These temporal orders of magnitude lie beyond the conventional stratigraphic and radiometric resolution, but are increasingly the subject of research in a still young scientific discipline, event stratigraphy .

In 2019, an international team of researchers published a study of deposits in the Hell Creek Formation in the area of ​​the Tanis terrestrial deposit in North Dakota , USA, which the researchers said formed less than an hour after the impact. A tidal wave had piled numerous ammonites, fish (including sturgeon and paddlefish ), land animals and parts of plants on top of each other, mixed with ejecta from the impact, which was preserved both in the gills of the fossil fish and in the interior of amber .

The Chicxulub impact and mass extinction on the Cretaceous-Paleogene border

Chalk-Paleogene Boundary (dashed line) in Trinidad Lake State Park, Colorado (USA)

The timing of the Iridium anomaly with the extinction event at the KP boundary was the central point of the Alvarez study from 1980. The scenario required an impact body about 10 to 15 km in diameter, the kinetic energy of which was suddenly released and triggered a worldwide wave of destruction, which about 70 to 75 percent of all species at that time fell victim. With the Chicxulub impact as a “ global killer ” , the cause of the disappearance of the dinosaurs and many other life forms seemed to have been found.

While the majority of geoscientists essentially shared this view, others criticized in the early 2000s that the impact could not have played the role it had been ascribed for two decades. Discoveries of impact glasses in older Cretaceous deposits were interpreted as an indication that the Chicxulub crater had already formed 300,000 years before the actual Cretaceous-paleogene boundary layer and possibly belonged to a whole series of impact events. The mass extinction would therefore not be due to an asteroid, but mainly to the extensive flood basalts of the Dekkan Trapps in western India. The volcanic activities of this so-called Magmatic Great Province with considerable outgassing of carbon and sulfur dioxide in the higher gigaton range over a period of several hundred thousand years would have been sufficient to permanently destabilize the terrestrial biosphere.

This “predating” met with criticism from the start and is considered unlikely in view of the current research results. The use of the most modern dating methods with very low tolerance ranges led to the result that the impact event and the Cretaceous-Paleogene boundary coincide precisely in time. The impact winter following the impact is now considered factually secured. Until recently, there was largely agreement in science that at the end of the Cretaceous, biodiversity and the stability of ecosystems were on the decline. In the meantime, there is an increasing number of indications that the ecological situation in the late Maastrichtian was more stable than assumed for a long time and that there is little evidence of a “creeping” Dekkan-Trapp extinction before the CP border. More recent studies therefore come to the conclusion that the Chicxulub impact alone ushered in the end of the Mesozoic fauna.

The currently most probable scenario assumes that 66.040 million years ago (± 0.032 million years) a 14 km large asteroid hit a tropical shallow sea at a speed of about 20 km / s (72,000 km / h) at a relatively steep angle, detonated with the explosive power of at least 200 million Hiroshima bombs and evaporated almost completely in the process. The impactor hurled several thousand cubic kilometers of carbonate and evaporite rock over long distances as glowing ejecta into the stratosphere due to the force of the explosion, which was probably heard all over the globe . While most of the components of the hail of debris fell back to the surface, a smaller part was hurled out of the earth's gravitational field. In addition to the immediate effects of the impact such as megatsunamis , a supersonic pressure wave and heat wave, as well as earthquakes of magnitude 11 or 12, wildfires occurred around the world, the extent and duration of which is currently still being discussed. Within a few days, a large amount of soot and dust particles were distributed throughout the atmosphere, absorbing sunlight for months, causing a global cold snap and largely bringing photosynthesis of plants on land and in the oceans to a standstill. An additional cooling factor was possibly sulfuric acid aerosols , which, according to a recent study, made a decisive contribution to a drop in temperature of 26 K and ensured that the global average temperature fell below freezing point for several years .

The oceanic and mainland biotopes were equally affected by the biological crisis that followed . In the course of a period of time that cannot be precisely defined, in addition to the dinosaurs and the megafauna native to the oceans , the ammonites , almost all calciferous foraminifera and most bird species died out. After a cold phase presumably lasting several decades, rapid warming, leading to heat stress, began with a duration of around 50,000 years, due to a greater part of the billions of tons of carbon dioxide that the impact had released within seconds as a result of the evaporation of oceanic floors Massively increased CO 2 emissions from the Deccan Trap, possibly initiated by the tectonic tremors of the asteroid impact. This assumption is in accordance with the relatively new hypothesis that due to the impact energy of 3 × 10 23 joules (according to another calculation 1 × 10 24 joules) and the tectonic shock waves triggered by it, the long "smoldering" Dekkan-Trapp a considerable increase in its Activity recorded. According to the relevant studies, the geologically short-term discharge of 70 percent of all Dekkan-Trapp flood basalts, reaching over thousands of years into the Paleogene, is due to the Chicxulub impact. In science, however, there is disagreement as to whether the main activity of this Magmatic Greater Province took place immediately at or shortly after the Cretaceous-Paleogene border or already before.

The authors of a study published in 2017 indicate that the Chicxulub asteroid hit rock strata with high concentrations of hydrocarbons and sulfur . Due to the large-scale heating and evaporation of the oceanic sediments in this region, extensive amounts of soot and sulfate aerosols were distributed in the stratosphere , which significantly increased the climatic effects of the following impact winter. If the asteroid had hit an area with a lower proportion of hydrocarbons (around 87 percent of the earth's surface), the biological crisis would presumably have been less severe, with a significantly higher survival rate for the Mesozoic fauna. The probable impact angle of approximately 45 to 60 ° also suggests that the asteroid developed the greatest potential for destruction in terms of ejecta mass and evaporated sediment layers in this angle range.

The impact catastrophe not only caused a strong reduction in fauna, but also resulted in almost 60 percent of all plant species in some regions becoming extinct. Fungi, moss and lichens spread around the world, and after a while the ferns grew to a peak. Nevertheless, the regeneration of terrestrial biotopes was relatively quick compared to other mass extinctions in the past, which benefited, among other things, the mammals, which already in the early Paleocene recorded an initial increase in biodiversity and thus the formation of new species. In the oceans, the chemical composition of the near-surface water layers, including the pH value, resembled that of the late Cretaceous again after around 80,000 years, while the complete renewal of the oceans down to the deep sea areas probably took more than a million years.

literature

  • David Shonting, Cathy Ezrailson: Chicxulub - The Impact and Tsunami. Springer, Cham 2017, ISBN 978-3-319-39485-5 .
  • Walter Alvarez: T. rex and the crater of doom , Princeton University Press 1997, Princeton, New Jersey.
  • Rüdiger Vaas: Death came from space. Meteorite impacts, earth orbit cruisers and the demise of the dinosaurs . Franckh-Kosmos Verlag-GmbH & Co., Stuttgart 1995. ISBN 3-440-07005-0 .
  • Kenneth J. Hsü: The last years of the dinosaurs . Birkhäuser, Basel 1990. ISBN 3-7643-2364-7 .

Web links

Commons : Chicxulub Crater  - Album with pictures, videos and audio files

Individual evidence

  1. ↑ Victoria Bricker, A Dictionary of The Maya Language As Spoken in Hocaba, Yucatan
  2. ↑ a b Alan R. Hildebrand, Glen T. Penfield, David A. Kring, Mark Pilkington, Antonio Camargo, Stein B. Jacobsen, William V. Boynton: Chicxulub Crater: A possible Cretaceous / Tertiary boundary impact crater on the Yucatán Peninsula, Mexico . (PDF) In: Geology . 19, No. 9, September 1991, pp. 867-871. (accessed December 10, 2015)
  3. ↑ Virgil L. Sharpton, Kevin Burke, Antonio Camargo-Zanoguera, Stuart A. Hall, D. Scott Lee1, Luis E. Marín, Gerardo Suáarez-Reynoso, Juan Manuel Quezada-Muñeton, Paul D. Spudis, Jaime Urrutia-Fucugauchi: Chicxulub Multiring Impact Basin: Size and Other Characteristics Derived from Gravity Analysis . (PDF) In: Science . 261, No. 5128, September 1993, pp. 1564-1567. doi : 10.1126 / science.261.5128.1564 . (accessed December 10, 2015)
  4. ↑ Kenkmann, Thomas: With the force of millions of hydrogen bombs. Humboldt University Berlin, April 10, 2004, accessed on November 15, 2016 .
  5. ↑ Tillemans, Axel: Asteroid let the earth's mantle under Chicxulub crater shoot up one kilometer. In: Image of Science. January 3, 2002, accessed September 8, 2019 .
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  7. ↑ Pope et al., 1991; Hildebrand et al., 1995
  8. ↑ a b Gary L. Kinsland, Kevin O. Pope, Manuel Hurtado Cardador, Gordon RJ Cooper, Duncan R. Cowan, Michael Kobrick, Gary Sanchez: Topography over the Chicxulub impact crater from Shuttle Radar Topography Mission data. In Large Meteorite Impacts III . (PDF) In: Geological Society of America (GSA Paper 384) . 2005, pp. 141-146. doi : 10.1130 / 0-8137-2384-1.141 . (accessed December 10, 2015)
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  12. ↑ Swisher Swisher, José M. Grajales-Nishimura, Alessandro Montanari, Stanley V. Margolis, Philippe Claeys, Walter Alvarez, Paul Renne, Esteban Cedillo-Pardoa, Florentin JM. R. Maurrasse, Garniss H. Curtis , Jan Smit, Michael O. McWilliams: Coeval 40 Ar / 39 Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites . (PDF) In: Science . 257, No. 5072, August 1992, pp. 954-958. doi : 10.1126 / science.257.5072.954 . (accessed on December 11, 2015)
  13. ^ Researching and Mapping the Chicxulub Impact Crater , University of Texas, Austin. Retrieved June 14, 2008
  14. ^ Chicxulub Scientific Drilling Project. ( Memento of the original from June 21, 2006 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved June 14, 2008  @1@ 2Template: Webachiv / IABot / www.icdp-online.de
  15. ↑ Meteoritics & Planetary Science, Volume 39, Issue 6 ( table of contents at Ingenta Connect) ( Memento of the original from July 17, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.ingentaconnect.com
  16. ↑ Drill cores from the global disaster derstandard.at, accessed on April 7, 2016
  17. ↑ At the «Ground Zero» of the Chicxulub crater
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    Chicxulub asteroid impact: Stunning fossils record dinosaurs' demise. On: bbc.com of March 29, 2019
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  37. ↑ Kunio Kaiho, Naga Oshima: Site of asteroid impact changed the history of life on Earth: the low probability of mass extinction . In: Scientific Reports . November 7, 2017. doi : 10.1038 / s41598-017-14199-x .
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  39. ^ Gregory P. Wilson: Mammals across the K / Pg boundary in northeastern Montana, USA: dental morphology and body-size patterns reveal extinction selectivity and immigrant-fueled ecospace filling . (PDF) In: Paleobiology . 39, No. 3, May 2013, pp. 429-469. doi : 10.1666 / 12041 .