Astronomy:Chicxulub impactor

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Short description: Asteroid implicated in the extinction of the non-avian dinosaurs
See also: Chicxulub crater

[ ⚑ ] 21°24′N 89°31′W / 21.4°N 89.517°W / 21.4; -89.517

Gravity anomaly map of the Chicxulub crater area. Red and yellow are gravity highs, green and blue are gravity lows, white dots indicate sinkholes, or "cenotes", and the white line is the coastline of the Yucatán Peninsula.[1][2]

The Chicxulub impactor (/ˈtʃiːkʃəluːb/ CHEEK-shə-loob), also known as the K/Pg impactor or (more speculatively) as the Chicxulub asteroid, was the asteroid or other celestial body that struck Earth about 66 million years ago, creating the Chicxulub crater and, according to scientific consensus, acting as the main cause of the Cretaceous–Paleogene extinction event. The impactor is typically estimated to have been an asteroid with a diameter of about 15 km (10 mi), but its composition and size remain a topic of debate among experts. It is named after the town of Chicxulub Pueblo, which is near the center of the crater its impact created.

Connection with the Cretaceous–Paleogene extinctions

In the geologic record, the Chicxulub impact closely coincides with the Cretaceous–Paleogene boundary (K–Pg boundary) and the Cretaceous–Paleogene extinction event, in which most large plants[3] and nearly all large animals, including all non-avian dinosaurs, died out. The K–Pg boundary and the Chicxulub impact both date to slightly over 66 Ma[4] (though older texts often use a date of 65 Ma). Scientific consensus holds that the Chicxulub impact was the primary cause of the mass extinction. This theory is based on several lines of evidence, including the alignment in time of the impact with the mass extinction in the fossil record, the iridium anomaly in the K–Pg layer, and the extremely severe global effects of the impact, which can be found in the geologic record or estimated from models.[5]

Other proposed causes for the mass extinction include the climate effects of the Deccan Traps volcanism,[6] but most experts think that those effects were, at most, contributing factors.

The impactor

As of 2021, experts hold a range of views about the origin and composition of the impactor and physical parameters such as its size, mass, and velocity. Debates are based on the fossil record, geological analysis of the impact crater and the K–Pg boundary layer, computational fluid dynamics models, statistical studies of asteroid populations, and other sources of evidence.

In texts for a general audience, the diameter of the impactor is sometimes given as about 10 to 15 km. This is within the range of sizes considered plausible in current research, but it is toward the smaller end. In one analysis of models, by Hector Javier Durand-Manterola and Guadalupe Cordero-Tercero in 2014,[7] the median of the models' lower diameter estimates was 10.7 km, and the median of the upper estimates was 31.6 km (representing a porous comet).

One example of recent parameter estimates is in a 2020 study by Gareth Collins, Narissa Patel, et al. in Nature Communications,[8] informed by data from crater core samples (taken by IODP-ICDP Expedition 364 in 2016). The authors simulate one scenario using an impactor that is 17 km in diameter, with a density of 2,650 kg/m3 and therefore a mass of about 6.82×1015 kg, striking Earth at 12 km/s with an angle of 60⁰ from horizontal. In another scenario that also approximately matches the evidence they analyzed, they simulate an impactor that is 21 km in diameter, with a mass of 1.28×1016 kg, a speed of 20 km/s, and an impact angle of 45⁰. These values are not definitive; they merely illustrate one set of experts' estimates based on current evidence. Their density parameter approximates that of a carbonaceous chondrite asteroid, which is often considered the likely type of the impactor.[9][10][11]

It is possible, but not part of the consensus, that other related impactors hit Earth at the same time as the Chicxulub impactor, or during a period of increased impacts. The Shiva crater and the Silverpit crater have been put forward in multiple impact hypotheses, but neither of them is widely accepted as an impact crater at all. Boltysh crater is an accepted impact crater, and dates to about the same time as the one at Chicxulub, but thus far no evidence specifically connects Boltysh to either the Chicxulub crater or to the mass extinction. Research on the Cretaceous–Paleogene boundary typically assumes a single major impact, at Chicxulub.

Parent body

The question of the impactor's composition and astronomical origin (which are closely related) has been actively debated essentially since the introduction of the Alvarez hypothesis. The violence of the impact transformed, spread, and mixed the actual material of the impactor, making its composition much harder to determine than in investigations of impacts where unambiguous, intact meteorite fragments can be examined. As of 2021, there is no scientific consensus on the composition of the Chicxulub impactor, but some possibilities are considered more likely than others. Geological evidence is generally taken to suggest a carbonaceous chondrite asteroid, of which a small fragment may have been found,[11] but there is a minority view that the impactor was a comet.[12][13] Several theories have been proposed for its origin based on observations of asteroids (or comets) in the Solar System.

One theory of the impactor's origin was proposed by William F. Bottke, David Vokrouhlický, and David Nesvorný in an article published in Nature in 2007.[14] They argued that a collision in the asteroid belt about 160 Ma resulted in the Baptistina family of asteroids, the largest surviving member of which is 298 Baptistina. They proposed that the Chicxulub impactor was an asteroid member of this group, referring to the large amount of carbonaceous material present in microscopic fragments at the site, suggesting that it was a member of a rare class of asteroids called carbonaceous chondrites, like Baptistina. However, in 2011, data from the Wide-field Infrared Survey Explorer revised the date of the collision which created the Baptistina family to about 80 Ma, casting doubt on the hypothesis, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.[15]

Other work has associated the asteroid P/2010 A2, a member of the Flora family of asteroids, as a possible remnant cohort of the Chicxulub impactor.[16]

In February 2021, Amir Siraj and Avi Loeb published an article in Scientific Reports arguing for an orbitally perturbed sungrazing comet as the origin of the impactor,[13] but the theory was met with skepticism by other experts.[12]

The impact

According to Collins, Patel, et al.'s 2020 paper, A steeply-inclined trajectory for the Chicxulub impact,[8] the impactor approached from the northeast at an angle between about 45° and 60° off horizontal. It struck in a shallow ocean and, within 20 seconds of touchdown, opened a transient cavity about 30 km deep (most of the way through Earth's crust to its mantle). Although the underlying physics has many important differences, as a first approximation the impact could be visualized as a splash-like process. The transient cavity opened by the initial compression of the impactor collapsed (closed) within 180 seconds (3 minutes) and created a peak about 10 km high, which then fell and left the crater site relatively level 300 seconds (5 minutes) after touchdown.[8] Meanwhile, the impact had kicked up an ejecta curtain of debris that passed around the world at speeds of several km/s, forming the K–Pg layer found in the geological record globally.[17]

As with any other hypervelocity impact, some of the impactor and some of the target material (Earth's crust) must have vaporized into an extremely hot, bright fireball,[18] which, at the scale of the Chicxulub impact, would have radiated vast amounts of energy. (The closest comparison in human experience is a nuclear explosion, but the energy release of the Chicxulub impact was on the order of 100 million megatons,[19] while the largest bomb ever tested yielded about 50 megatons.) This flash, as well as supersonic winds[19] and extremely violent earthquakes (larger than any that can be generated by Earth's crust alone[20][21]), would have killed virtually all life within about 1,000 km, even before flying debris from the impact arrived.[19]

Debate over scale of fires

When debris did fall around the world, it would have been heated by ram pressure as it re-entered the atmosphere, becoming essentially meteors. The character and effects of this very hot re-entering debris are a topic of ongoing debate. A relatively consistent feature of the K–Pg layer is soot, implying a very large amount of combustion. This has been interpreted as the trace of an intense, global wildfire due to vegetation drying and catching fire from the radiant heat of re-entering debris in the first hours after impact. See, for example, Douglas Robertson et al.'s 2013 paper, K‐Pg extinction: Reevaluation of the heat‐fire hypothesis.[22] An alternate view is that the soot is better explained by the impactor striking an area rich in subterranean hydrocarbons (for example, kerogen, a precursor to the type of oil that humans now extract for fuel) and allowing it to burn. As examples of positions on that side of the debate, see Joanna Morgan et al., Revisiting wildfires at the K-Pg boundary, in 2013,[23] or Kunio Kaiho and Naga Oshima's Site of asteroid impact changed the history of life on Earth: the low probability of mass extinction, in 2017.[24] These latter theories give less importance to the radiant heat of the debris rain.

Longer-term effects

Main page: Earth:Cretaceous–Paleogene extinction event

Although the effects of the impact within the first few hours were extremely dramatic and violent,[19] and many individual plants and animals would have died, the majority of the mass extinction, which is defined by large numbers of entire species dying out, is usually understood as the result of changes to the planetary ecosystem on a longer timescale of months to decades or even much longer.[25] The general model is that dust and gases in the atmosphere substantially darkened irradiance at the surface (in other words, dimming the sun), which sharply lowered global temperatures and slowed primary productivity, causing a bottom-up trophic cascade of die-offs.[26] Some elaborations of this model include important roles for sulfate aerosols produced by the impact striking gypsum-rich rock, which can be modeled to produce a temporary mean air temperature drop of about 8 to 15 ⁰C in the year-to-decade range,[27] and a focus on ocean acidification as a key factor in the slow recovery of the planetary ecosystem.[25]

See also

References

  1. ↑ Nicholas M. Short, Sr., Crater Morphology Some Characteristic Impact Structures at nasa.gov, accessed January 2013
  2. ↑ The article by Nicholas M. Short, Sr. appears to have moved, but the image above does not appear to have moved with it. See Crater Morphology Some Characteristic Impact Structures at fas.org, Accessed December 9, 2015.
  3. ↑ Vajda, Vivi; Bercovici, Antoine (2014). "The global vegetation pattern across the Cretaceous–Paleogene mass extinction interval: A template for other extinction events". Global and Planetary Change 122: 29–49. doi:10.1016/j.gloplacha.2014.07.014. ISSN 09218181. Bibcode: 2014GPC...122...29V. 
  4. ↑ Renne, P. R.; Deino, A. L.; Hilgen, F. J.; Kuiper, K. F.; Mark, D. F.; Mitchell, W. S.; Morgan, L. E.; Mundil, R. et al. (2013-02-07). "Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary". Science (American Association for the Advancement of Science (AAAS)) 339 (6120): 684–687. doi:10.1126/science.1230492. ISSN 0036-8075. PMID 23393261. Bibcode: 2013Sci...339..684R.  closed access
  5. ↑ Schulte, P.; Alegret, L.; Arenillas, I.; Arz, J. A.; Barton, P. J.; Bown, P. R.; Bralower, T. J.; Christeson, G. L. et al. (2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary". Science 327 (5970): 1214–1218. doi:10.1126/science.1177265. ISSN 0036-8075. PMID 20203042. Bibcode: 2010Sci...327.1214S. https://lirias.kuleuven.be/handle/123456789/264213. 
  6. ↑ Hull, Pincelli M.; Bornemann, André; Penman, Donald E.; Henehan, Michael J.; Norris, Richard D.; Wilson, Paul A.; Blum, Peter; Alegret, Laia et al. (2020). "On impact and volcanism across the Cretaceous-Paleogene boundary". Science 367 (6475): 266–272. doi:10.1126/science.aay5055. ISSN 0036-8075. PMID 31949074. Bibcode: 2020Sci...367..266H. 
  7. ↑ Durand-Manterola, H. J.; Cordero-Tercero, G. (2014). "Assessments of the energy, mass and size of the Chicxulub Impactor". arXiv:1403.6391 [astro-ph.EP].
  8. ↑ 8.0 8.1 8.2 Collins, G. S.; Patel, N.; Davison, T. M.; Rae, A. S. P.; Morgan, J. V.; Gulick, S. P. S. (2020). "A steeply-inclined trajectory for the Chicxulub impact". Nature Communications 11 (1): 1480. doi:10.1038/s41467-020-15269-x. ISSN 2041-1723. PMID 32457325. Bibcode: 2020NatCo..11.1480C. 
  9. ↑ Goderis, S.; Tagle, R.; Belza, J.; Smit, J.; Montanari, A.; Vanhaecke, F.; Erzinger, J.; Claeys, Ph. (2013). "Reevaluation of siderophile element abundances and ratios across the Cretaceous–Paleogene (K–Pg) boundary: Implications for the nature of the projectile". Geochimica et Cosmochimica Acta 120: 417–446. doi:10.1016/j.gca.2013.06.010. ISSN 00167037. Bibcode: 2013GeCoA.120..417G. 
  10. ↑ Shukolyukov, A. (1998). "Isotopic Evidence for the Cretaceous-Tertiary Impactor and Its Type". Science 282 (5390): 927–930. doi:10.1126/science.282.5390.927. Bibcode: 1998Sci...282..927S. 
  11. ↑ 11.0 11.1 Kyte, Frank T. (1998). "A meteorite from the Cretaceous/Tertiary boundary". Nature 396 (6708): 237–239. doi:10.1038/24322. ISSN 0028-0836. Bibcode: 1998Natur.396..237K. 
  12. ↑ 12.0 12.1 Ferreira, Becky (2021-02-15). "Where Did the Dinosaur-Killing Impactor Come From?" (in en-US). The New York Times. ISSN 0362-4331. https://www.nytimes.com/2021/02/15/science/dinosaur-extinction-kt-comet-asteroid.html. 
  13. ↑ 13.0 13.1 Siraj, Amir; Loeb, Abraham (2021-02-15). "Breakup of a long-period comet as the origin of the dinosaur extinction". Nature 11 (1): 3803. doi:10.1038/s41598-021-82320-2. PMID 33589634. Bibcode: 2021NatSR..11.3803S. 
  14. ↑ Bottke, William F.; Vokrouhlický, David; Nesvorný, David (2007). "An asteroid breakup 160 Myr ago as the probable source of the K/T impactor". Nature 449 (7158): 48–53. doi:10.1038/nature06070. ISSN 0028-0836. PMID 17805288. Bibcode: 2007Natur.449...48B. 
  15. ↑ Tammy Plotner, Did Asteroid Baptistina Kill the Dinosaurs? Think other WISE... in Universe Today (2011) at universetoday.com
  16. ↑ "Smashed asteroids may be related to dinosaur killer" Reuters, February 2, 2010
  17. ↑ Artemieva, Natalia; Morgan, Joanna (2020). "Global K‐Pg Layer Deposited From a Dust Cloud". Geophysical Research Letters 47 (6): e86562. doi:10.1029/2019GL086562. ISSN 0094-8276. Bibcode: 2020GeoRL..4786562A.  closed access
  18. ↑ COLLINS, Gareth S.; MELOSH, H. Jay; MARCUS, Robert A. (2005). "Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth". Meteoritics & Planetary Science 40 (6): 817–840. doi:10.1111/j.1945-5100.2005.tb00157.x. ISSN 10869379. Bibcode: 2005M&PS...40..817C.  open access
  19. ↑ 19.0 19.1 19.2 19.3 "Chicxulub Impact Event" (in en-US). https://www.lpi.usra.edu/science/kring/Chicxulub/regional-effects/. 
  20. ↑ "Can "MegaQuakes" really happen? Like a magnitude 10 or larger?". https://www.usgs.gov/faqs/can-megaquakes-really-happen-a-magnitude-10-or-larger?qt-news_science_products=0#qt-news_science_products. 
  21. ↑ DePalma, Robert A.; Smit, Jan; Burnham, David A.; Kuiper, Klaudia; Manning, Phillip L.; Oleinik, Anton; Larson, Peter; Maurrasse, Florentin J. et al. (2019-04-01). "A seismically induced onshore surge deposit at the KPg boundary, North Dakota". Proceedings of the National Academy of Sciences 116 (17): 8190–8199. doi:10.1073/pnas.1817407116. ISSN 0027-8424. PMID 30936306. Bibcode: 2019PNAS..116.8190D.  open access
  22. ↑ Robertson, Douglas S.; Lewis, William M.; Sheehan, Peter M.; Toon, Owen B. (2013). "K‐Pg extinction: Reevaluation of the heat‐fire hypothesis". Journal of Geophysical Research: Biogeosciences (American Geophysical Union (AGU)) 118 (1): 329–336. doi:10.1002/jgrg.20018. ISSN 2169-8953. Bibcode: 2013JGRG..118..329R.  open access
  23. ↑ Morgan, Joanna; Artemieva, Natalia; Goldin, Tamara (2013). "Revisiting wildfires at the K-Pg boundary". Journal of Geophysical Research: Biogeosciences 118 (4): 1508–1520. doi:10.1002/2013JG002428. ISSN 21698953. Bibcode: 2013JGRG..118.1508M.  open access
  24. ↑ Kaiho, Kunio; Oshima, Naga (2017). "Site of asteroid impact changed the history of life on Earth: the low probability of mass extinction". Scientific Reports 7 (1): 14855. doi:10.1038/s41598-017-14199-x. ISSN 2045-2322. PMID 29123110. Bibcode: 2017NatSR...714855K. 
  25. ↑ 25.0 25.1 Henehan, Michael J.; Ridgwell, Andy; Thomas, Ellen; Zhang, Shuang; Alegret, Laia; Schmidt, Daniela N.; Rae, James W. B.; Witts, James D. et al. (2019). "Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact". Proceedings of the National Academy of Sciences 116 (45): 22500–22504. doi:10.1073/pnas.1905989116. ISSN 0027-8424. PMID 31636204. Bibcode: 2019PNAS..11622500H. 
  26. ↑ Mitchell, Jonathan S.; Roopnarine, Peter D.; Angielczyk, Kenneth D. (2012-11-13). "Late Cretaceous restructuring of terrestrial communities facilitated the end-Cretaceous mass extinction in North America". Proceedings of the National Academy of Sciences of the United States of America 109 (46): 18857–18861. doi:10.1073/pnas.1202196109. PMID 23112149. Bibcode: 2012PNAS..10918857M.  open access
  27. ↑ Brugger, Julia; Feulner, Georg; Petri, Stefan (2017). "Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous". Geophysical Research Letters 44 (1): 419–427. doi:10.1002/2016GL072241. ISSN 00948276. Bibcode: 2017GeoRL..44..419B. 

Further reading




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