Now that the geologists and geophysicists have precisely dated the geologic events, if not their precise linkages, paleontologists, geologists, and atmospheric scientists are examining the precise effects of each and their combined effects in the geologic and fossil record.[1] Analyzing the effects of different parameters helps scientists determine the precise effects of each event and their effects on different types of animals.
The dinosaurs of the Late Cretaceous appear to have been particularly susceptible to the effects of an extinction event. All three major dinosaur groups had already been in decline.[2] They had difficulty adapting to new conditions, which is indicated by the fact that extinct species were not replaced by new species.
Volcanism and asteroid impacts can cause swings in temperature in both directions. Carbon dioxide emissions can act as a global warming gas and warm the climate. On the other hand, sulfur aerosols and possibly soot can block sunlight and cause global cooling. Julia Bruegger et al. modeled the effect of the rise in temperature prior to the impact and the fall in temperature at the coldest point just after the impact and determined that this would be extremely difficult for animals as they might have initially migrated northward to stay in a cooler climate and then the temperature would have suddenly become extremely cold.[3]
Zhang et al. studied the geologic and fossil record in Northern China.[4] They found that species diversity began to drop 66.3 Ma (prior to the asteroid impact), at the time of the initiation of Deccan Traps volcanism. They found that carbon dioxide in the atmosphere and global temperature both increased prior to the impact. Then, the temperature began to drop prior to the 66.0 impact event, possibly due to sulfur aerosols due to offgasing from Deccan Traps blocking sunlight.
Just after the impact, there was a large drop in global temperature and temporary global winter. There is controversy over whether this was the result of sulfate aerosols or soot blocking the sun. Soot at the K-Pg boundary led scientists to conclude that hot spherules from the asteroid triggered worldwide forest fires; however, Goldin and Melosh did a theoretical simulation and found that clouds of spherules would have limited the radiation reaching the earth’s surface and that the spherules would have cooled before reaching the surface. Instead of 10 kW/m2 (required for forest fire ignition), they calculatred that the energy of the spherules would have only been 5 kW/m2.[5] A lack of charcoal at K-Pg boundary and the presence of carbon cenosphores at K-Pg boundary leads some to conclude that the soot came from the impact crater.[6] Kaiho proposed that stratospheric soot from the impact blocked sunlight, dropped worldwide temperatures, left soot at the K-Pg boundary around the world, and caused the extinction.[7] Most scientists think that sulfate aerosols blocked sunlight and that acid rain caused extinctions, but Kaiho argued that acid rain did not take place to an appreciable degree since freshwater animals, such as crocodiles, survived the End Cretaceous extinction.[8]
The Hell Creek and Lance formations in North Dakota provide a record of the flora and fauna before and after the impact. Archibald and Bryant, at the Museum of Paleontology at Berkeley, counted species below and above the K-Pg boundary.[9] They found that 35 species out of 111 at Hell Creek Formation survived the End Cretaceous extinction. There were 20 species of dinosaurs, none of which survived the impact. Only one mammal species was found above the impact strata whereas 28 mammal species were in the Cretaceous. They found that 88% of land dwelling species at Hell Creek perished but only 10% of freshwater species went extinct. The Berkeley researchers found that land animals that depended on living plants perished, but the freshwater food chain began with detritus, which would have continued as a food supply after photosynthetic plants and microbes died. Brusatte et al. found that the primary factor in the extinction at Hell Creek was the asteroid impact; however, they cautioned that other formations in the world need to be studied before concluding that the impact was the primary cause of extinction around the world.[10]
An abundance of fungal spores just above the impact layer indicates that photosynthetic plants shut down and died.[11] The only animals that survived were small animals, less than 50 pounds, that consumed insects. Even though all live plants perished, insects lived off the decayed plant matter. [12] Birds and lizards that ate insects also survived.
After the Great Permian Extinction, it took tens of millions of years for plant communities to recover. Unlike the Great Permian extinction, plants recovered quickly after the End Cretaceous extinction; thus, placental mammals, birds, and lizards adapted to the new ecosystems. The first plants to recover were ferns, which can germinate on bare soil. Flowering plants seem to have adapted to the new conditions more rapidly than other types of plants after the extinction.
What effect did the End Cretaceous extinction have on sea life? The giant marine reptiles, which needed to surface to breath and thus live in surface waters, went extinct; however, ninety percent of bony fish in the sea survived. Many squids and other cephalopods went extinct. As far as scientists know, no amphibians went extinct. Most turtle species survived.
Alegret et al. sampled several ocean locations and determined that a complete breakdown in photosynthetic activity did not happen in the ocean but that it was moderate and regional. Rather, they proposed that the main cause of extinction was a temporary surface acidification event in the ocean, which caused extinction of shallow water species in the ocean. If so, then why weren’t species in in freshwater lakes and rivers affected? Maruoka and Koeberl proposed that carbonates ejected by the impact were deposited in shallow lakes and rivers first and then neutralized the acidic aerosols when they fell to the lakes; however, the carbonates sank into deeper waters in the ocean and thus did not neutralize the acid that fell into the surface waters of the ocean.[13] Ohno et al. proposed that silicate particles ejected into the atmosphere would have scavenged the sulphuric acid aerosols from the atmosphere and quickly deposited the sulfuric acid in the ocean within a few days of the impact, resulting in highly acidic surface waters in the ocean.[14]
In comparison to the Great Permian extinction, ecosystems recovered quickly after the End Cretaceous Extinction. Ecosystems were fully functioning and robust after 30,000 years. The End Triassic extinction also had a relatively fast recovery of species diversity in comparison to the Great Permian extinction.
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[1] Schoene, Blair, Kyle M. Samperton, Michael P. Eddy, Gerta Keller, Thierry Adatte, Samuel A. Bowring, Syed FR Khadri, and Brian Gertsch. "U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction." Science 347, no. 6218 (2015): 182-184.
[2] Sakamoto, Manabu, Michael J. Benton, and Chris Venditti. "Dinosaurs in decline tens of millions of years before their final extinction." Proceedings of the National Academy of Sciences (2016): 201521478.
[3] Brugger, Julia, Georg Feulner, and Stefan Petri. "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, no. 1 (2017): 419-427.
[4] Zhang, Laiming, Chengshan Wang, Paul B. Wignall, Tobias Kluge, Xiaoqiao Wan, Qian Wang, and Yuan Gao. "Deccan volcanism caused coupled p CO2 and terrestrial temperature rises, and pre-impact extinctions in northern China." Geology 46, no. 3 (2018): 271-274.
[5] Tamara J. Goldin, H. Jay Melosh (2009); Self-shielding of thermal radiation by Chicxulub impact ejecta: Firestorm or fizzle? Geology; 37 (12): 1135–1138. doi: https://doi.org/10.1130/G30433A.1
[6] Morgan, Joanna, Natalia Artemieva, and Tamara Goldin. "Revisiting wildfires at the K‐Pg boundary." Journal of Geophysical Research: Biogeosciences 118, no. 4 (2013): 1508-1520.
[7] Kaiho, Kunio, Naga Oshima, Kouji Adachi, Yukimasa Adachi, Takuya Mizukami, Megumu Fujibayashi, and Ryosuke Saito. "Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction." Scientific reports 6 (2016): 28427.
[8] Kaiho, Kunio, Naga Oshima, Kouji Adachi, Yukimasa Adachi, Takuya Mizukami, Megumu Fujibayashi, and Ryosuke Saito. "Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction." Scientific reports 6 (2016): 28427.
[9] Museum of Paleontology, Berkeley. https://www.prehistoriclife.xyz/extinction/survival-across-the-kt-boundary-at-hell-creek.html
[10] Brusatte, Stephen L., Richard J. Butler, Paul M. Barrett, Matthew T. Carrano, David C. Evans, Graeme T. Lloyd, Philip D. Mannion et al. "The extinction of the dinosaurs." Biological Reviews 90, no. 2 (2015): 628-642.
[11] Schulte P. et al., The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary, Science, 327 (2010) no. 5970: 1214-1218. < http://sciencemag.org/content/327/5970/1214.abstract >
[12] D. Jablonski, Evolutionary consequences of mass extinctions, Patterns and Processes in the History of Life (1986) 36: 313-329.
[13] Maruoka, Teruyuki, and Christian Koeberl. "Acid-neutralizing scenario after the Cretaceous-Tertiary impact event." Geology 31, no. 6 (2003): 489-492.
[14] Ohno, Sohsuke, Toshihiko Kadono, Kosuke Kurosawa, Taiga Hamura, Tatsuhiro Sakaiya, Keisuke Shigemori, Yoichiro Hironaka et al. "Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification." Nature Geoscience 7, no. 4 (2014): 279.
"A diagram showing the diversification of avialans before and after the K-Pg boundary." Credit: JacqCLSin. Used here per CC BY-SA 4.0.