3K-T ExtinctionKAbbreviation for Cretaceous Period, derived from the German name KreidezeitTAbbreviation for the Tertiary Periodhistorical term for period of time covered by the Paleogene and Neogene periods
4K-T ExtinctionAlso referred to as the Cretaceous–Paleogene extinction eventApproximately 65.5 million years agoAssociated with geological signatureK–T boundary: thin band of sedimentation found in various parts of world
6K-T ExtinctionNumerous groups of organisms went extinct, most notably the non-avian dinosaurs.Non-avian dinosaur fossils are only found below K-T boundary indicating they became extinct during boundary eventVery small number of dinosaur fossils have been found above the K–T boundary (reworked fossils)eroded from their original locations then preserved in later sedimentaryLittlefoot, Cera,Spike, Ducky, Petri
9Others That “Moved On”Mosasaurs, plesiosaurs, pterosaurs, various plants and invertebrates became extinctPrognadothonPlesiosaur fossil---Numerous species of benthic foraminifera became extinct during the K–Pg event, presumably because they depend on organic debris for nutrients, since the biomass in the ocean is thought to have decreased.----Ostracods, a class of small crustaceans that were prevalent in the upper Maastrichtian, left fossil deposits in a variety of locations. A review of these fossils shows that ostracode diversity was lower in the Paleocene than any other time in the Tertiary. However, current research cannot ascertain whether the extinctions occurred prior to or during the boundary interval itself.2627----Approximately 60% of late-Cretaceous Scleractinia coral genera failed to cross the K–T boundary into the Paleocene. Further analysis of the coral extinctions shows that approximately 98% of colonial species, ones that inhabit warm, shallow tropical waters, became extinct. Colonial coral species rely upon symbiosis with photosynthetic algae, which collapsed due to the events surrounding the K–T boundary.2829 However, the use of data from coral fossils to support K–Pg extinction and subsequent Paleocene recovery must be weighed against the changes that occurred in coral ecosystems through the K–T boundary.7----- Except for nautiloids (represented by the modern order Nautilida) and coleoids (which had already diverged into modern octopodes, squids, and cuttlefish) all other species of the molluscan class Cephalopoda became extinct at the K–T boundary. These included the ecologically significant belemnoids, as well as the ammonoids, a group of highly diverse, numerous, and widely distributed shelled cephalopods---- Approximately 35% of echinoderm genera became extinct at the K–T boundary-----Approximately 35% of echinoderm genera became extinct at the K–T boundary, although taxa that thrived in low-latitude, shallow-water environments during late Cretaceous had the highest extinction rate. Mid-latitude, deep-water echinoderms were much less affected at the K–T boundary. The pattern of extinction points to habitat loss, specifically the drowning of carbonate platforms, the shallow-water reefs in existence at that time, by the extinction event.32Other invertebrate groups, including rudists (reef-building clams) and inoceramids (giant relatives of modern scallops), also became extinct at the K–T boundary.3334---- In North America, approximately 57% of plant species became extinct.-----Only one family of pterosaurs, Azhdarchidae, was definitely present in the Maastrichtian, and it became extinct at the K–T boundary. These large pterosaurs were the last representatives of a declining group that contained 10 families during the mid-Cretaceous. Smaller pterosaurs became extinct prior to the Maastrichtian during a period that saw a decline in smaller animal species while larger species became more prevalent. While this was occurring, modern birds were undergoing diversification and replacing archaic birds and pterosaur groups, possibly due to direct competition, or they simply filled empty niches---- However, all non-neornithean birds became extinct, including flourishing groups like enantiornithines and hesperornithiforms.55Juvenile PlesiosaurTaniwhasaurus
10Azhdarchidae (Pterosaur) More CasualtiesRudist BivalveBelemnites(cephalopod)Azhdarchidae (Pterosaur)Ammonite Fossil
11Mammals!Mammalian clades passed through boundary with few extinctions (see Katie’s shirt)Mammalian clades then thrived and evolved, along with other species (more on that later!)
12Potential Causes One or more catastrophic events? Asteroid impacts? Increased volcanic activity?Several impact craters and massive volcanic activity have been dated to the approximate time of extinctionThese events would have released massive amounts of dust and ash released into the atmosphereReduced surface sunlightHindered photosynthesisDisruption of Earth’s biosphereMacLeod, N. J. Geo. Soc. 1997, 154,
13ControversyMany believe the extinction was more gradual from the sea level and climate changes, and aggravated by impact events or increased volcanic activityLength of time for extinction to occur is controversialSignor-Lipps effect: the fossil record is so incomplete that most extinct species probably died out long after the most recent fossil that has been found.There are very few continuous beds of fossil-bearing rock from before and after K-T extinctionSeveral million years before to few million years after
17Alvarez HypothesisMass extinction of dinosaurs (etc.) caused by impact of large asteroid on Earth 65 million years agoNamed for Nobel-prize winning physicist Luis Alvarez who first suggested theory in 1980, along with geologist son Walter Alvarez and chemists Frank Asaro and Helen Michels
18Evidence?K-T boundary sedimentary band all over the world has iridium ranging from times normal amount.Iridium is rare in Earth’s crust, but abundant in asteroids/cometsAlso found chromium isotopic anomalies similar to those found in carbonaceous chondrites, along with shocked quartz granules and tektites.Alvarez, L.W. Science. 1980, 208,
19Alvarez Impact Able to calculate size of meteor Would have to be km in diameter (size of Mars moon Deimos, or Manhattan)Impact of that size would have an incredible amount of energy1 x 108 megatons, 2 million times greater than most powerful thermonuclear bomb tested!Alvarez, L.W. Science. 1980, 208,
21Chicxulub CraterImpact site buried underneath Yucatán peninsula in Mexico, discovered by geophysicist Glen Penfield in the late 1970s.Took about 20 years to fully investigate crater, with help from Alan Hildebrand.Evidence for impact:Shocked quartzTektitesGravity anomaly
22Kring, D.A. Astrobiology. 2003, 3, 133-152 Alvarez ImpactCreated sunlight blocking dust cloudAffects photosynthesis, leading to extinction of plants, phytoplankton and other organisms dependent on it.Sulfur aerosols (12 years to dissipate)10–20% reduction of solar transmissionGlobal firestorms exacerbated by high O2 concentrationIncrease in CO2, greenhouse effect once cloud settledReduced global temperature (impact winter)Acid rain (relatively minor impact) + megatsunamis!Kring, D.A. Astrobiology , 3,
23Alvarez Impact2007- Hypothesis that impact forming Chicxulub crater was caused by asteroid from Baptistina family of asteroids2011 WISE study begs to differ.scientists reviewed 20 years of literature to rule out massive volcanism as cause.Also endorsed that the asteroidal impact at Chicxulub crater as being the cause of the extinctionThe collision would have released the same energy as 100 teratonnes of TNT (420 ZJ), over a billion times the energy of the bombs dropped on Hiroshima and NagasakiStill controversy on whether a single impact was the sole cause.
25Deccan TrapsLarge igneous province located on the Deccan Plateau of west- central IndiaOne of the largest volcanic features on EarthMultiple layers of solidified flood basaltmore than 2,000 m thick with an area of 500,000 km2 and a volume of 512,000 km3
27Deccan Traps“Trap” is derived from the Swedish word for stairs and refers to the step-like hills forming the landscape of the region.Release of volcanic gases, particularly sulfur dioxide, during formation of traps contributed to contemporary climate changeAverage fall in temperature of 2 °C in this period
29Multiple Impact Theory live/photos/000/010/cache/mass- extinction_1077_600x450.jpg
30Multiple Impact Theory Simultaneous impacts around the K-T boundaryAsteroids/cometsBoltysh Crater (Ukraine)Silver Pit Crater (North Sea)Shiva Crater (Indian Ocean, controversial origin)Could have had more formed in Tethys Ocean obscured by tectonic effects.
31Shiva Crater500 km in diameter, hypothesized by Sankar Chatterjee to be result of impact with 40 km asteroid.Unusually rectangular, with large amounts of alkaline melt rocks, shocked quartz, and iridiumMany remain unconvinced; “Shiva Crater” not recognized as an impact crater by the Earth Impact Database.
32Maastrichtian Sea Level Maastrichtian was the final part of the Cretaceous periodBetween 72 to 66 million years agoExposed rock layers do not show the kind of erosion, tilting, distortion and other geologic patterns that are common with formation of mountains.Evidence that sea levels fell dramatically during this timeHypothesis: mid-ocean ridges became less active and thus sunk under their own weight causing marine life form extinction
33Supernova HypothesisCosmic radiation from a nearby supernova explosionFallout from a supernova explosion should contain 244Pu, the longest-lived plutonium isotope (half-life of 81 million years)If this hypothesis were correct, detectable traces of 244Pu should be detected from rocks deposited at the timeHowever, there is an absence of 244Pu, disproving this hypothesis
34Multiple Causes?Mixture of previously mentioned causes
35I Will Survive! Microbiota Radiolaria, Diatoms, benthic foraminifera Marine InvertebratesBrachiopods, nautiloids, coleoidsFish80% of cartilaginous fish90% of teleost fish
36I Will Survive! Terrestrial Invertabrates Terrestial Plants Paleocene recovery of plants began with recolonizations by fern speciesSaprotrophic organismsPolyploidyAmphibians
37I Will Survive! Non-archosaur reptiles Testudines (turtles) Lepidosaurs (snakes and lizards)ChoristoderesArchosaursCrocodiliansDinosaurs (Birds)Mammals!Diversification stalled.
38Conclusions Most accepted reason is the Alvarez Impact Theory Most likely mixture of this impact and volcanic activitySupernova not supported with scientific evidenceAbility to survive depended on food source, size, environmentFeed on snails or other detritus speciesTiny is bestStable to environmental changes