Presentation on theme: "The K-T Extinction Christina Davis Katie Peth 19 April 2012."— Presentation transcript:
The K-T Extinction Christina Davis Katie Peth 19 April 2012
K Abbreviation for Cretaceous Period, derived from the German name Kreidezeit T Abbreviation for the Tertiary Period historical term for period of time covered by the Paleogene and Neogene periods es/interviews/extinction_graph3.gif
Also referred to as the Cretaceous–Paleogene extinction event Approximately 65.5 million years ago Associated with geological signature K–T boundary: thin band of sedimentation found in various parts of world K-T Extinction
K-T Extinction Numerous 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 event Very small number of dinosaur fossils have been found above the K–T boundary (reworked fossils) eroded from their original locations then preserved in later sedimentary Littlefoot, Cera, Spike, Ducky, Petri
Others That “Moved On” Mosasaurs, plesiosaurs, pterosaurs, various plants and invertebrates became extinct Juvenile Plesiosaur Plesiosaur fossil Taniwhasaurus Prognadothon
More Casualties Azhdarchidae (Pterosaur) Rudist Bivalve Belemnites (cephalopod) Ammonite Fossil
Mammals! 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!)
Potential 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 extinction These events would have released massive amounts of dust and ash released into the atmosphere Reduced surface sunlight Hindered photosynthesis Disruption of Earth’s biosphere MacLeod, N. J. Geo. Soc. 1997, 154,
Controversy Many believe the extinction was more gradual from the sea level and climate changes, and aggravated by impact events or increased volcanic activity Length of time for extinction to occur is controversial Signor-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 extinction Several million years before to few million years after
Mass extinction of dinosaurs (etc.) caused by impact of large asteroid on Earth 65 million years ago Named 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 Alvarez Hypothesis
Evidence? 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/comets Also found chromium isotopic anomalies similar to those found in carbonaceous chondrites, along with shocked quartz granules and tektites. Alvarez, L.W. Science. 1980, 208,
Alvarez 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 energy 1 x 10 8 megatons, 2 million times greater than most powerful thermonuclear bomb tested! Alvarez, L.W. Science. 1980, 208,
Chicxulub Crater Impact 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 quartz Tektites Gravity anomaly
Created sunlight blocking dust cloud Affects photosynthesis, leading to extinction of plants, phytoplankton and other organisms dependent on it. Sulfur aerosols (12 years to dissipate) 10–20% reduction of solar transmission Global firestorms exacerbated by high O 2 concentration Increase in CO 2, greenhouse effect once cloud settled Reduced global temperature (impact winter) Acid rain (relatively minor impact) + megatsunamis! Alvarez Impact Kring, D.A. Astrobiology. 2003, 3,
Alvarez Impact Hypothesis that impact forming Chicxulub crater was caused by asteroid from Baptistina family of asteroids 2011 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 extinction The 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 Nagasaki Still controversy on whether a single impact was the sole cause.
Large igneous province located on the Deccan Plateau of west- central India One of the largest volcanic features on Earth Multiple layers of solidified flood basalt more than 2,000 m thick with an area of 500,000 km 2 and a volume of 512,000 km 3
Common extrusive volcanic rock Basalt
“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 change Average fall in temperature of 2 °C in this period Deccan Traps
MULTIPLE IMPACT live/photos/000/010/cache/mass- extinction_1077_600x450.jpg Multiple Impact Theory
Simultaneous impacts around the K-T boundary Asteroids/comets Boltysh 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.
Shiva Crater 500 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 iridium Many remain unconvinced; “Shiva Crater” not recognized as an impact crater by the Earth Impact Database.
Maastrichtian was the final part of the Cretaceous period Between 72 to 66 million years ago Exposed 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 time Hypothesis: mid-ocean ridges became less active and thus sunk under their own weight causing marine life form extinction Maastrichtian Sea Level
Cosmic radiation from a nearby supernova explosion Fallout from a supernova explosion should contain 244 Pu, the longest-lived plutonium isotope (half-life of 81 million years) If this hypothesis were correct, detectable traces of 244 Pu should be detected from rocks deposited at the time However, there is an absence of 244 Pu, disproving this hypothesis Supernova Hypothesis
Multiple Causes? Mixture of previously mentioned causes
I Will Survive! Microbiota Radiolaria, Diatoms, benthic foraminifera Marine Invertebrates Brachiopods, nautiloids, coleoids Fish 80% of cartilaginous fish 90% of teleost fish
I Will Survive! Terrestrial Invertabrates Terrestial Plants Paleocene recovery of plants began with recolonizations by fern species Saprotrophic organisms Polyploidy Amphibians
I Will Survive! Non-archosaur reptiles Testudines (turtles) Lepidosaurs (snakes and lizards) Choristoderes Archosaurs Crocodilians Dinosaurs (Birds) Mammals! Diversification stalled.
Conclusions Most accepted reason is the Alvarez Impact Theory Most likely mixture of this impact and volcanic activity Supernova not supported with scientific evidence Ability to survive depended on food source, size, environment Feed on snails or other detritus species Tiny is best Stable to environmental changes