K/T Extinction


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  • The problem with these definitions is that they are too broad. Other factors must be considered.
    Mass extinctions are harder to pin down than it might seem, and the task becomes more difficult the farther one searches back in time.
    Older, more ancient rocks are poorly represented today. Therefore it is hard to clarify if an assemblage went extinct in a short interval or not.
    It is not known for sure how many mass extinctions have occurred throughout history, but good evidence exists regarding the Phanerozioc era.
  • According to Steven Stanley
  • Changing Earth's albedo, and thus its solar budget, and thus its weather
    Producing more continental climates in interiors, changing regional ecosystems
    Change oceanographic conditions, by removing the once-vast epeiric sea systems and by removing a major source of productivity
    Would operate over a 4 million year scale
  • 1980: Walter Alvarez was investigating a layer of clay in Gubbio, Italy at the K/Pg boundary. Wanted to determine length of time represented by the clay layer. Consulted dad (Nobel winning physicist Luis Alvarez) for possible solution. Suggestion:
    1. Meteors impact the Earth's atmosphere all the time2. Some chemical elements more common in meteors and such than on Earth's surface: these should be traceable in minute quantities in sediment3. Find the average infalling rate of these elements today; use this rate and observed amount at the Gubbio clay layer to find out how much time
  • Chances were that the impact was in ocean basins, but most Cretaceous ocean basins have been recycled by plate tectonics
    Some early leads were in Siberia (too early); Manson, Iowa (too small and too early (within Late K))
    Nearly all geological lines of evidence (tektites, tsunami deposits, ejecta deposits, shocked quartz, etc.) were more abundant in Western Hemisphere, and especially in the Gulf of Mexico, than the rest of the world: pointed to impact in that region!
    In Yucatan, Mexico: disrupted layers at K/Pg boundary in buried rock Seismic and gravity scan suggested a crater 180 km across: the right size! Although not visible as a crater because buried under 300-1000 m of Cenozoic rock, it can be seen using sensitive satellite and other data
    Crater was named Chicxulub, after nearby town
  • Quartz is one of the most common of all minerals
    When subjected to intense heat & pressure, forms shock planes
    Shocked quartz has been found in over 100 K/Pg boundary sites worldwide
  • Material thrown up by impact would melt during reentry, form glassy spheres
    These have been found at some K/Pg sites
  • Animals with larger total food requirements die more those with less
    In marine communities, foodwebs tied into photosynthesis (that is, direct from the phytoplankton) would be hit harder than bottom feeders (which feed on the accumulated decayed remains of organisms)
    Additionally, taxa dependant on symbiotic algae would be devastated
    Some geologic record other than just iridium might remain
    Effects would be global and essentially instantaneous: hours to days to months to a few years
  • Thick units probably formed by tsunami found at K/Pg in Carribbean, Gulf Coast of Texas, Mexico, Central America, and South America
    Thinner but widespread deposits of ejecta (material flung through the air) at K/Pg in Carribbean, Gulf Coast of Texas, Mexico, Central America, and South America
  • K/T Extinction

    2. 2. • Occurs when the last representative of a taxon dies. • For Earth History, extinction is the last, or most recent, occurrence of an identifiable fossil.
    3. 3. MASS EXTINCTION • Greater than 50% of all species die at similar time • Geologically short intervals of intense species extinction
    4. 4. Mass Extinction Events of Greatest Severity 60% Terrestrial 90% Marine
    5. 5. Patterns during Mass Extinction Occurs in both terrestrial and marine environments On land, animals suffer yet plants seem highly resistant Disappearance of tropical life forms Tendency of certain animal groups to experience and survive (trilobites and ammonoids) Periodicity in geological time (occurring about every 26 million years)
    6. 6. Extinction Agents • Catastrophic • Extraterrestrial impacts such as meteorites or comet showers • Geologic • Volcanism, glaciation, sea levelvariations, global climactic changes, oxygen/salinity level changes in ocean
    7. 7. K/T Extinction 65 MYA
    8. 8. Victims • • • • • • • • • • • Many species of coccolithophorid: never recover diversity Many species of foram All ammonoids All belemnoids All rudists All plesiosaurs All mosasaurs All pterosaurs All non-flying dinosaurs Several clades of birds Many mammal groups (only monotreme prototheres, multituberculate allotheres, the ancestors and closest relatives of the marsupials among the metatheres, and the ancestors and closest relatives of the placentals among the eutheres)
    9. 9. Proposed Causes: The Maastrichtian Regression Draining of epeiric seas would alter terrestrial climate
    10. 10. Increased Maastrichtian volcanism, especially the Deccan Traps • • • Decrease insolation (incoming sunlight) by presence of fine particles in high atmosphere Also change Earth's albedo, although not as dramatically Would operate on the scale of a few tens of thousands to hundreds of thousands of years
    11. 11. The Chicxulub Impact • 1980 – Walter Alvarez • Hypothesized: an asteroid impacted Earth at the K/T boundary • Evidence: • Iridium • Shocked Quartz • Tektites
    12. 12. Chicxulub Crater 10-15 km diameter (size of Manhattan)
    13. 13. Iridium Platinum-like metal, common in metallic asteroids but very rare in Earth's crust.
    14. 14. Shocked Quartz
    15. 15. Tektites
    16. 16. Tektites
    17. 17. Probable Effects Short term: • Release lots of energy near impact, form huge crater: 1.8 x 108 megatons!! • Burst of light would vaporize material for kilometers around, just like thermonuclear weapons • Blast wave would devastate nearby region; it would be felt around the world, but decrease with distance • Shockwaves from impact would generate huge tsunamis ("tidal" waves)
    18. 18. Longer term: • Material vaporized by impact kicked high up in atmosphere: reduced amount of incoming sunlight • • • • Observations on Mars showed big temperature drops due to high-level particles In human history, eruption of Tambora in Indonesia in 1815 produced chilling effects worldwide for more than a year later Dust and ash would block out sunlight, reducing photosynthesis and killing off plants on land and surface algae in water; herbivores feeding on these would die; carnivores feeding on these would starve (after a brief feast) Collapse of foodwebs would require long term to
    19. 19. Tsunami
    20. 20. Crater Animation BOOM!