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CRETACEOUS-TERTIARY EXTINCTION
GLY 5020 EARTH HISTORY – DR. FARLEY
UNIVERSITY OF NORTH CAROLINA PEMBROKE
FALL 2009
SARAH SEALEY
•Occurs when the last representative of a taxon dies.
•For Earth History, extinction is the last, or most recent, occurrence of an identifiable fossil.
MASS EXTINCTION•Greater than 50% of all species die at similar
time
•Geologically short intervals of intense species extinction
Mass Extinction Events of Greatest Severity
60% Terrestrial 90% Marine
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)
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
K/T Extinction 65 MYA
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)
Proposed Causes: The Maastrichtian Regression
Draining of epeiric seas would alter terrestrial climate
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
The Chicxulub Impact
•1980 – Walter Alvarez
•Hypothesized: an asteroid impacted Earth at the K/T boundary
•Evidence:
•Iridium
•Shocked Quartz
•Tektites
Chicxulub Crater10-15 km diameter (size of Manhattan)
Iridium Platinum-like metal,
common in metallic asteroids but very rare in Earth's crust.
Platinum-like metal, common in metallic asteroids but very rare in Earth's crust.
Shocked Quartz
Tektites
Tektites
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)
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)
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 recover, as many parts of each foodchain might be lost
•Additional possible effects include:
•Superacid rain
•Global firestorms
•Global tsunami
Tsunami
Crater AnimationBOOM!