Mass extinction 4.ppt [Read-Only]

Mass Extinction
John Phillips
(1801-1900)
Life on the Earth:
Its Origin and Succession
(1860)
http://www.strangescience.net/phillips.htm
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The “rediscovery” of mass
extinction – the 1980s
• 1980 – The Alvarez hypothesis
• 1982 – The “big 5” (Raup and Sepkoski)
• 1984 – 26 my periodicity (Raup and Sepkoski)
Mass Extinction
“… any substantial increase in the amount of extinction
(i.e., lineage termination) suffered by more than one
geographically widespread higher taxon during a relatively
short interval of geologic time, resulting in an at least
temporary decline in standing diversity.”
(David Jablonski, 1986)
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The Big 5 Mass Extinctions
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Mass Extinction
“… any substantial increase in the amount of extinction
(i.e., lineage termination) suffered by more than one
geographically widespread higher taxon during a relatively
short interval of geologic time, resulting in an at least
temporary decline in standing diversity.”
(David Jablonski, 1986)
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The end-Ordovician event
• Victims:
–
–
–
–
trilobites
brachiopods
corals
cephalopods
End-Ordovician Victims
Ordovician Trilobite,
Brachiopods
and Corals
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The end-Ordovician event
• Possible causes
– Climatic cooling due to glaciation
– Extraterrestrial gamma radiation ??
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The Big 5 Mass Extinctions
The Late Devonian event
• Victims:
–
–
–
–
–
trilobites
brachiopods
corals
cephalopods
fish
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Late Devonian Victims
Devonian Trilobites, Fish,
Coral, and Brachiopods
The late Devonian event
• Possible causes
–
–
–
–
volcanism
extraterrestrial impact
climatic cooling
ocean anoxia
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Possible Devonian Impact Craters
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Manicouagan Crater, Quebec
The Big 5 Mass Extinctions
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The end-Permian event
• Victims:
–
–
–
–
–
–
trilobites*
brachiopods
corals*
cephalopods
fusulinid foraminifera*
echinoderms
• crinoids
• blastoids*
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End-Permian Victims
Blastoids, Fusulinids, Trilobites,
Brachiopods, Corals, Crinoids
The end-Permian event
• Possible causes
–
–
–
–
–
volcanism
extraterrestrial impact
sea level fall
ocean chemistry changes (esp. CO2)
“the murder on the Orient Express hypothesis”
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Buckminsterfullerenes
(“Buckeyballs”)
science.nasa.gov/headlines/ y2001/ast23feb_1.htm
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The Big 5 Mass Extinctions
The end-Triassic event
• Victims:
– clams
– ammonoid cephalopods
– terrestrial reptiles
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End-Triassic Victims
Bivalves, Therapsids,
Ammonites, Phytosaurs
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The end-Triassic event
• Possible causes
– volcanism
– extraterrestrial impact
– ocean anoxia
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Basaltic dike, Bay of Fundy
The Palisades
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The Big 5 Mass Extinctions
The end-Cretaceous event
• Victims:
–
–
–
–
–
–
–
–
rudistid clams*
other clams, snails, echinoids
ammonoid cephalopods*
marine plankton
dinosaurs*
flying reptiles*
plesiosaurs, ichthyosaurs*
terrestrial plants
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End-Cretaceous Victims
Rudist bivalves, foraminifera,
ammonites, snails, mosasaurs, plesiosaurs,
dinosaurs, pterosaurs, icthyosaurs
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The end-Cretaceous event
• Possible causes
– extraterrestrial impact
Hypotheses of
K-T extinction
prior to 1980
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Walter and Luis
Alvarez
The Iridium anomaly
The K-T Boundary
Stevns Klint, Denmark
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The K-T Boundary
Stevns Klint, Denmark
K-T Boundary in Montana
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Meteor Crater, AZ
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Evidence for impact at the K-T
•
•
•
•
•
•
Iridium anomaly (“spike”)
Shocked quartz
Microtectites/spherules
Impact crater
Pieces of the asteroid/meteorite (?)
Evidence for tsunamis
Chicxulub
Teapot Dome, Wyoming
Shocked Quartz Grains
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The Chicxulub
Impact Site
Structure of the Chicxulub Structure
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Drilling Through
the Chicxulub Structure
This three-dimensional map of local gravity and magnetic field
variations around Chicxulub, viewed obliquely from approximately
60° above the surface looking north, with artificial lighting from the south.
(Courtesy of V. L. Sharpton, LPI)
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What would the
effects of a large
bolide impact be?
Brazos River, Texas
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Altered tektites from the Chicxulub impact deposited at Dogie Creek,
Wyoming. The scale bar shows millimeters.
K-T Volcanism
The Deccan Traps
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The Effects of Mass Extinction
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Dinosaur Valley State Park, Glen Rose, TX
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So What?
• Mass extinctions are unusual, but have
occurred multiple times in Earth history.
• They are different from “background
extinction”, which occurs all the time.
• Mass extinctions always have large effects.
• Those effects are unpredictable.
• If a mass extinction is large enough, it can
completely disrupt the biosphere
permanently.
So What ? (continued)
• There are probably multiple causes of mass
extinction.
• At least one mass extinction (the K-T) was
caused by extraterrestrial impact.
• The current episode of mass extinction has
the potential to disrupt the biosphere in
major and unpredictable ways.
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http://www.mpm.edu/reef/reef-extinction-chart.gif
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