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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 massextinction – 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 relativelyshort interval of geologic time, resulting in an at leasttemporary 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 relativelyshort interval of geologic time, resulting in an at leasttemporary decline in standing diversity.”

(David Jablonski, 1986)

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The end-Ordovician event

• Victims:– trilobites– brachiopods– corals– cephalopods

Ordovician Trilobite,Brachiopodsand Corals

End-Ordovician Victims

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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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Devonian Trilobites, Fish,Coral, and Brachiopods

Late Devonian Victims

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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science.nasa.gov/headlines/ y2001/ast23feb_1.htm

Buckminsterfullerenes(“Buckeyballs”)

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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 ofK-T extinction prior to 1980

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Walter and Luis Alvarez

The Iridium anomaly

The K-T BoundaryStevns Klint, Denmark

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The K-T BoundaryStevns 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

Shocked Quartz Grains

Chicxulub

Teapot Dome, Wyoming

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The ChicxulubImpact 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 approximately60° above the surface looking north, with artificial lighting from the south. (Courtesy of V. L. Sharpton, LPI)

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What would theeffects of a largebolide 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 biospherepermanently.

So What ? (continued)

• There are probably multiple causes of massextinction.

• At least one mass extinction (the K-T) wascaused by extraterrestrial impact.

• The current episode of mass extinction hasthe potential to disrupt the biosphere inmajor and unpredictable ways.

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http://www.mpm.edu/reef/reef-extinction-chart.gif