ExtinctionExtinction

I. Patterns of ExtinctionI. Patterns of Extinction

II. Causes of ExtinctionII. Causes of Extinction

Types of Extinction EventsTypes of Extinction Events

•• Background ExtinctionBackground Extinction

•• Mass ExtinctionMass Extinction

[Source: [Source: RaupRaup and and SepkoskiSepkoski 1982, 1982, ScienceScience 215, 1501215, 1501--1503]1503]

Rates of ExtinctionRates of Extinction

[Source: [Source: RaupRaup and and SepkoskiSepkoski 1982, 1982, ScienceScience 215, 1501215, 1501--1503]1503]

Rat

e of

Ext

inct

ion

(per

106

year

s)

Geological Time (106 years)

Mass ExtinctionsMass Extinctions

•• OrdovicianOrdovician--Silurian (439 Silurian (439 myamya))•• Late Devonian (364 Late Devonian (364 myamya))•• PermianPermian--Triassic (251 Triassic (251 myamya))•• End Triassic End Triassic (200(200--215 215 myamya))•• CretaciousCretacious--Tertiary Tertiary (65 (65 myamya))

[Source: [Source: RaupRaup and and SepkoskiSepkoski 1982, 1982, ScienceScience 215, 1501215, 1501--1503]1503]

[Source: [Source: RaupRaup and and SepkoskiSepkoski 1986, 1986, ScienceScience 231, 833231, 833--836]836]

Periodicity of Mass ExtinctionsPeriodicity of Mass Extinctions

Causes of ExtinctionCauses of Extinction

•• BioticBioticcaused by interactions with other caused by interactions with other speciesspecies

•• AbioticAbioticcaused by physical disturbances caused by physical disturbances resulting in environmental changeresulting in environmental change

Hypothetical Causes of Mass ExtinctionHypothetical Causes of Mass Extinction

•• Volcanic ActivityVolcanic Activity

•• Changes in Sea LevelChanges in Sea Level

•• Impacts of AsteroidsImpacts of Asteroids

The Asteroid Impact TheoryThe Asteroid Impact Theory

•• Proposed by Louis and Walter Proposed by Louis and Walter Alvarez, who discovered a Alvarez, who discovered a strange layer of clay that strange layer of clay that separated older rock that was separated older rock that was rich in species from earlier rock rich in species from earlier rock that was poor in species. that was poor in species.

•• A single large asteroid struck the earth causing A single large asteroid struck the earth causing catastrophic changes in the environment.catastrophic changes in the environment.

KK--T BoundaryT Boundary

[Source: Alvarez et al. 1980, [Source: Alvarez et al. 1980, ScienceScience 208, 1095208, 1095--1108]1108]

Evidence for Asteroid ImpactEvidence for Asteroid Impactat the Kat the K--T Boundary*T Boundary*

•• Elevated levels of IridiumElevated levels of Iridiumrare on earth but common within asteroidsrare on earth but common within asteroids

•• Metamorphic rockMetamorphic rockShocked quartz and glass particlesShocked quartz and glass particles

•• Unique form of CarbonUnique form of CarbonA chemical form that composes soot, suggesting firesA chemical form that composes soot, suggesting fires

*Based on over 120 samples taken worldwide*Based on over 120 samples taken worldwide

Meteor impacts vary Meteor impacts vary greatly in magnitude.greatly in magnitude.

Effects of a Major Asteroid ImpactEffects of a Major Asteroid Impact

•• DarknessDarkness

•• ColdCold

•• Drop in Sea LevelDrop in Sea Level

•• Acid RainAcid Rain

These effects may have lasted from 5These effects may have lasted from 5--50 years.50 years.

Our Very Own Asteroid BeltOur Very Own Asteroid Belt

The current mass extinction has a biotic cause.The current mass extinction has a biotic cause.

The Good News:The Good News:Everything will be OK in 20 millions years.Everything will be OK in 20 millions years.

[Source: Kirchner & Weil 2000, [Source: Kirchner & Weil 2000, NatureNature 404, 177]404, 177]