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K/T Extinction BoundaryK/T Extinction Boundary

65 million years ago,earth experienced aglobal mass extinctionevent: dinosaurs

disappeared that extinction defines theboundary between theCretaceous and Tertiary(abbreviated K and T)geological periods and, a

broader scale, theboundary between theMesozoic and Cenozoiceras.

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The cause of the K-T extinctions is one of

the great mysteries in science, and

scientists have proposed many kinds oftheories to account for it. They range from

asteroid or comet impacts, volcanism, sea

level changes, supernova explosions, and

on and on.

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What Is a Mass Extinction?What Is a Mass Extinction?

an episode in evolutionary history where

more than 50% of all known species living

at that time went extinct in a short periodof time (less than 2 million years or so).

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PermianPermian--Triassic extinctionTriassic extinction

Life on Earth nearly

was wiped out -- an

estimated 90% of all

species living at thattime were

extinguished.

Trilobites were the

dominant marine

organism; wiped out.

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CSI: Dinosaur DemiseCSI: Dinosaur Demise

The Fossil Record - It's not perfect, gaps

Time Resolution: gets worse with increasing

age; gradual decline of dinosaurs vs. a sudden

cataclysm is almost intractable

Falsifiability - Sad but true: many hypotheses

about dinosaur extinction sound quite convincing

and might even be correct, but, as you know, arenot really science if they cannot be tested and

falsified if untrue.

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Wrong Hypotheses That HaveWrong Hypotheses That Have

Been TestedBeen Tested

Dinosaurs got so darned big that they

crushed themselves

Mammals outcompeted the dinosaurs Mammals ate all of the dinosaurs eggs

Cosmic rays killed the dinosaurs

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Common GroundCommon Ground

There was global climatic change; theenvironment changed from a warm, mild one inthe Mesozoic to a cooler, more varied one in the

Cenozoic Many organisms; both marine and terrestrial,

vertebrate and invertebrate; went extinct

At or near the K/T boundary, there was iridium,

shocked quartz, tektites, and a soot layer wasfound in many areas (evidence for widespreadforest fires), all consistent with a catastrophicevent

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Iridium spike at K/T boundaryIridium spike at K/T boundary

Iridium is an element

that occurs in the

Earths crust in only

tiny proportions, but ismuch more common

in chondrite

meteorites.

Deep volcanoes also

a source

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Shocked QuartzShocked Quartz

High pressures causewhat is known as shockmetamorphism, thisdeforms the structure of

the quartz and createsparallel laminar ripples.

It is found all over theworld, not just locally.

No other process on theplanet creates this type ofquartz.

Meteors; volcanoes?

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TEKTITESTEKTITES

Tektites are naturally

occurring silica glass

formed during the

impact of a meteor.

Also formed from

volcanic eruptions

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Cosmic CatastrophesCosmic Catastrophes

Tektites are formed whenmolten material isinjected into theatmosphere and coolsbefore touching theground

Volcanoes, meteors are asource

Psychically they are usedfor extraterrestrial

communication, astraltravel, and luciddreaming.

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Dinosaurs on FireDinosaurs on Fire

There is a large sootlayer associated with theK/T boundary.

This layer is consistent

with catastrophic firesthat may have swept thesurface of the earth atthis time.

Such a fire would havekilled most large

terrestrial animals.

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Nuclear WinterNuclear Winter

Lingering airborne

debris is believed to

have triggered

darkness and adecline in the global

temperature

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Intrinsic Gradualists: CSIIntrinsic Gradualists: CSI

VolcanoesVolcanoes

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Deccan Traps VolcanismDeccan Traps Volcanism

About 65 million years ago,

the mantle plume that

gave rise to the Reunion

hotspot volcano burned

its way through earth's

crust, flooding western

India and surrounding

areas with the Deccan

Traps flood basalts.

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Deccan Traps VolcanismDeccan Traps Volcanism

Rapid eruption of the vast Deccan Traps lava fieldswould have flooded earth's surface with CO2,overwhelming surficial systems and sinks, triggeringrapid K-T transition greenhouse warming, chemical

changes in the oceans (McLean, 1985a, b, c; 1988,1995), and the K-T mass extinctions.

This increased volcanism could have created enoughdust and soot to block out sunlight; contributing to theclimatic change.

Source of Iridium; can explain iridium spike

Source of tektites

Shocked quartz; maybe a source

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Plate TectonicsPlate Tectonics

Major changes in theorganization of the continentalplates (continental drift) wereoccurring at the K-T boundary.

The oceans (especially theInterior Seaway in NorthAmerica) were experiencing aregression; they were recedingfrom the land. A less mildclimate would have been theresult, and this would have

taken a long time. Major plate activity is

consistent with major volcanicactivity

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Extrinsic Catastrophists: CSIExtrinsic Catastrophists: CSI

AsteroidsAsteroids

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Extrinsic CatastrophistsExtrinsic Catastrophists

This side of the controversy holds that the

ultimate cause of the K-T extinction was

extrinsic, meaning of an extraterrestrial

nature, and catastrophic, meaning fairly

sudden and punctuated. The main

hypothesis was proposed in 1980 by

(among others) Luis and Walter Alvarez,geologists at the University of California at

Berkeley.

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The Alvarez HypothesisThe Alvarez Hypothesis

A large extraterrestrial objectcollided with the Earth, its impactthrowing up enough dust to causethe climatic change.

The iridium layer is what promptedthe Alvarez team to blame an

asteroid impact for the extinction --asteroids and similarextraterrestrial bodies are higherin iridium content than the Earth'scrust, so they figured that theiridium layer must be composed ofthe dust from the vaporizedmeteor.

No crater was found, but it wasassumed that one existed thatwas about 65 million years old and100 kilometers (about 65 miles) indiameter.

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Where Is the Smoking Gun?Where Is the Smoking Gun?

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Subducted? Evidence removed!Subducted? Evidence removed!

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CHICXULUB CRATERCHICXULUB CRATER

Survey work related to oil

exploration in 1981 first

identified concentric rings

of gravitational anomalies

around the northwest

coast of Yucatan.

Hildebrand (1991)

located two concentric

rings which suggested anouter rim of 180 km.

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The Smoking Gun!The Smoking Gun!

Some 65 million yearsago, a 10 to 12 km in sizeasteroid or cometcrashed on the Yucatan

platform and formed the >200 km in diameterChicxulub crater.

If a 10km diameter objectimpacted at the point at

which it struck it wouldhave a velocity of roughly100,000 km/h.

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Magnitude of ImpactMagnitude of Impact

The K/T impact, as it

is now referred to,

resulted in 100 million

megatons of energy. Equivalent to the

energy of 300 million

nuclear weapons

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Impact ForcesImpact Forces

Computer model of

the Chicxulub impact

showing the raising

fireball and CO2plumes and ejecta

curtain material (from

Alvarez, Claeys and

Kieffer, Science 1995)

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CONCLUSIONSCONCLUSIONS

There has been no settlement to the issueso far, and no clear one is foreseeable.Both sides claim to hold the majority of

proponents in science; it seems that(greatly over- generalizing) manypaleontologists lean towards the intrinsicside, while many astronomers and

physicists favor the extrinsic side, andgeologists are probably evenly splitbetween the two.