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Mass Extinction ASTR 1420 Lecture 9 Sections : 4.6, 6.4, 11.3

Mass Extinction

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Mass Extinction. ASTR 1420 Lecture 9 Sections : 4.6, 6.4, 11.3. Mass Extinctions in the Earth History. Mass Extinctions. Check http://en.wikipedia.org/wiki/Impact_event http://en.wikipedia.org/wiki/Mass_extinction. - PowerPoint PPT Presentation

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Page 1: Mass Extinction

Mass Extinction

ASTR 1420

Lecture 9

Sections : 4.6, 6.4, 11.3

Page 2: Mass Extinction

Mass Extinctions in the Earth History

Page 3: Mass Extinction

Mass ExtinctionsCheck • http://en.wikipedia.org/wiki/Impact_event• http://en.wikipedia.org/wiki/Mass_extinctio

n

•Over 99% of species that ever lived are now extinct, but extinction occurs at an uneven rate.•During the past 550 Myrs, there were five

mass extinction events when more than 50% of animal species died.

Page 4: Mass Extinction

Permian Extinction : “Great Dying”

• 96% all marine species and 70% land species died.• The "Great Dying" had enormous evolutionary significance: on land it

ended the dominance of mammal-like reptiles and created the opportunity for archosaurs and then dinosaurs to become the dominant land vertebrate

Page 5: Mass Extinction

K-T Extinction : End of dinosaurs

• 65 Myrs ago, 75% of species died. • Ending the reign of dinosaurs and started the world of mammals and birds.

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What’s the cause? Temperature?

Not all major mass extinctions coincide with sudden changes in temperature! Then, why?

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Asteroid Impact! (for some cases, but not for all!)

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Causes• Flood basalt event (11 occurrences all coincide with extinction events)

Large magma flood ashes, dust prevent photosynthesis destroy food chain ; CO2 emission and acid rain also.

Page 9: Mass Extinction

Causes • Sea-level falls (7 matches out of 12 cases)

destroy continental shelf area! disrupt weather pattern

Page 10: Mass Extinction

Causes • Impact events (1-50)• Ice ages

Hothouse (methane gun)

Methane clathrate (aka, methane ice, methane is a 20 times more efficient agent for greenhouse effect)

Nearby supernova or Gamma ray burst

Page 11: Mass Extinction

Chicxulub Impact (= dinosaur killer, K-T impact)• ~180km in diameter• Recent discovery (1978)

• Equals to the energy of 10,000+ times of all nuclear weapon detonations

Page 12: Mass Extinction

Some recent impacts!• Arizona (Barringer Crater)• ≈4,000 ft diameter• 50m size iron meteor collided at a

speed of ~20km/sec. • ~50,000 yrs ago

• Tunguska (June 30, 1908, Siberia)• Burst meteor in the air (~5 miles)• About 1,000 times stronger than

the Hiroshima bomb.• Knocked off about 80 million trees

within 15miles

Page 13: Mass Extinction

Shoemaker-Levy

Page 14: Mass Extinction

Happens frequently…• A chain of impact craters

on Ganymede

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Torino scaleA method for categorizing the impact hazard of near-Earth objects (NEOs). assessing the seriousness of collision predictions by combining probability statistics and known kinetic damage potentials into a single threat value.

NASA can't pay for a killer asteroid hunt cost to find 90% of asteroids, comets (larger than 1km) would be about $1 billion

Apophis: Highest ever Torino scale (“4”)

• Initial calculation of 2.7% chance to hit the Earth in 2029. •Current calc = 1 in 12.3

million chance to hit the Earth in 2037.

Page 16: Mass Extinction

Holocene extinctionMan-made one?

•Most biologists view the present era as part of a mass extinction event, possibly one of the fastest ever•predict that humanity's

destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years.

Page 17: Mass Extinction

Late Heavy Bombardment

• short period (50-100 Myr) of bombardment much later than the formation of planet

Page 18: Mass Extinction

Sample Returns• Apollo Mission

• Six Apollo missions : 382 kg.• Three Luna missions : <

0.5kg.

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Moon Rocks

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Late Heavy Bombardment

LHB = lunar cataclysm = terminal cataclysm

Moon does not have plate-tectonics, so all rocks formed by various impacts should be concentrated on earlier ages!

• Proposed in 1973 by Tera et al. who noted a peak in radiometric ages of lunar samples ~4.0 - 3.8 Ga• Sharply declining basin-formation rate

between Imbrium (3.85 Ga) and final basin, Orientale (3.82 Ga)• Few rock ages, and no impact melt

ages prior to 3.9 Ga (Nectaris age)

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Proposed Dynamical Origins for LHB

• Outer solar system planetesimals from late-forming Uranus/Neptune (Wetherill 1975)

• Break-up of large asteroid (but big enough asteroids difficult to destroy)• Expulsion of a 5th terrestrial planet (Chambers & Lissauer 2002; Levison

2002)• Outer Solar System planetesimals & asteroids perturbed by sudden

expulsion of Uranus & Neptune from between Jupiter & Saturn (Levison et al. 2001)

• Late-stage post Moon-formation Earth/Moon-specific LHB (Ryder 1990)

dynamical readjustment of planets in a planetary system can “shakes up” remnant small-body populations…

could occur late, even very late.

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Clearing of Remnants Late Heavy Bombardment

Gom

es e

t al.

(200

5, N

atur

e)

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LHB effects on the Earth

• Extrapolating from lunar craters (and the size difference b/w Earth and Moon), the Earth must have experienced…

22,000 or more impact craters with diameters > 20 kmabout 40 impact basins with diameters about 1000 km several impact basins with diameter about 5,000 km

Sterilizing impact : Impact on a planet which wipes out all life forms.Depends on the size and velocity of an impactor (about 200-

300 km diameter?)

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Sterilizing Impact simulationSimulation of a slow impact by a 500km size asteroid…http://www.youtube.com/watch?v=LlF8APEkh-E

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LHB Issues for Extra-Solar System Astrobiology

• It is plausible that similar, or even much more extreme, LHBs or VLHBs would affect planets in other systems.o any special planetary configuration to

promote/enhance LHBs?

• What range of bombardments foster life (exchanging materials, spurring evolutionary change)?

• How big an LHB surely sterilizes a planet?

• Prevent or significantly delay a start of alien life

• Does all stars go through the LHB phase?

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Evidence of LHBs at other stars?

BD+20 307 (Song et al. 2005, Nature)

• 1-2 billion year old Sun-like star about 300 Light years away• million times more dust particles than the current Solar System• Even 100 times higher impact rate than Solar System LHB…

Page 27: Mass Extinction

In summary…

Important Concepts• History of mass extinctions• Causes of mass extinctions• Late Heavy Bombardment and its

implication to astrobiology• Dynamical instability of planets

Important Terms• Mass extinction• K-T impact (Chicxulub Impact)• Torino scale• Late Heavy Bombardment• Sterilizing impact

Chapter/sections covered in this lecture : 4.6, 6.4, 11.3Extreme Life Forms: next class!!