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Mass Extinction
ASTR 1420
Lecture 9
Sections : 4.6, 6.4, 11.3
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Mass Extinctions in the Earth History
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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.
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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
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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.
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Causes • Sea-level falls (7 matches out of 12 cases)
destroy continental shelf area! disrupt weather pattern
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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
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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
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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
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Shoemaker-Levy
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Happens frequently…
• A chain of impact craterson 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.
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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.
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Late Heavy Bombardment
• short period (50-100 Myr) of bombardment much later than the formation of planet
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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 simulation
Simulation 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…
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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!!