mass extinction astr 1420 lecture 9 sections : 4.6, 6.4, 11.3

Mass Extinction

ASTR 1420

Lecture 9

Sections : 4.6, 6.4, 11.3

Mass Extinctions in the Earth History

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.

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

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.

What’s the cause? Temperature?

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

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

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.

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

destroy continental shelf area! disrupt weather pattern

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

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

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

Shoemaker-Levy

Happens frequently…

• A chain of impact craterson Ganymede

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.

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.

Late Heavy Bombardment

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

Sample Returns• Apollo Mission

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

0.5kg.

Moon Rocks

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)

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.

Clearing of Remnants Late Heavy Bombardment

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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?)

Sterilizing Impact simulation

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

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?

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…

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!!