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Meteorite impacts

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Meteorite impacts

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    1. Meteorite impacts

    3. Direct observations of meteorite impacts Tunguska, Siberia, 30 June 1908…a big bang above the Earth’s surface Shoemaker-Levy 9, July 1994…impacts hitting Jupiter

    4. Direct observations of meteorite impacts In 1954, a 5-kg meteorite crashed through a house in Alabama the object bounced off a radio and hit the owner in the head

    5. Effects upon children

    6. Indirect evidence of meteorite impacts Preserved craters on the continents, mainly the oldest parts (shields) Lac cratére in northern Québec is a simple crater… …its rim diameter is 3.4 km, it is 250 m deep, and it is 1.4 Ma in age

    9. Meteor crater in Arizona is another simple crater showing rim ejecta

    10. Manicouagan The Manicouagan crater in Québec is a spectacular example of a complex crater Its original rim has been removed by erosion…the current diameter is 100 km It has an uplifted central core and outer rings, which are filled by a lake Its age - 210 Ma - coincides approximately with a large extinction at the end of the Triassic period

    13. Some definitions Meteoroid: matter revolving around the Sun or any object in planetary space too small to be called an asteroid or a comet Meteorite: a meteoroid which reaches the surface of the Earth without being vaporized Meteorites come from larger parent bodies within our solar system

    14. Asteroids Asteroids are rocky fragments which either: failed to consolidate into a planet, or represent remnants of a fragmented planet

    15. Asteroids and the Asteroid Belt The Asteroid Belt lies between Mars and Jupiter…there are about 4,000 objects As asteroids collide with one another, they fragment and send pieces into near-Earth orbits

    16. Types of meteorites derived from asteroids Asteroids have a metallic core and stony silicate mantle As asteroids fragment, both metallic and silicate pieces are produced

    17. Stony meteorites (94% of all meteorites) Two types: Chondites…contain chondrules…they are very old and primitive Achondrites…no chondrules

    18. Iron meteorites These consist of nearly pure metallic nickel and iron This photo shows an iron meteorite named ARISPE

    19. Stony-iron meteorites These are a mixture of the previous two types Often they are fragmental, suggestive of violent processes This stony-iron meteorite is named ESTHER

    20. Comets Comets come from the far reaches of the Solar System They have highly elongate, elliptical orbits which bring them close to the Sun They mainly consist of ice and dust, thus are referred to as “dirty icebergs” or “dirty snowballs” They are held together very loosely

    22. Impact events 1. Probabilities 2. Nature of the event 3. Consequences 4. Mitigation

    23. 1. Probabilities of a collision What are the chances of a large meteorite hitting Earth? As of 2003, ~700 objects with diameters > 1 km known to have orbits which intersect that of Earth And 30 new objects are discovered each year, with the search only 8% complete!

    24. Probabilities - Zebrowski Zebrowski shows that, on average, collisions of 1 km-diameter objects occur every 250,000 years Such an impact is sufficient to wipe out most of the human population

    25. Probabilities - Courtillot Is Zebrowski’s estimate too high? Courtillot suggests it is about 1 Ma between events In any case, you can see that these events are both very rare and very destructive

    26. Zebrowski vs. Courtillot The differences we see on the two graphs give you some idea of the uncertainties involved

    27. 2. Nature of the event Impact cratering is an important process in the history of Earth and other planets 107 to 109 kg of meteoritic flux strikes Earth each year, mostly in the form of dust

    28. Impact events The cratering process is very rapid Since the objects travel so fast (4-40 km/second), a huge amount of energy is transferred upon impact

    29. Cratering A blanket of ejecta is dispersed around the crater rock is fractured, crushed, and broken In large impact events, the rock can even be vaporized (depending on the type of rock)

    30. Cratering (continued) Very high pressures are reached, resulting in shock metamorphism (pressure-temperature increases) After the initial compression comes decompression, which may cause the rock to melt

    35. Consequences of a large impact event These would apply for an object of about 1 km or larger Actually, you may not want to hear the list of death and destruction (or maybe you do)...

    36. Consequences 1 A base surge, similar to a volcanic pyroclastic flow, will be generated by the impact For a terrestrial impact, rock will be pulverized and/or vaporized, sending up huge amounts of dust into the stratosphere

    37. Consequences 2 For an oceanic impact: huge amounts of water will be vaporized runaway hurricanes, called “hypercanes”, may be produced (winds to 1,000 km/hr?) Global tsunamis will be generated, which will ravage the Earth’s coastlines

    40. Consequences 3 In the short term, global wildfires will be generated by the impact event These fires will burn uncontrollably across the globe, sending more soot, dust, and gas into the stratosphere

    41. Consequences 4 All this suspended dust and soot will cause global winter and global darkness Acid rains will fall Crops will fail catastrophically The end result will be MASS EXTINCTIONS

    42. Consequences 5 One last interesting point: The impact likely will trigger devastating quakes around the globe, especially where tectonic stresses are high (i.e., plate margins) Volcanism (flood basalts) may occur on the opposite side of the globe from the impact, as a result of shock waves travelling through the center of the Earth

    44. Mitigation The problem is the possibility of little or no warning There are proposals to use nuclear weapons and satellites to “shoot down” or destroy such killer objects For further edification, rent “Armegeddon” from Blockbuster (1998) Good subject for a paper !

    45. Three case studies Tunguska 1908, Russia Shoemaker-Levy 9, July 1994, Jupiter The Cretaceous-Tertiary extinction, 65 Ma

    46. Tunguska, Russia, 30 June 1908 Something big seems to have exploded in the atmosphere The exact cause is uncertain, but we suspect a comet or a meteor

    47. What happened? The object’s entry appeared to be at an angle of 30-35° The object shattered in a series of explosions at about 8 km altitude

    48. Big fires In the central region, forests flashed to fires which burned for weeks a herd of 600-700 reindeer was incinerated

    49. Aligned trees Trees were felled in a radial sense About 2,000 km2 were flattened by the blasts

    50. What happened? Our best scientific guess is that it was part of a comet 20-60 meters in diameter… …no crater was found… …and no meteoritic debris has been found

    51. Area of devastation superimposed on a map or Rome. Yellow=charred trees; Green=felled trees The lack of a crater suggests disintegration above the surface of the Earth The lack of solid debris implies a comet rather than an asteroid

    52. A global view Soot from the fires circled the globe, producing spectacular sunrises and sunsets for months afterward The Tunguska event was the largest known comet/asteroid event in the history of civilization

    53. Comet P/Shoemaker-Levy 9, July 1994 This comet was first detected on 24 March 1993 It was broken apart by a close pass to Jupiter on 7 July 1992

    55. The sequence of events The collision of the comet with Jupiter occurred over several days, 16-22 July 1994 It was the first collision of 2 solar system bodies ever observed At least 20 fragments hit Jupiter at speeds of 60 km/second

    56. Sizes of fragments The largest fragments were about 2 km in diameter Huge plumes thousands of km high were generated Comparisons can be made with the Cretaceous-Tertiary extinction event

    58. Energies Fragment A struck with energy equivalent to 225,000 megatons of TNT, the plume rising to 1000 km Fragment G was the biggie, with 6,000,000 megatons TNT energy and a plume rising to 3,000 km Fragment G (and K, L) created dark impact sites whose diameters were at least that of Earth’s radius

    59. Fragment G This image shows a ring of hot gas about 33,000 km in diameter and expanding at 4 km/second from the impact of fragment G

    60. Fragment G impacting; observe four things: 1) thin dark ring: atmospheric shock wave from fragment explosion below cloud tops 2) dark streak within ring: path of fragment 3) broad oval feature: ejecta blanket 4) small black dot: impact site of fragment D a day earlier

    65. Impact events and mass extinctions In the Phanerozoic (570-0 Ma), there have been two great extinctions of fauna and flora: 1) end of the Permian Period at about 250 Ma 2) end of the Cretaceous Period at 65 Ma These extinctions serve to divide geologic time in the Phanerozoic into three main eras

    68. Some geologic reference points to put things in perspective Earth formed around 4,500 Ma ago Our ancestor Lucy lived about 3 Ma ago The last major glaciation occurred 0.01-0.02 Ma ago (10,000-20,000 years ago)

    69. The Cretaceous-Tertiary (K-T) extinction at 65 Ma End of the dinosaurs and other species In fact, about two-thirds of all species wiped out 80% of all individuals killed off Thereafter, mammals took over

    70. What caused the extinction? The two main theories are: (1) a meteorite impact (2) flood basalt volcanism Another idea is a hypercane sucking up and literally blowing away the dinosaurs

    71. Some important questions Was the extinction of the dinosaurs rapid or prolonged? Or both? In other words, prolonged followed by abrupt? Did a meteorite impact trigger volcanism? Note location of the Chicxulub crater to the Deccan basalts

    72. Was it a meteorite?

    73. Evidence for meteorite impact High iridium at the K-T boundary Unique to the K-T boundary? 9 parts per billion (ppb) Ir in clay at the boundary Background in area <<1 ppb Earth’s crust < 0.1 ppb Some metallic meteorites ~500 ppb

    74. Iridium and the dinosaurs The high iridium is coincident with the disappearance of the dinosaurs, as seen in the fossil record No dinosaur fossils above the K-T boundary, whereas there are lots below, as old as 165 Ma

    75. The iridium The iridium may have come from impact of a metallic meteorite Circulation and settling of Ir-rich dust would result in global distribution of Ir at the K-T boundary

    76. Global effects The atmospheric dust and gas from the impact event would cause global cooling (compare with nuclear winter) Global wildfires also would have been ignited by the fireball

    77. Other meteorite evidence Spherules…these represent melt droplets dispersed globally from the impact Shocked quartz…this requires high pressures

    78. The impact crater Located in the Yucatan Peninsula of Mexico, it is called Chicxulub It is completely buried, and was located by petroleum geologists The size of the crater implies a meteorite about 10 km in diameter

    81. Some incidental facts There are several localities in the Caribbean where tsunami deposits have been identified (interpreted) at the K-T boundary Many of the rocks associated with Chicxulub are evaporite sedimentary rocks (gypsum, anhydrite, etc.) containing sulfur (CaSO4) This sulfur may have been vaporized to produce sulfate aerosols in the atmosphere, contributing to global cooling

    83. Incidental facts (ctd.) Other rocks in the vicinity are limestones (CaCO3) Vaporization of evaporites and limestone would inject sulfur dioxide and carbon dioxide into the atmosphere Sulfur dioxide causes cooling, CO2 causes warming

    84. Climate change Short-term global cooling from: Dust from impact Soot from wildfires Injection of sulfur Longer-term global warming from: Injection of CO2

    85. Was it a volcanic eruption? One candidate are the Deccan Traps in western India These are huge outpourings of basaltic lava which are succesively stacked to more than 2,000 meters in places They form a kind of staircase, hence the word ‘trap’

    86. Flood basalt provinces

    87. Erupted volumes of basalt The Deccan represents about 1-2 x 106 km3 of lava By comparison, the Columbia River Basalt (CRB) is only 2 x 105 km3

    88. photos

    89. map

    90. Age of Deccan volcanism Interestingly, the Deccan Traps recently have been dated at 63-67 Ma And most of the volcanism occurred during a 500,000 year period at 65 Ma…which is the K-T boundary This is basically a geological instant in time

    91. The volcanic model The volcanic model basically is one of enormous fire fountains of basaltic magma into the stratosphere (at least 10-20 km high) Here is a small-scale version of this at Kilauea in Hawaii

    92. Gas emissions In subduction-related and caldera volcanism, lots of ash is produced But for basaltic eruptions, it is the gas, not the ash, which is significant In particular, large amounts of sulfur dioxide (SO2) can be liberated

    93. Short-term impacts If this gas is injected into the troposphere and stratosphere, the sulfur dioxide and other gases can have huge impacts The main short-term impact would be global winter conditions

    94. Tropospheric impacts Gases in the troposphere (0 to 10-20 km altitude) would be dissolved in water, generating highly acid rains These are basically rains of sulfuric acid (H2SO4) and hydrochloric acid (HCl)

    95. Stratospheric impacts SO2 injected into the stratosphere undergoes the following reaction: SO2 + 2H2O => H2SO4 + H2 The sulfuric acid forms very small particles called aerosols These effectively absorb UV radiation, and could decrease temperatures by up to 10°C

    98. A comparison: Laki, Iceland, 1783-1784 Laki is a basaltic volcano in Iceland, associated with spreading of the Mid-Atlantic Ridge The volcano erupted from 8 June 1783 to 7 February 1784

    100. Eruptive events at Laki A series of fissures opened, resulting in big eruptions Eruption columns reached 15 km altitude Fire fountains reached 800-1,400 m in height

    101. Volumes: Laki vs. Deccan A total of 14 km3 of lava was erupted (compare this with the 106 km3 from the Deccan) Large amounts of sulfur dioxide (SO2) were injected into the atmosphere Global cooling followed the eruption

    102. Impact of Laki Famine in Iceland: crop failures 50-80% of livestock died 25% of people died The winter of 1783-1784 was particularly harsh in Europe

    103. Longer-term impacts of large-scale basaltic volcanism The oceans become acidic, killing off algae and other marine life This “dead” ocean would be reflected by the clay (no fossils) at the K-T boundary, instead of limestone (shell accumulations)

    104. Longer-term impacts The acid oceans also dissolve calcium carbonate in the form of shells This results in release of CO2 from the oceans to the atmosphere The high atmospheric CO2 is a greenhouse gas, promoting global warming

    105. Some concluding remarks: meteorites vs. volcanoes Ir from a meteorite? From the Earth’s mantle via eruptions? The iridium anomaly is found not only at the K-T boundary, but also extends several meters on either side Has the Ir been redistributed from an originally thin layer at the K-T boundary? Or is it a record of more than a single event?

    106. Globally speaking... A meteorite impact into the Chicxulub region would produce: dust from the impact soot from global fires sulfur gases from evaporite rocks CO2 from limestone Basaltic volcanic eruptions would produce abundant sulfur, and probably CO2 also

    107. Points in favour of a meteorite High iridium global distribution of spherules global distribution of shocked quartz

    108. Points in favour of volcanic eruptions The ecological crisis began 105 years before the Ir-rich horizon… …and appeared to continue for a period of time afterward (~105 years?) Other mass extinctions appear to show some correlation with flood basalt events

    109. 5 major extinctions during the Phanerozoic (570-0 Ma) End Ordovician, 440 Ma end Devonian, 350 Ma end Permian, 250 Ma (Paleozoic-Mesozoic boundary) end Triassic, 200 Ma end Cretaceous, 65 Ma (K-T event) (Mesozoic-Cenozoic boundary)

    111. An interesting aside The K-T extinction is the only one for which there is good evidence for a meteorite impact

    112. End Permian extinction at 250 Ma: the big Daddy 90% of all species vanished Actually 2 brief, intense crises at 258 Ma, 250 Ma Correlates with age of Siberian Traps (flood basalts) in Russia at 250 Ma Interestingly: (a) no Ir anomaly; (b) no continental breakup

    113. Siberian Traps

    115. Flood basalts, mantle plumes, and continental breakup Beyond the correlation with extinctions, flood basalts also have important tectonic implications They appear to be the manifestation of the birth of hot spots And this birth frequently is sufficiently forceful to tear apart the continents

    116. A model of continental breakup A new mantle plume, which is hot and buoyant, pushes up a continent The doming causes thinning and fracturing of the crust The fractures allow rapid eruption of flood basalts from the head of the mantle plume

    118. Flood basalts and mantle plumes

    119. So flood basalts are fascinating phenomena Links with the geological timescale Links with faunal diversity (extinctions) Links with mantle plume birth Links with continental breakup

    120. In this context, the Deccan Traps are important The Deccan Traps represent the head of a mantle plume which was born at 65 Ma The volcanism led to the opening of a new Ocean (the Arabian Sea) Afterward, the plume’s head being emptied, its tail generated the track of the Reunion hot spot

    122. Meteorite impacts - readings Alvarez, W., 1997. T. Rex and the crater of doom. Princeton, Princeton University Press. Alvarez, L.W., W. Alvarez, F. Asaro, H. Michel, 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science, v. 208, pp. 1095-1108. Frankel, C., 1999. The end of the dinosaurs. Cambridge, Cambridge University Press. Grieve, R.A.F., 1990. Impact cratering on the Earth. Scientific American, v. 262, pp. 66-73.

    123. Meteorite impacts - web Two general sites of interest: http://neo.jpl.nasa.gov/neo/ http://www.nearearthobjects.co.uk/ Shoemaker-Levy: http://seds.lpl.arizona.edu/sl9/sl9.html Canadian sites on terrestrial impact craters: http://gsc.nrcan.gc.ca/meteor/index_e.php http://www.unb.ca/passc/ImpactDatabase/

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