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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/
