Meteorite impacts Comparative energies No human in

Meteorite impacts

Comparative energies No human in past 1, 000 years has been killed by a meteorite

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

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

Effects upon children

Indirect evidence of meteorite impacts z. Preserved craters on the continents, mainly the oldest parts (shields) z. Lac cratére in northern Québec is a simple crater… z…its rim diameter is 3. 4 km, it is 250 m deep, and it is 1. 4 Ma in age

Location map of some impact craters seen at the surface

Lac cratère

Meteor crater in Arizona is another simple crater showing rim ejecta

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

Manicouagan St. Lawrence River

Central uplift

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

Asteroids z. Asteroids are rocky fragments (diameter 10 m to 1000 km) which either: zfailed to consolidate into a planet, or zrepresent remnants of a fragmented planet

Asteroids z. Metallic: some stony types are strong and hard and may hit the Earth. z. Weak, friable types likely will explode in the atmosphere at high altitudes.

Comets z Comets come from the far reaches of the Solar System (outer solar system, kuiper Belt and in the Oort Cloud). z They mainly consist of frozen water, carbon dioxide, or both with admixed small rock fragments and dust, thus are referred to as “dirty icebergs” or “dirty snowballs” z They have highly elongate, elliptical orbits which bring them close to the Sun

Comets z. The tail of the comet is produced as ices melt and gases and dust particles are shed from the object. z. Generally explode in the atmosphere at high altitudes.

Comet West, 9 March 1976

Comet P/Shoemaker-Levy 9, July 1994 z This comet was first detected on 24 March 1993 z It was broken apart by a close pass to Jupiter on 7 July 1992 Hubble image, 1 July 1993

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

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

Other definitions z. Meteor: light through the sky. Most meteors are destroyed in Earth’s atmosphere. z. Meteoroid: matter revolving around the Sun or any object in planetary space too small to be called an asteroid or a comet z. Meteorite: a meteoroid which reaches the surface of the Earth without being vaporized

Stony meteorites (94% of all meteorites) z Two types: z Chondrites…contain chondrules…they are very old and primitive z Achondrites…no chondrules Photo of a carbonaceous chondrite (carbon-bearing)

Types of meteorites derived from asteroids z Achondrites have a metallic core and stony silicate mantle Metallic core z As asteroids fragment, both metallic and silicate pieces are produced Stony silicate mantle

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

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

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

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

Probabilities - Zebrowski z Zebrowski shows that, on average, collisions of 1 kmdiameter objects occur every 250, 000 years z Such an impact is sufficient to wipe out most of the human population From Zebrowski (1997)

Probabilities - Courtillot z Is Zebrowski’s estimate too high? Courtillot suggests it is about 1 Ma between events z In any case, you can see that these events are both very rare and very destructive From Courtillot (1999)

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

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

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

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

Broken rock Ejecta blanket fracturing Simple craters are basically simple bowls With time, the ejecta blanket outside the crater is eroded

melt Central uplift Complex craters are generated by rebound of the central core This core, as it decompresses, may melt

There about 200 large, well-preserved impact craters worldwide…BUT…>>200 impact events during Earth’s history This map shows both SURFACE and SUB-SURFACE examples

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

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

Consequences 2 z. For an oceanic impact: zhuge amounts of water will be vaporized z. Global tsunamis will be generated, which will ravage the Earth’s coastlines

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

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

Consequences 5 z. One last interesting point: z. The impact likely will trigger devastating quakes around the globe, especially where tectonic stresses are high (i. e. , plate margins) z. 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

From Murck et al. (1996)

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

Two case studies z. Tunguska 1908, Russia z. The Cretaceous-Tertiary extinction, 65 Ma

Tunguska, Russia, 30 June 1908 z Something big seems to have exploded in the atmosphere z The exact cause is uncertain, but we suspect a comet or a meteor Aerial view of Tunguska Natural Reserve

What happened? z The object’s entry appeared to be at an angle of 30 -35° z The object shattered in a series of explosions at about 8 km altitude Tree blowdown from the explosions; Note parallel alignment of the trees

Big fires z In the central region, forests flashed to fires which burned for weeks z a herd of 600700 reindeer was incinerated

Aligned trees z Trees were felled in a radial sense z About 2, 000 km 2 were flattened by the blasts

What happened? z Our best scientific guess is that it was part of a comet 20 -60 meters in diameter… z …no crater was found… z …and no meteoritic debris has been found Felled trees aligned parallel to each other

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

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

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

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

What caused the extinction? z. The two main theories are: y(1) a meteorite impact y(2) flood basalt volcanism

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

Was it a meteorite?

Evidence for meteorite impact z. High iridium at the K-T boundary z. Unique to the K-T boundary? z 9 parts per billion (ppb) Ir in clay at the boundary z. Background in area <<1 ppb z. Earth’s crust < 0. 1 ppb z. Some metallic meteorites ~500 ppb

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

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

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

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

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

Chicxulub crater Approx 300 km

Some incidental facts z Many of the rocks associated with Chicxulub are evaporite sedimentary rocks (gypsum, anhydrite, etc. ) containing sulfur (Ca. SO 4) z This sulfur may have been vaporized to produce sulfate aerosols in the atmosphere, contributing to global cooling

Incidental facts (ctd. ) z. Other rocks in the vicinity are limestones (Ca. CO 3) z. Vaporization of evaporites and limestone would inject sulfur dioxide and carbon dioxide into the atmosphere z. Sulfur dioxide causes cooling, CO 2 causes warming

Climate change z. Short-term global cooling from: y. Dust from impact y. Soot from wildfires y. Injection of sulfur z. Longer-term global warming from: y. Injection of CO 2

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

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

Globally speaking. . . z. A meteorite impact into the Chicxulub region would produce: ydust from the impact ysoot from global fires ysulfur gases from evaporite rocks y. CO 2 from limestone z. Basaltic volcanic eruptions would produce abundant sulfur, and probably CO 2 also

Points in favour of a meteorite z. High iridium zglobal distribution of spherules zglobal distribution of shocked quartz

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

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

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

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

Meteorite impacts - web z Two general sites of interest: y http: //neo. jpl. nasa. gov/neo/ y http: //www. nearearthobjects. co. uk/ z Shoemaker-Levy: y http: //seds. lpl. arizona. edu/sl 9. html z Canadian sites on terrestrial impact craters: y http: //gsc. nrcan. gc. ca/meteor/index_e. php y http: //www. unb. ca/passc/Impact. Database/