The document details various types of meteorites, including stony meteorites (chondrites and achondrites), iron meteorites, and stony-iron meteorites, highlighting their composition and origins. It discusses the significance of the Chixculub impact and its connection to the Cretaceous-Tertiary extinction event, noting the evidence of iridium from meteorites. Additionally, it lists major impact craters around the world, emphasizing the prevalence of such geological features.

1. METEORITES

2. Meteorite Types
– Stony meteorites
• Chondrites
• Achondrites
– Iron meteorites
– Stony-iron meteorites
• Pallasites
• Mesosiderites

3. Chondrites
• Stony meteorites – most common meteorites and
represent the oldest solids that are the building
blocks of the solar system
• Parent bodies were small-medium asteroids
• Contain up to 80% chondrules, which were freely
floating molten drops in space
• Chondrules are few mm to 1
cm spheres
• Mostly olivine and pyroxene,
with minor feldspathic glass,
troilite (FeS), chromite,
phosphates

4. Chondrite groups
• Ordinary chondrites – make up 80% of the
meteorites and 90% of chondritic meteorites,
abundant chondrules
• Carbonaceous chondrites –less the 5% of
chondritic meteorites, few chondrules, more
lithophile elements (Ca, Mg, K, Cr, Al, Cl,…), water
and organic compounds
• Enstatite Chondrites – 2% of chondritic
meteorites, enstatite-rich chondrules and abundant
metal and sulfide minerals

5. Peekskill Meteorite
Peekskill Meteor: October 9, 1992, a 12-kg meteorite struck a car in
New York.

6. Achondrites
• Similar to terrestrial basalts, represent 8% of
meteorites grouped
• Many such meteorites originating from one
asteroid
• Also includes Martian and lunar meteorites
Lunar Meteorite Allan Hills 81005

7. Iron Meteorites
• 5% of meteorites, all of largest meteorites (up to 66
tons)
• Composed of iron-nickel alloy intergrowths:
– Kamacite – Fe-Ni alloy at 90:10
– Taenite – Fe-Ni alloy at 80:20 to 45:65
Kamacite

8. Stony-iron Meteorites
• Mix of iron-nickel alloy and silicate
minerals (mostly olivine), 1% of meteorites
– Pallasites are thought to form core-mantle
boundary of differentiated asteroids
– Mesosiderite – equal parts metal alloy and
silicate with a breccia texture
Mesosiderite
Pallasite

9. Chicxulub asteroid/comet (~10-15 km) impact
(K-T boundary) (crator diameter ~ 180 km)

10. Cretaceous-Tertiary extinction (K-T extinction)

11. Dinosaur fossils
in lower rock
layers
No dinosaur
fossils in these
rock layers
Thin layer
containing iridium
from impactor

12. Iridium - evidence of an impact
• Iridium is very rare in Earth surface rocks
but often found in meteorites.
• Luis and Walter Alvarez found a worldwide
layer containing iridium, laid down 65
million years ago.

13. Comet or
asteroid about
10km in
diameter
approaches
Earth

18. An iridium-rich
sediment layer and
an impact crater on
the Mexican coast
65 million years
ago.
shows that a large
impact occurred
at the time the
dinosaurs died out,

19. Barringer Meteor Crater (~1 km diameter), Arizona,
formed from Canyon Diable Meteorite

20. Impact Craters
Clearwater lakes, Quebec –
36+26km diameter, 290
ma
• Many famous impact craters,
hundreds known on earth
(why might there have been
plenty more??)
– Sudbury, Ontario (250km
diameter, 1.85 ga)
– Chesapeake Bay (90km
diameter, 35 ma)
– Manson, Iowa (35km, 74ma)
– Barringer, Arizona (1.2km, 49
ka)
– Serpent Mound, Ohio (8km,
320 ma)

21. Quartz Polymorphs
• Coesite and Stishovite found associated with
impact craters