Download Why Study Meteorites?

• Abundances of “elements” in solar system
– Clue comes from Meteorites (p.15-21) and
spectroscopic study on the Sun
Why Study Meteorites?
• State of early solar system
– Age of solar system
– Planetary formation procedure
– Chemical evolution in solar system
• Samples of other members (planets, asteroids,
comets etc) of solar system
– Chemical distribution of elements in solar system
– Information on the internal Earth
• Hazard for human and other species on Earth
How often do meteorites come to Earth?
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Where do meteorites come from?
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Asteroids
Comets
Mars
Moon
Types of Meteorites
• Interplanetary Dust Particles (IDPs)?
• Stony
– Consist of silicate minerals
• Iron
– Mostly metallic iron with up to 20% nickel
• Stony-iron
– Mixture of silicate and iron
• Lunar and Martian
1. Interplanetary Dust Particles
(IDPs)
irregularly-shaped IDP collected
in the atmosphere
Spherical IDP collected on the
ocean floor (300 μm across)
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2. Stony Meteorites
• Chondrites
– composed of silicate minerals
– contain chondrules: solidified droplets of solar
nebula
– unchanged since formation of solar system
• Achondrites
– Differentiated chondrites
– Igneous rocks
– include
• Martian meteorites (SNCO)
• Lunar meteorites
3. Iron Meteorites
• Probably represent cores of asteroids
• Most commonly found meteorites
• Widmanstätten patterns
Hoba Iron meteorite, Namibia
(largest known) 60 tons
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4. Stony-Iron Meteorites
• Mesosiderites-breccia of iron-nickel and
mantle rock formed by impact
• Pallasites-represent core-mantle
boundary of asteroid
5. Lunar meteorites (lunaites)
• 21 lunar meteorites are known. Youngest is 3.1Ga (youngest known
phase of flood volcanism on Moon). They are mostly basalt lavas
and anorthosite breccias
• They are very important because they may be samples from different
areas than sampled by the Apollo astronauts and the Soviet Luna
robots
Calcalong Creek meteorite, Australia
Lunar basalt. Note large plagioclase
feldspar crystals
6. Martian meteorites (SNCO)
S
N
C
O
SNCO Meteorites
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Analysis of gases (particularly noble gases) in fluid inclusions
in minerals is similar to Martian atmosphere, and suggests that
SNC meteorites are derived from Mars
A bit more on Chondrites
• The most abundant meteorite falls (~86 %)
• Very important in understanding early solar
system environment
• Contain Chondrules
Ordinary Chondrites
The Marlow, Oaklahoma, L4 chondrite exhibits sharply defined densely packed
chondrules. The chondrules vary greatly in size and shape, many being more
ellipsoidal than spherical. They are far from a close packed geometrical
arrangement, rather the arrangement here is chance packing.
(horizontal view = 15 mm)
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The Baszkowka L5 chondrite
fromPoland has 20% porosity. Note the
large voids in the interior. This meteorite
lacks the compaction of most chondrites.
This specimen measures about 8 cm in
the longest dimension
Bjurbole L/LL4 hand specimen. Its
extreme friability makes it subject to
crumbling. The chondrules frequently
fall out of the matrix leaving obvious
cavities. The specimen is 5.3 cm in
the largest dimension.
Building of Chondritic Parent
Body
Experienced
•Igneous (melting of chondritic precursor
followed by crystallization)
•Sedimentary (accretion of chondrules
and matrix material onto a growing
homogeneous body)
•Metamorphic processes (thermal
metamorphism occur creating
heterogeneous, layered structure)
Carbonaceous Chondrites
•The Allende meteorite (one of carbonaceous chondrites) is named for the town in
Mexico where it fell on February 8, 1969.
•One of the largest meteorites (total mass = 2 tons).
•It consists of large, irregularly shaped white inclusions (CAIs) and rounded chondrules
in a dark matrix. The inclusions are composed of minerals believed to have condensed
at high temperatures from a gas having the composition of the Sun, and their time of
formation is older than that of any other known solar system material.
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Carbonaceous Chondrites are
believed to be primitive!
Calcium-Aluminum rich Inclusions
(CAIs)
A 13.9 g slab of the Axtell CV3.0
chondrite showing a large (9 mm long)
CAI in the center.
A large (5.5 mm long) fine-grained CAI
from an Allende CV3 specimen.
•Composed of mainly Ca and Al
(minerals are highly refractory -> formed under high T
-> during early stage in solar system history)
•Allende contains abundant CAIs (5-10 vol %)
•The most primitive Solar System material!
Chronology of Early Solar Events
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Abundances of Elements in Solar system
Isotopes (2005)
Faure and Mensing
Key Observations
• extreme abundance of H and He (more
than 99% of all atoms)
• general decrease in abundance with
increasing Z
• relatively low abundance of some
elements (Li, Be, B, Sc) and relatively high
of others (Fe, Ni, Pb)
• greater abundance of even Z elements
compared to odd Z elements
How can we explain these features?
Geochemistry (1996)
Brownlow
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