Download lec22_28nov2007

What can meteorites tell us about the early S.S.?
Ge/Ay133
What kind of meteorites are there?
The systematic
collection of
meteorites from
Antarctica has
dramatically
increased the
number of samples
available.
Stony
Iron
Chondrite
types and
sample
chondrules:
Extinct radionuclines give assembled
time scales of 5-50 Myr. When is t=0?
Absolute dating error bars getting down to ~1 Myr!
From whence the complex nebular organics?
An amazing variety of organics are
found in chondrite matrices, esp. a
wide variety of aliphatic and
aromatic hydrocarbons, carboxylic
acids, amino acids, purines,
pyrimidines, and sugars. Synthesis?
dD values are large, structural diversity
complete. Supposedly formed by aqueous
alteration of ISM precursors on parent
bodies, but organic and silicate aqueous
signatures are contradictory. Can the
organics be made in the disk? The oxygen
fugacity is critical.
Geochem. Cosmochim. Acta 64, 329(2000)
L excess in Murray,
Murchison meteorites
(isovaline shown)?
How might you generate
such an excess?
Achnodrites:
No chondrules,
“planetary” processes.
Can find examples
from the Moon & Mars!
Johnstown Achondrite
Thin sections appear similar to
terrestrial basalts.
Iron Meteorites:
Widmanstätten crystallization patterns indicate slow cooling.
These irons and pallasites
likely originate in the cores
or core-mantle boundaries
of differentiated bodies.
Next time:
Core formation
& terrestrial
planets.