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the sizes of documented pairing groups in the Antarctic
collection to that point, suggesting a somewhat higher
number of ~5. Welten et al . [2011] used petrologic,
mineral chemical, and cosmogenic nuclide data to sug-
gest that nearly 2000 ordinary chondrites from Queen
Alexandra Range, roughly 60% of the total from that
area, are paired (Plate 9). This furthers the argument put
forth by Lindstrom and Score [1995] that pairing is dis-
tinctly nonlinear, with most meteorites paired with few or
any other meteorites, while a small number of pairing
groups dominate pairing statistics.
10,000
lnfalling Meteorites
s=-0.833
Yamato
n=5041
1,000
Queen Alexandra Range
n = 3442
Allan Hills
n=1502
Modern Stone Falls
Hughes (1981)
n=755
100
10.3.1. Mass Distribution
An alternative way to approach the examination of
meteorite statistics is to look at the cumulative mass dis-
tribution of a population relative to the number of actual
meteorites represented. Harvey and Cassidy [1989] and
Huss [1991] both point out that the mass of meteorites
found in Antarctic field sites (Allan Hills and Yamato)
peaks at ~10 g, while those of modern witnessed stone
falls peak at ~5 kg. This conclusion is logical in light of
the fact that small (<2 cm) meteorites are much easier to
spot on Antarctic ice than they are in non-Antarctic loca-
tions. Additionally, systematic collection of meteorites
in Antarctica and elsewhere (Roosevelt County, New
Mexico, for example, as discussed in Huss [1991]) recovers
more small meteorites than random searches for poten-
tial meteorite falls. Figure  10.5 shows a diagram from
Huss [1991, Figure 1] updated by Righter et al . [2006] that
shows the number of meteorites collected in these ice-
fields, Roosevelt County, and modern falls versus total
mass. If these meteorites were thoroughly examined and
put into pairing groups, the number of meteorites after
pairing would certainly decrease, though the mass of
many individual meteorites would rise. This would shift
the curves from each of the field sites shown in Figure 10.5
to the right (increased mass), making it more similar to
the Modern Stone Falls measured by Hughes [1981],
while also dropping the “number of meteorites” on the y
axis. In addition, if more of the small modern falls were
actually recovered [ Huss , 1991], the “modern falls” curve
would move up and to the left, as the number of meteor-
ites increased and the mass decreased.
10
Roosevelt Co.
n=152
.001
.01
.1
1
Mass (Kg)
10
100
1,000
Figure 10.5. Mass frequency diagram of icefields, Roosevelt
County, and modern falls vs. total mass (from Huss [1991],
modified by Righter et al. [2006] to include the QUE meteor-
ites). If the Antarctic meteorites were put into pairing groups,
the number of meteorites would decrease, with a corresponding
increase in individual mass. This would shift the curves from
each of the field sites to the right (increased mass), closer to
Modern Stone Falls, also reducing the number of meteorites.
specific field site where they are collected. The other 10%
of the population is dominated by carbonaceous chon-
drites, which make up 4% of all U.S. Antarctic meteorites,
and achondrites, with HED meteorites composing 2%.
To understand whether the U.S. Antarctic collection is
representative of material that fell to Earth over recent
history (terrestrial ages of Antarctic meteorites average
about 30 Ka, with the oldest around 2 Ma), it is reason-
able to compare broad statistics of the collection to other
similar collections. Here we choose modern observed
meteorite falls [ Grady et al ., 2000] and hot desert meteor-
ites from Northern Africa [ Welzenbach and McCoy , 2006,
McBride and Righter , 2010]. Both the modern falls
population and the hot desert meteorite population
sample more than 1000 meteorites, perhaps indicative
that they should also be a representative sampling.
At a broad level, it is noteworthy that the percentage
of  ordinary chondrites differs significantly between the
Antarctic population (~90%) and the falls and hot desert
meteorites (~80%) (Figure 10.6). It is also interesting that
while individual Antarctic sites demonstrate dramatic
variations in the relative abundances of H, L, and LL
chondrites, the cumulative populations of modern falls,
10.3.2. Does the Antarctic Population Represent
a Complete Sampling of Astromaterials?
An important aspect of the Antarctic population is the
fact that, as a whole, it contains 91% ordinary chondrites,
as shown by individual field sites that have produced over
1000 meteorites (Figure  10.6 and Table  10.3). This is
further evidence that the number of meteorites recovered
in a field area is the critical parameter in sampling a rep-
resentative assemblage of meteorites, far more so than the
 
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