Rbs*
7W
AG
,
DETERINATIO~
OR O
OARBONAOBOUS OHONDRITE
JIRRAYO.
by
IRNA B31ISR
B.S.,. The
ty Oollege of New York
(1961)
LLLUJt
SUBZTTSD IN PARTIAL PU
OF TUS 1QUIREMS*~S POR THE,
DSGRE
OF JASTR 0?
at the
OP
MISAOUSETTS INSTITU
TE01NoLoGY
January, 1964
Signature of Author ...
..
U
il4t44; ir.
Department of Geology and Geophl-es
Qertified
by *...*.fii4Ye..einr6. 67fiWi.
Aooepted by ......
.~
.
4....
....
Janury 20,1964
%w wW
7**
thsy RSupervisor
.. *******
#**1*#U, *,* e, 0
**
an ~~ate
**,.*
,,
8~tdents
_ I_ _~~_I__~_~_
Rb-Sr AGE DETRIMNATION OP
TIM
AiAOIAOJUSG-I HORTIT
"MURRAY"
J
by
ERA SISER
Sub itta
to the Department of Geology and Geophysts,
on January 20, 1964, in partial fulfillment of the requiresents
for the degree of Naster of Seienee.
The arbonacoeous chondrite Murray was analyz
by the
Rb-Sr method
fte age obtained was 4.9
0.19, x 10 yeare.
The de4y constant used was 1.8 x 100
yearel#.
This age
is within experimental error of the isohron determined for
Thus, type II carbonaceou ebhondrites
the stony m teorite.
are ooeonete with stony meteorites, they do not reprsent
primit ve material nor the outer layer of ann aste,g4a
parent body, The initial Sr itetopio ratio for r
used was 0.6980 ± 0.001.
Thesis Supervisor
itle
William R. ftnson Jr,
Assooiate Professor of Geology
TAZB
OP 10 MN
S
AbWtreat
2
Uist of Tables
4
List of ?iguns
5
Aoknowledge4ent0
6
Introdution
7
zperimental ProTAre
11
Sample Preparation
11
Ohenioal Prooodureea
12
Mase Spectromter TdehniquP
s
16
Onolusions
27
Appendix
2-8
iblography
30
-4-e
LIST OF TAM8
Table
~Page
20
1
Rb,and Sr Oontent of Mutray
2
Isotopic
Sposition of Murray
21
3
Iseotopia aomposition of Murray
22
4
RS an
23
5
Replicate Analyses of the SrO
6
Isotopi
o
Sr Blank Doten
Oopositiow of Murray
tandard
24
29
-5-
TABIOF PIRE
U
Plga.r
Pa~g
1
Isoehron of Pinson, et.al. (1963)
with data for "Murray* amperimposae4.
26,
2
Wo portions of Hass Spetrometer reoord.
27
AMEN
&8GIE
The work was carried out in
the Geochronology
Laboratory in the Department of Geology and Geophysics at
Kassachusetts Institute of Technology,
and was financially
supported by the U. S. Atomic Energy 0aomission and the
National Aeronautics and Space Administration.
The author
wishes to express appreciation and gratitude to Profeossrs
P. M. Hurley and W. H. Pinson, Jr. for financial support,
use of the facilities, enouragement and advice.
The author is
indebted to MIt
T; E. Krogh and Xr, R.H
MoNutt for endless hours spent in enoouragment,
assistane and
advice in the operation of the mass spectrometers,
would like to thank Mr. R
The author
M,. Shields for assistance in
perfecting the ohemioal procedure and Mr.
R. H. Roesman for
assistance and encouragnment during the course of the inveetigan
tion.
The author is
indebted to Dr. E.
P. Henderson of the
U. 8, National zuseum, Washington, D. 0. who supplied the
sample of Murray that was used in this investigation.
4 7
"
Carbona eous ohondri-tes contain more free earbon and
more water and sulphur than the ordinary ohondrites.
Their
bulk OaZhail aompsibetion, exOlusive of Volatiles and carbon
oompounds, is
simil4r to that of the ordinary ohondrites.
Wlik (1956) has olassified the oarbonaceous chondrites into
types I, IU, and iIX,
based on their oarbon, water, sulphur
and metalliQ iron oontents
8102
$go
0
tpe i
22.56
15.21
3.54
20.08
6.20
Type UI
27.57
19.18
2.46
13.35
3625
Type II
33.58
23.74
0.46
0.99
2.27
0
ttrther distintions between the three types can be
made on the basis of their known mineralogieo,
Type I
carbonaeous ohondrites oontain no apparent ohondrules.
They have low densities (rN 2.2) and oonsist mainly of an
amorphous, hydrous, layer-lattioe-sillioate (possibly chlorite
and/or serpentine), magnetite, magnetio spinel, water*soluble
sulphates, troilite, amorphous oarbon, complex hydrooarbons,
and free sulphur,
Type II carbonaceous chondrites more
olosely resemble ordinary chondrites in texture,
The
ehondrules consist chiefly of blivine and enstatite or
olinoentatite.
the chlorite-serpentine,
olivine, pyraQenes,
glass, troilite, and iron are imbed4ed in agundmass that is
opaque and amorphos .
2.9.
Type 11 densities range from 2.5 to
Much of the sulphur is in the free state.
earbon*oeous ohondrite
are olivine-pigeonite ohondrites.
They are similar to type II in texture.
range from 3.4 to 3.5.
auit. olinoenstatite,
ahlorite-serpentine,
glass.
type III
Their densities
Their main constituents are olivine,
opti
spinel, orthopyroxne,
troilite, plagioclase, iron, oarb
and
Type I and type I carbonaceous chondrites are
extremely friable, thus they are never found as large stones.
May theories on the origin of carbonaoeous ohoarites
exist.
Current theories all aseume that they are aeoumulations
of oosmic material that has been subjected to considerable
alteration, dispersed,
and possibly reaoumulated.
Urey (1961) proposed that earbonaceous ehondrites
ean not be the parent material of the chondritic meteorites
dueo
o the chemical composition differences within each group.
He postulates tmhat the earbonaoeous ehondrites belong to the
high iron group of ohondrites with the addition of hydrogen
sulphide, carbon compounds and water from outside sources.
Wood (1958, 1962) has postulated oxidation by G02
and later by 00.
114k (1956),
Rinxwood (1961), and Mason
(1960) hold the view that the oxidized, hydrated material of
the oarbonaceous ohondrites is primitive.
This primitive
material is hypothesized to have been altered to produce
-
9 -
olivine by a reduotion and dehydration process.
and Anders (1960) and Anders (1963),
Fish, Goles,
have postulated that
the asteroids are the parents of the meteorites and that the
oarbonaceous ohondrites represent the outer layer of this
parent body.
Patterson (1956) found an age of 4.55 ± 0.06 x 109
years for the Earth and meteorites from a study of Pb
isotopes.
Pinson, et.al. (1963) have shown, on the basis of
Rb-Sr analyses, thatanroyielding
an isochron yielding an age of 4.55 j
0.20 x 109 years (ARb = 1.38 x 10" 1 1 years
l
) can be
obtained from stony meteorites classified as *falls**
(1961, 1962) has published a similar result.
Gast
WThs represents
the time at which the chemical fraotionation of the meteorite
from the parent body took place.
Theshondrites apparently,
since they lie on an isoehron, have been closed systems with
respect to Rb and Sr since this initial chemical fractionation.
If the carbonaceous chondrites represent the primordial
material from which the stony meteorites were derived, the Rb8r age should be significantly greater than the 4.55 b.y. age
obtained from the meteorite isoohron and the Pb data.
A
significantly younger age should be obtained if the carbonacoeus ohandrites represent the outer layer of material of
an asteroidal body.
the carbonaceous ohondrites should lie
on the stony meteorite isoohron if
the carbonaoeous ahondrite
were formed at the same time and from the same parent body,
and thus would not be an anomalous group of objects, in
n10
w
that respect.
This investigatton ropresents an attempt at determin-
ing the Rb-Sr age of the Murray, Type II carbonaceous
chondrite.
Some of the conclusions reached by Pinson, etal.
(1963) were used in interpreting the data.
The investigation
was undertaken in orer to help shed some light. on the
theories of origin disnssed above.
BI
------I-------- ------- LILIC~I~--ILIII- .-X.~--e-LVL X-ULniY-IIII_-^_I-~-_r_~---_^~-*--- _
f 11h-
Eight pieoes of Murray totalling thirty five grams._
were taken for analysis.
Museum ntitber (# 1769).
Each contained a U.
S. National
The identifying arre
removed from each piece with a carboruntum grinding wheel
he surface. of each saple was then cleaned of dust and clay
with a wire rotating brush.
A stainless steel mortar and pestle and an agate
mortar and pestle were used to pulverize and fine-grind the
sample.
The stainless steel mortar and pestle were cleaned,
firs%on a Dumore grinder mounted on a lathe and then washed
with demineralized i'ter
and aestone.
The agate hand mortar
and pestle were cleaned with pumice, laboratory soap,
demineraliied water, 2N HOL, demineralized water and then
acetone.
An aluminum shield was made to fit over the agate
hand mortar to prevent loss while grinding.
Before grinding operations were begun, the entire
work surfaoe was covered with a clean sheet of parafilm,
The sample was coarsely broken up in the stainless steel
mortar.
he agate
Small amounts were then transferred to to
mortar where they were finely ground.
This finely ground
portion was transferred to a clean, screw cap vial for
storage.
One of the eight original fragments was preserved*
~__
- 12 -
Garbonaceouns ohondrites contain very small amounts
of Rb and Sr, these elements being in the range of 1 to 2
ppam
b, a'
10 to 12 ppm Or.
Thus, the contamination level
must be kept as low as possible.
various ethan es in
and
In order to aohi ve this,
the standard laboratory procedure (erzeog
itnson, 1956; Hersog, ets
al., 1958;
ture and tuarley,
1962) have been effected.
Waaserburg (1963) has shown that strontium Qontam4a-n
tion oocurs from the use of laboratory or pyre
glasoware.
This conta-ination is not picked up in the blank experiments
and seems to ocour only when miner l samples are used4
Seemingly it is the contact of te hot solution aontaining
the analysis sa ple with the glassware thnt oauses the 1eathb
ing out of the strontium.
Thus, the steps in whioh solutions
are evaporated or residues ignited, in pyrex beakers seem to
produce significant a~ ounts of conta ins' tion.
To eliminate
this sourxe of containation polyp opylene beakers have been
substituted for pyrex beakers,
Previously, the residue
obtained from the ion exohange colun was ignited in a 5 al
pyrex beaker,
Due to the possibility of contain
ntion at
these high temperntures, 5ml fused quartz orucibles, obtained
from the Thermal American Pused Quartz O-mpany, have been
u~i~SEed
Tyoor ion exchange aolumns were used in place of
pyrexs
Pused quartz wool was used to keep the ion exoba
resin confined in the bottom of the column.
Vyoor capillary
tips are used to place the prepared saple on the mass
spectrometer filament.
In fact, the use of pyrex glaseware
was entirely eliminated from the operation of preparing
samples for the mass 4etroometer.
In the dissolution proeeuadue,
water are used.
e water is
then vyeor distilled.
in vulor stills
used is
four typesa
of aoi
and
distilled, desineralised and
The HQ1 and 00
used are distilled
from reagent grade HO1 and HNK0.
The *X104
omeraly double distilled in rycor and shipped
in vyoor aMpules from the 0. frederiak Smith
QOmpany.
HE was purified by Robert X.
hemical
hielde by nsing a
polyethylene tubing and teflon bubbling apparatus with vyeor
distilled water#
30,5 N HP was prepared in this manner.
in the dissolution of the earbonaceous ehoadrite an
insoluble blaok residue is
formed,
this residue must be
separated before putting the solution on to the ion exobang
column.
The separation was affected by centrifuging at high
speed in a vyor centrifuge tube.
As a further precaution against oontamination, the
entire work area around the ion exchange columns was covered
with plastie sheeting.
An aluminum cover was put over the
hot platq and the inside covered with teflon tape.
umetoes experiments by other workers in
However,
the laboratory have
- 14 -
demonstrated that laboratory fallout oft
hband Sr is a
negliglble source of contaminatlon for these elements in
ohondrite analysis work.
One and a half to two gram samples were weighed out
on a Mettler balane and placed in platinum oruacibles.
small amount of water anw
A
6N 101 were added and the samples
were allowed to stand overnight.
It is thought that this
step aide in dissolution for the olivine is readily attaoked
by this acid.
E
Dilute Rb
J
le.
7
and Sr
6
were added by pipette to each
Extenstre calibration work has been done aon the
spike and shelf solutions
ratio is quite sensitive to
(P
on, 1962).'
The Rbp /8S86
hanes in the spike and shelf
solutions, and to a knowledge of the isotoplo eomposition of
these solutions.
After the addition of the spikes to each sample#
approximately 30 ml Hf and 3 ml
i0104 were added. The
samples are then plaoed on a steam bath, allowed to digsat
with frequent stirring by a teflon rod
When this portion
of' 1 has evaporated, another portion is added, and again
evaporated with constant stirring.
As perfect a solution as
possible was obtained by adding measured quantities of 2N 101
and water with constant stirring.
It is important to obtain
perfect equilibration between sample:
and spike, and it is
thought that this was attained from the clearness of the
solutions in each oase.
The sample is then removed from the
-.....~
steam bath and allowed to aool.
$r 8 5 and
ra ioaotive tracers were added.
fhe sample was then tr=naster*-
M
earier-fee,
red to voor centrifte tubao, and oentritlued for several
minatesa
The supematant was poured off and placed on the
ion exehange columns,
The
*ortn
2.5 am* by 60 e.
resin,
.eo hae
columns are approzimately
and are about half filled with Dowex 50&548
This is a strongly alotdieCation eo.xhw
&8 cross-li~
resin with
and a mesh size, of two to ftour hd r4ndt
The column was elated with 2N H,01 anA monitored with
a scintillation counter.
The Rb and $r fraotions were
collease
in 20 t20 30 ml portions in the 100 ml polypropylens
beakers.
?or both fb and Or, the beakers eentaining the
highest
cati vi
Wty4 and S85 were combine
evaporated
down and transferred to a 5 ml fused quartz cruiile
which
contained a fw mis of 0104*. The beakers were plaoed on a
hot plate, evaporated to dryness, and ignited oer
burner to remove the exOas
H010 4 .
a
-yrell
A few mla of
QHN10 were
then added and the beaker was again taken to dryness. This.
last: step was repeated.
The sample was then ready to be
placed on the mass spectrometer filament or to be stored for
future use.
Along with each group of isotope dilution analyses,
a set of Sr and Rh blanks were run.
treated in
these blank were
the same manner as the sample.
Por aS
isotope ratio analyses, a three gram sample
was veighed out.
The dissolution prooedure was the same
but no Rb or Sr spikes were added.
The mass spectrometer used was standard 6-inch
radius,
600 sector, solid source,
type machine.
single collector,
It was designed and built at 1I.
Nier
T.
the
ion ourrent was amplified by a vibrating reed seletrometer
and peake recorded on a Brown Strip Ohart Recorder,
the
low pressures necessary for operating were obtained by a
forepump in series with a mercury diffusion pump.
The
filament was tantalum ribbon that is spot welded to the posts
of the sourse.
All the filaments were proven clean of the
analysis element in the mass spectrometer, before applioation
of the sample.
The sample is placed on the filament by means of a
vycor capillary tip.
It
is put on in the form of a nitrate
and slowly evaporated to dryness.
-
The analytical results obtained in this thesis
investigtion are shown in Tables 1 - 6
MEpliaate Isotope,
dilution analyses were made for rubidium and strontluma
Rubidium and strontium blank determinations were made along
with the isotope dilution analyses.
The elemental content of Murray, on the basis of
triplioate analyses, are 1.67 + 0027 ppam R; 11405 ± 0.029
ppa Sr, the precision being expressed as the standard deiation
of the mean* These isotope dilution values have all been
correated for blank contamination, which in all' ass were
almost negligibly small, as shown in Table 4 The Rb/Sr
weigh- ratio was converted to Rb 87 /8r
A value for the isotopi
86
atoade ratio.
oomposition was determined
from a mass espotroaetrie run of 78 sets, and, by our
laboratory standards, was of the very highest quality.
portion of the mass speatrometric record is
Figure 2.
The value obtai
A
reproduced in
d.was 07249 + 0.0005.
Correcting this value for contwination, a value of 0.7250 ±
0,0005 was obtained, demonstrating again the near negligibility
of contamination.
On the basis of two mas
sets apiese,
spectrometria
aruns of 18
a value of 0.7254 + 0.002 was obtained,
Although
the runs were of poor quality, this value lies within
experimental error of the value obtained from the run of
high precision.
s-
18 -
the standard SrQ0~ (Rimer and Amend, Lot # 492327)
was used as an interlaboratory standard and to test the
preotaton of the
meteorite.
sotope ratio determinations for the Murray
A value of ( 8r 6 /r
8
) ranging from 0.708 to
0,709 is repotted by Paurv and Hurley, 1963; and Pinson, etal. 19634
This standard was run during the oourse of the
Murray Sr isotope ratio analyses, with the results shown in
Table
.
These values were well within the values reported
by several other laboratories.
The S6/8r87 ratios were corrected for
sotopia,
fraotionation by assuming that the Sr86 /8r 8 ratio is a
constant and equa1 to 0.1194.
The normaliation of the Sr6/
Sr'7 ratio is achieved by applying half of the fator
noesesary to adjust the Sr&E/Sr
Sr87 /886 ratio.
8
ratio to 0, 1194 to the
This normalization procedure has been
adequately justified by Paure (1961), and Yaure andUurley
fthe age formula for the Rb-Sr method Itt
8
Where (s~r
8 6
the age;
is the decay constant for iP.
)p is present, measured ratio; (r87T/S$W6)
is the initial ratio; (fRBS/886) is the atomie ratio; t is
A1drteh (1950)
reported a half-life for Rb87 of 50 + 2 x 109 years;
ew ll
*
al 405 bw,y for
Anoo
CNA4-i
Zo1--14
wxi tlerta
of
i1w1
m, 1 93tr
±049zZ
an
zzs
vootna
a
- 20 -
TADbZ
'b
1.70
1,62
I
ar
11.01
0.4455
10.99
0.4487
11.08
0.4241
0,4394
1.67
S(of the mean)
E (of tas moan)
z0.027T
. .5
.lam++
Rb T/Srs
*0tf9
$.ts1~
$ 40077
- 21 -
IbotEoria Weapositin at
rray
sr"Y/asrp&
_fPl~i~h~E~3.
(Aormllzodll
,CI~B~lgsSL~SaMU~c).
(e4~5 orstfr.Mr
M
041194
0.7949
04244
0.72O
E(oe t owns)
t a
(6V
ta.td
430
Yt
1
- 14a02WU ynnr)
4aahnL
x 40 yea*
XA
.
p.0$
** 22aww
ZaotopS a #0 o~o~tton of Wt ny
0.1180
0 q7256
0*706
0,0730#
0170
0.7282
0*1253
6. Q2KC1"
19.0ulr45"
4
00090
0.24
1404,00
OvU84B
0
for or
O*26
mZ3 -
1&SBLS 4
0*026'
0.071
- 24 -
ASpth
Sepliate Analyses of the Sr3"
B5
Standsrd
&4..2A) Lot
(3wAr
86/88
87/86
07/84
0.1186
0.7105
0.7080
0.1202
0.7060
0.7083
0.1191
0.7094
0.7084
0,1179
0.7119
0.7074
0.760
*H
c+ O
0.750
9a
No
P* 0
0
(D
0.740
ao
0
U)
0.730
SCD
3c*
0.720CD
CfD
0.7 10
CD
0
0.700
0.690
0.0
0.2
0.4
Rb 8/S
0.6
r86
0.8
1.0
- 26 -
Figure 2
Two portions of Mass Spectrometer record,
for Murray unspiked Sr analysis.
The age of 450 + 0.19 x 109 years obtained for tbhe
oarbonaceous ohondrite Murray indicates that Type II
carbonaceous ohondrites appear to be cogeneti
with stony
meteorites - i.e., they lie within experimental error of the
isoohrons reported by Gast (1961, 1962) and Pinson, et. al.
(1963).
The isoohron of Pinson, et. al. is reproduced in
Figure I with the data for 4urray superimposed on it.
Within the error limits assigned to the age of Murray,
and 2inson's isoehron, the hypothesis that carbonaceous
chondrites represent the outer layer (which differentiated
at a later date) of a parent asteroidal body (DufPesne and
Aners, 1961; Anders, 1963) remains a possibility.
At the present status of this work, and because of
the possibility of further refining the stony meteorite
isoohron, the hypothesis that the carbonaceous ehondrites
are the primitive material frm which the stony meteorites
are derived, is still a poseibility.
However, comparing the Rb-Sr age of 4.30 ± 0.19x10 9
years with Patterson's Pb age of 4.55
± 0,06z10
9
years, it
seems highly unlikely that the Type II carbonaceous ohondrites,
such as Murray, are older.
Thus, the Rb-Sr is rather strong
evidence that the Type II carbonaceous chondrites are not the
primitive material from which the stony meteorites were derived,
* 28
-
Values of 0.7204 and 0.7192 were caloulatod from two
of the isotope dilution analysee (Table 6).
Sr86 ratio of 0.C980 (Pinson,
An initial Sr87/
a
at,
1963) was assumed.
These
ealoulatihns were made to serve as an estimate of what the
measured isotopio composition would be.
The ealculated value
would have more significanoe if a Sr 8 4 spike had been used in
addition to a $t8
spike, thus enabling a correction for
instrumental fractionation to be made.
In addition, the use
of the above initial Sr 7/8 7rf ratio is unjustified if the
carbonaceous ohondrites do not lie on the isoohron obtained
from the stony meteorites.
In calculating the age of the
carbonaceous ohondrite, only the value obtained from the
unspiked mass spectrometer runs was used.
-* 29 -
?ABLA ~6
Isotopic
1easta4
Io
omposition of Murray
I4in
Xolasmman
A1na0D0tP
0.3286
0.3301
0.1086
0.7204
34
0.3385
0.2960
0.1150
0.17192
96
AsnAed
a
78st initial ratio a 04980
- 30 -
Aldrich, L. T., Wethgill, G W., and Tilton, G. R., (1956),
Half-life of Rb,.
ifhyl,
wL.
2 1045-1046.
Anders, S., and (oles, S. Q, (1961), Theories of the origin
, 4du.
fl, 58-66.
of meteorites. 9.i
Anders, E., (1962) On the origin of oarbonomeous chondrites.
Enrioo Permi anstitute for Nualear Studies # 62217.
Anders, E., (1963), Meteorites and the early history of the
solar system. Prooeedings of the Obnfarenoe on the
Origin of the Solar System, ed. by Jastrow and Gameron,
Academie Press N.Y.,
N.Y.95-104.
Dufesne, *. R., and Anders, E., (1962), On the chemical
evolution of the earbonaoeous chondrites. oeouxg:A4t
GOesesQv. A4t4 g2, 1085-1114.
E. (1963), tihemical Evolution
. R., and Ander-,
Du reene,
of the carbonaceoue ahondrites. ehap. 14, The Moon,
Meteorites and Comets, IT The Solar System, ed.
Middlehurst, B. M., and Kuiper, G. P., Univ. Chi. Preass,
Chio., Ill.
Farrington, 0i 0. (1915), Meteorites, their structure, oomposition, and terrestrial relations. PUble by the author.
Paure, G., (1961) The Sr87 / Sr86 ratio in Continental and
Oceanic asalts and the Origin of Igneous Ro ks, PhD
thesis at Massachusetts Institute of technology*
Paure, G., and Hurley
P. M., (196), The isotopic- compo-
sition of strontium in oceanic and continental basaltes
,_erOl.
application to the origin of igneous rocks.
4, 31-50.
rItA*, Ooles
1Pi,
4, G. and Anders, Ea., (1960)
in the meteorites $
in asteroidal bodies,
flynn, K4 P., and
TMe record
4
On the development
meteorites
AsOtrgzwhy
As U* 245-258.
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