1. Research Articles
using the instrument suite aboard the
Curiosity rover exploring Gale crater.
Geologic Setting
Gale is a ~150 km diameter impact
crater that formed near the Late Noachian - Early Hesperian boundary (5,
K. A. Farley,1* C. Malespin,2 P. Mahaffy,2 J. P. Grotzinger,1 P. M.
6), or around 3.7-3.5 Ga according to
Vasconcelos,3 R. E. Milliken,4 M. Malin,5 K. S. Edgett,5 A. A. Pavlov,2 impact crater models (3, 7). In addition
to the ~5 km high central mountain of
J. A. Hurowitz,6 J. A. Grant,7 H. B. Miller,1 R. Arvidson,8 L. Beegle,9
stratified rock informally known as Mt.
9
2
10
2
F. Calef, P. G. Conrad, W. E. Dietrich, J. Eigenbrode, R.
Sharp, the crater is partially filled with
Gellert,11 S. Gupta,12 V. Hamilton,13 D. M. Hassler,13 K.W. Lewis,14 S. sedimentary rocks derived from the
crater rim. Crater density distributions
M. McLennan,6 D. Ming,15 R. Navarro-González,16 S. P.
imply a somewhat younger age (Early
17
18
1
19
Schwenzer, A. Steele, E. M. Stolper, D. Y. Sumner, D.
to Late Hesperian, or ~3.5-2.9 Ga) for
at least some of these deposits (5, 6).
Vaniman,20 A. Vasavada,9 K. Williford,9 R. F. WimmerWhile heading for its destination at Mt.
Schweingruber,21 and the MSL Science Team†
Sharp, Curiosity traversed a gently
1
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125,
sloping plain where local outcrops of
USA. 2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. 3School of Earth Sciences,
pebble conglomerate were encountered,
4
University of Queensland, Brisbane, Queensland, QLD 4072, Australia. Department of Geological
recording the presence of an ancient
5
Sciences, Brown University, Providence, RI 02912, USA. Malin Space Science Systems, San Diego, CA
stream bed (8). Most of this surface is
6
7
92121, USA. Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA. Center
heavily cratered and covered with rock
for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at
and soil (Fig. 1). However, a substantial
Independence SW, Washington, DC 20560, USA. 8Department of Earth and Planetary Sciences,
expanse of bare bedrock was encounWashington University in St. Louis, St. Louis, MO, 63130, USA. 9Jet Propulsion Laboratory, California
Institute of Technology, Pasadena, CA 91109, USA. 10Earth and Planetary Science Department, University
tered in an ~5 m deep topographic
of California, Berkeley, CA 94720, USA. 11Department of Physics, University of Guelph, Guelph, ON N1G
trough (Yellowknife Bay) representing
12
2W1, Canada. Department of Earth Science and Engineering, Imperial College London, London SW7
an erosional window through a se2AZ, UK. 13Southwest Research Institute, Boulder, CO 80302, USA. 14Department of Geosciences,
quence of stratified rocks known as the
15
Princeton University, Princeton, NJ 08544, USA. NASA Johnson Space Center, Houston, TX 77058, USA.
Yellowknife Bay formation (Fig. S1
16
Universidad Nacional Autonoma de Mexico, Coyoacan, Mexico City 4510, Mexico. 17Department of
18
and (9)). These rocks consist mostly of
Physical Sciences, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK. Carnegie Institution, Geophysical
distal alluvial fan and lacustrine facies
Laboratory, Washington, DC 20015, USA. 19Department of Geology, University of California, Davis, CA
of basaltic bulk composition and were
95616, USA. 20Planetary Science Institute, Tucson, AZ 85719, USA. 21University of Kiel, Kiel D-24098,
Germany.
derived from the crater rim (9, 10).
Compared to adjacent geological units,
*Corresponding author. E-mail: farley@gps.caltech.edu
the Yellowknife Bay trough is notable
†MSL Science Team authors and affiliations are listed in the supplementary materials.
for its lack of visible craters and its
apparently greater degree of stripping
We determined radiogenic and cosmogenic noble gases in a mudstone on the floor
of impact ejecta and wind-blown soil.
of Gale crater. A K-Ar age of 4.21 ± 0.35 Ga represents a mixture of detrital and
This appearance suggests active eroauthigenic components, and confirms the expected antiquity of rocks comprising
sion, distinctly different from the adjathe crater rim. Cosmic-ray-produced 3He, 21Ne, and 36Ar yield concordant surface
cent map units (9). However, the
exposure ages of 78 ± 30 Ma. Surface exposure occurred mainly in the present
depositional age of the Yellowknife
geomorphic setting rather than during primary erosion and transport. Our
Bay formation, its stratigraphic relaobservations are consistent with mudstone deposition shortly after the Gale impact,
tionship to the adjacent alluvial fan and
or possibly in a later event of rapid erosion and deposition. The mudstone remained
to the strata of Mt. Sharp, and the causburied until recent exposure by wind-driven scarp retreat. Sedimentary rocks
es and timing of its exposure are all
exposed by this mechanism may thus offer the best potential for organic biomarker
presently uncertain.
preservation against destruction by cosmic radiation.
As shown in Fig. 1, the Sheepbed
mudstone and stratigraphically overlying Gillespie Lake sandstone of the
Multiple orbiter and rover missions have documented a rich geologic
Yellowknife Bay formation (9) form a rock couplet of apparently variarecord on the surface of Mars, likely spanning almost the entire history
ble rock hardness, and their contact has eroded to form a decimeter-scale
of the planet (e.g., 1). However, interpretation of this record is impeded
topographic step. The Sheepbed-Gillespie Lake contact is sharp and
by our limited understanding of the connection between the materials
marked by scouring of the underlying mudstone, producing a small scarp
observed and their absolute age. Impact crater densities are the primary
and in some locations an overhang. Calved-off blocks of the sandstone
means for establishing a chronology for geologic features on Mars and
occur at the base and a few meters outboard of the scarp, but not beyond
other solar system bodies (2–4), but crater-based dating methods suffer
(see figure 3 of (9)). This suggests that residual fragments of the degradfrom multiple sources of uncertainty that obscure both absolute and relaing scarp are removed efficiently enough to leave only a very thin lag
tive ages. In contrast, on Earth, isotopic dating methods provide a powdeposit at locations where the Gillespie Lake member is now completely
erful quantitative framework for defining geologic history and for
absent.
identifying the rates and causes of geologic phenomena. Here we report
The distinctive erosional profile of the Sheepbed-Gillespie Lake conresults of an attempt to apply in-situ isotopic dating methods to Mars,
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In Situ Radiometric and Exposure Age
Dating of the Martian Surface

2. tact can be traced around the full width of Yellowknife Bay (9) with the
Sheepbed unit making up the floor of the encircled trough. This trough is
elongated in the NE-SW direction, creating an amphitheater-shaped
planimetric form open to the NE. Beyond the Gillespie Lake contact, the
more resistant units higher in the section form similar scarps stepping
upward a total of ~5 m to the uppermost unit of the Yellowknife Bay
formation (Fig. S1). Within the Sheepbed unit, mm- to cm-scale topographic protrusions form fields of small ridges that have been streamlined in the NE-SW direction (Fig. 2). Along with the morphology of the
Yellowknife Bay trough, this observations indicates a dominant role for
SW-directed wind erosion. These observations implicate eolian processes in eroding the mudstone, in efficiently wearing down any blocks that
are delivered to its surface from the encircling scarps or from distal impacts, and in expanding the exposure of the Yellowknife Bay formation.
Scientific investigations at Yellowknife Bay focused on the Sheepbed mudstone. This fine-grained (<50 μm) rock was drilled twice for
mineralogical and evolved gas analyses (11, 12). In addition, multiple
chemical analyses were obtained on outcropping mudstone as well as the
drill tailings. The two drilled samples, referred to as John Klein and
Cumberland, were located ~3 m apart, and yielded very similar results.
The mudstone is composed of detrital and authigenic components consisting of both crystalline and x-ray amorphous phases (11). The detrital
fraction includes minerals typical of volcanic rocks: plagioclase, pyroxenes, and minor olivine, sanidine and ilmenite. Crystalline authigenic
phases include smectitic clay (possibly saponite) and magnetite, thought
to have formed as a result of chemical alteration of detrital olivine, and
minor akaganeite, pyrrhotite, bassanite, and hematite. Quartz and halite
were reported, but very near the CheMin detection limit. Chlorate or
perchlorate was also tentatively identified (12). A model for the amorphous component, comprising about one third of the sample, indicates it
is composed mainly of Si, Fe, Ca, S, and Cl (11). It likely includes poorly crystalline or finely crystalline materials and may include detrital
volcanic and impact-derived glass. The presence of smectite, magnetite,
and akaganeite suggests that the mudstone has not experienced burial
heating above ~200°C, (11, 13). It is possible that the sample experienced no burial heating at all.
Geochronology Overview: K/Ar and Cosmogenic Isotopes
Noble gas isotopes can quantitatively constrain the age and erosion
history of the Sheepbed mudstone. 40Ar from 40K decay will record a
potassium-weighted average of the formation or cooling ages of the
multiple components of the mudstone. 36Ar, 21Ne, and 3He are produced
by irradiation of the uppermost ~2-3 m of the Martian surface by galactic
cosmic rays (GCRs) (14). These cosmogenic isotopes are commonly
used to assess exposure histories of meteorites (e.g., 15, 16) and erosion
rates and styles of terrestrial rocks (e.g., 17). Because the Martian atmosphere is very thin and the magnetic field very weak (18), the Martian
surface is only weakly shielded from GCRs. Thus cosmogenic isotope
production rates are much higher than on Earth (14, 19). The chemistry
of the Sheepbed mudstone (10) is such that the most abundant cosmogenic isotope is likely to be 36Ar produced from the capture of cosmogenic thermal neutrons by Cl, followed by 3He produced by spallation
mainly of O, Si, and Mg, followed by 21Ne from spallation of Mg, Si,
and Al (20). The mudstone’s exposure history is thus recorded by multiple isotopic systems.
The depth-dependence of the production functions of the two spallation isotopes are very similar: a small maximum at ~15 cm below the
surface reflecting development of the nuclear cascade in the uppermost
layers of rock, followed by an exponential decay with an e-folding depth
of ~1 m as the energetic particles attenuate (Fig. 3). In contrast, the production rate of 36Ar from neutron capture has a larger subsurface maximum at greater depth (~60 cm) arising from the combined effects of the
production of neutrons within the descending cascade and the loss of low
energy neutrons into the Martian atmosphere (e.g., 19).
The concentration of a single cosmogenic isotope yields a nonunique exposure history for the rock. The customary end-member interpretive models are to assume either no erosion, in which case a surface
exposure age is obtained, or steady erosion from great depth, in which
case a mean erosion rate is obtained (e.g., 17). Figure 3 shows that this
non-uniqueness can be eliminated by combining spallogenic and neutron
capture isotope measurements. In particular, a rock of Sheepbed composition initially at a depth of greater than a few meters that was instantaneously exposed at the surface would have 36Ar/3He of ~1.5 and
36
Ar/21Ne of ~13. In contrast, if steady erosion causes progressive
downward migration of the surface toward the sample, then the sample
integrates the entire depth profile including the large subsurface 36Ar
peak. Such a rock would have 36Ar/3He~4 and 36Ar/21Ne~30. In both
erosion scenarios the 3He/21Ne ratio is ~8; this isotope pair provides a
cross-check but no additional information on exposure history.
Results and Discussion
Geochronology measurements were performed on the Cumberland
drilled powder (21). After drilling, the sample was sieved and an aliquot
with estimated mass of 135 ± 18 mg (22) was introduced into a quartz
cup in the Sample Analysis at Mars (SAM) instrument. The cup was
moved into position in an oven, sealed against Mars atmosphere, and
evacuated. The sample was then heated to a maximum temperature of
~890°C for 25 min, and the evolved gases were purified and admitted
into the quadrupole mass spectrometer for analysis. All reported measurements used the high sensitivity semi-static analysis mode.
K-Ar Age
The Ar concentration and the APXS-determined K2O concentration
yield a K-Ar age of 4.21 ± 0.35 Ga (1σ) for the Cumberland sample
(Table 1). This age calculation assumes all measured 40Ar is radiogenic
(23). Although a fairly uniform level of excess Ar is thought to be present in some young Martian meteorites (24), that same level of excess
would contribute <0.03 Ga to the age of this high K2O, high Ar concentration rock. One important implication of this very high K-Ar age is that
processing in the SAM oven has extracted essentially all radiogenic 40Ar
despite a fairly low extraction temperature. This surprisingly high yield
(25) may result from rapid diffusive loss from the inherently fine grain
size of the mudstone (probably enhanced by the powdering process of
the drill (26)). Alternatively, the volatile constituents in the mudstone
may promote loss via flux-induced melting. Since fine grain size and
flux-melting will affect the noble gas isotopes similarly, effective extraction of 36Ar, 21Ne and 3He might also be expected. The high age also
implies that a very large fraction of the radiogenic Ar was retained in the
mudstone over geologic time.
The interpretation of the K-Ar age depends critically on where potassium is located in the rock. If a fraction FD of the potassium is in the
detrital phases and the remainder in authigenic phases, then the bulk age
(TB) is a potassium-weighted average of the age of the detritus (TD) and
the age of authigenesis (TA): TB=(1-FD)TA+FDTD. If all of the potassium
is carried in the detrital components (mainly sanidine, plagioclase and
possibly basalt glass), FD=1. In this case the K-Ar system records a mixture of the ages of components present in the crater rim, principally bedrock ranging from minimally to completely reset by the Gale-forming
impact. Crater rim lithologies as well as the crater itself are thought to
range from Noachian to early-Hesperian in age, or about 4.1 to 3.5 Ga
(5, 6, 27–29), in agreement with the K-Ar age of 4.21 ± 0.35 Ga we
measured. Because formation of K-bearing authigenic phases can only
lower the mudstone age below that of the detrital component, we conclude with 95% confidence (30) that the potassium-weighted mean age
of the materials in the Gale crater wall exceeds 3.6 Ga. Alternatively, if
the potassium is entirely hosted within authigenic components (phyllo-
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3. silicates or amorphous phases other than basalt glass), FD=0 and the age
records the formation age of those phases. In this case 4.21 Ga would
represent a minimum age of mudstone deposition.
At present we have no definitive way to determine the potassium
distribution in the mudstone, but we can make a reasonable estimate. Kbearing phases determined by CheMin include sanidine (1.8%), andesine
feldspar (21%) and an unknown fraction of basaltic or impact glass (11).
CheMin cannot determine the K2O content of any of these phases, so we
assume representative values of 13%, 0.3%, and 1%, respectively (31).
By assuming the mudstone contains 10% glass, we conclude that the
detrital component accounts for 80% of the measured K2O. The remainder could then be in the authigenic clay (18% of the mudstone) with
0.6% K2O, in agreement with K2O concentrations in saponite in a Martian meteorite (32). If we assume TD<4.1 Ga based on crater-count ages
of the Gale impact and host terrains, and use the 95% confidence lower
limit on the K-Ar age of 3.6 Ga, we obtain a current best estimate that
the mudstone was deposited prior to 1.6 Ga. Assuming either a younger
age for the detrital component or a smaller fraction of it in the mudstone
would cause this estimate to rise.
Cosmogenic 36Ar, 21Ne, and 3He
36
Ar, 21Ne, and 3He were all detected at levels that cannot be attributed to sources other than cosmic ray irradiation (33). In the mudstone, 36Ar/3He and 36Ar/21Ne are 1.7 ± 0.5 and 12 ± 5, respectively (34).
These ratios are within error of predictions of the no-erosion scenario
(1.5 and 13) and very different from the prediction of the steady erosion
scenario (4 and 30). Thus we cast our results in terms of surface exposure age, which for 3He, 21Ne, and 36Ar are 72 ± 15, 84 ± 28 and 79 ± 24
Ma, respectively. These ages could be the sum of multiple shorter exposure intervals separated by burial events, e.g., by exposure during initial
deposition and then again by recent re-exposure, or alternatively by burial and exhumation associated with migrating eolian deposits. However,
these events would have to involve rapid burial and removal of at least a
few meters of cover to maintain the good match of measured nuclide
concentration ratios to those of production at the surface.
The agreement among these results argues for complete extraction of
all three noble gases in the SAM oven, and against substantial loss of
noble gases over the ~78 Myr period of cosmic ray exposure. For example, diffusive loss of He from amorphous phases, plagioclase and phyllosilicates might occur at Mars ambient temperature (35), but the 3He/21Ne
ratio of ~7.5 ± 2.6 matches the expected production ratio of ~8. Similarly, dissolution and reprecipitation of a water-soluble Cl-rich phase by
occasional wetting of the mudstone might release accumulated 36Ar. If
this occurred to a significant extent, then the agreement between the 36Ar
exposure age and the 21Ne and 3He exposure ages would have to be fortuitous. While not impossible, we see no evidence for it in these data.
A significant portion of the 3He and 21Ne must be carried by detrital
minerals including plagioclase and pyroxene because these are important
host phases for the major target elements (36). In contrast, the enrichment of Cl compared to a typical Martian basalt suggests much of this
element was added to the mudstone from solution (9, 10). This distinction implies that, while 3He and 21Ne might record cosmic ray irradiation
that occurred during primary exposure and transport in addition to that
acquired during modern exposure at Yellowknife Bay, the same is not
true of 36Ar. The logical interpretation of the good agreement among all
three exposure ages is that all three reflect exposure only in the modern
setting.
The apparent absence of a detrital cosmogenic signal favors deposition of the mudstone in an environment in which erosion and transport
were fairly rapid and/or in which the Martian surface was shielded from
cosmic rays by a reasonably dense atmosphere. The transition from
comparatively wet conditions and a thick atmosphere to cold and dry
conditions with a thin atmosphere is thought to have occurred around the
Noachian-Hesperian boundary (37). Because wet conditions favor rapid
erosion, in either scenario the cosmogenic isotope observations would
support deposition of the Sheepbed mudstone shortly after Gale formation. Alternatively, deposition may have occurred in association with
a later event in which material was eroded and transported rapidly
enough to prevent detectable cosmogenic production. A late erosional
event has also been suggested for Amazonian-age fan formation in some
other Martian craters (38–40).
Topography, stratigraphy and surface exposure dating suggest that
the Yellowknife Bay trough is currently a focus of erosion, and that erosion is occurring by scarp retreat. The Sheepbed mudstone lies below a
sequence of relatively more resistant units that define a series of topographic steps (A-A’ in Fig. S1). The pace of wind erosion for the entire
escarpment will be set by the retreat rate of these more resistant units.
Deflation of the softer units, such as the mudstone, however, undercuts
and contributes to collapse of the resistant layers (Fig. 1), such that both
direct wind abrasion of resistant units and removal of the softer units
contribute to slope retreat. Resistant units and corresponding local steps
will thicken or thin as erosion sweeps into units with variable thicknesses and resistance properties. This predominately lateral erosion has
caused scarp migration to the southwestward and possibly other directions, and produced several meters of surface lowering. The general
flattening of the topographic profile (Fig. S1) as it extends into the Yellowknife Bay trough may indicate that a more resistant unit beneath the
Sheepbed mudstone has slowed continued removal of this unit.
In such a model, the scarp retreat rate can be estimated from the surface exposure ages. To prevent cosmogenic nuclide accumulation requires at least 2-3 m of overburden. Southwestward from the drill site
(and downwind, according to Fig. 3) this amount of overburden is first
encountered about 60 m away (Fig. S1). Thus, in a model in which the
mudstone is rapidly exposed from >2-3 m depth to the surface, the scarp
retreat rate over the last ~80 Ma averages ~0.75 m/Ma. At this rate, the
full extent of the Yellowknife Bay exposure could have been produced
over several hundred million years of steady lateral erosion. Alternatively, wind erosion and associated scarp retreat may be highly episodic,
perhaps in response to climatic variations tied to Mars’ obliquity cycle
(41, 42). Either way, surface exposure ages may vary substantially
around the Yellowknife Bay outcrop and other similar exposures, in
principle offering a test of the scarp retreat hypothesis.
Implications for Organic Preservation
Cosmic rays penetrating the uppermost several meters of rock create
a cascade of atomic and subatomic particles, electrons, and photons that
ionize molecules and atoms in their path (e.g., 43, 44). Complex organic
molecules are particularly susceptible to degradation by such particles,
and because these particles also produce the cosmogenic nuclides, we
have a way to assess the likely magnitude of this degradation in the
Cumberland sample. Degradation of organic molecules in Martian surface rocks subjected to cosmic ray irradiation has been modeled (44).
When scaled to the long-term cosmic ray dose implied by the cosmogenic nuclides in the Cumberland sample, these rates predict reductions of
between 2 and 3 orders of magnitude in the concentration of organic
molecules in the 100-400 AMU range.
The scarp retreat hypothesis offers a possible strategy for minimizing the degree of organic degradation in samples obtained during the
further course of exploration by Curiosity and possible future missions.
Because exposure ages and thus cosmic ray doses should decrease toward a bounding scarp (at least in the downwind direction), such a location may offer the best potential for organic preservation. Given our
estimated scarp retreat rate, locations within a few tens of cm of a fewmeter-scale scarp may have been exposed to cosmic rays for less than a
few Ma. Such a short exposure compares favorably to what can reasonably be expected from alternative sampling strategies relying on recent
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 3 / 10.1126/science.1247166

4. impact craters or drilling to obtain fresh strata.
References and Notes
1. M. H. Carr, J. W. Head III, Geologic History of Mars. Earth Planet. Sci. Lett.
294, 185–203 (2010). doi:10.1016/j.epsl.2009.06.042
2. E. M. Shoemaker, R. J. Hackman, R. E. Eggleton, “Interplanetary correlation
of geologic time,” in Advances in the Astronautical Sciences (Plenum, New
York, 1962), vol. 8, pp. 70–89.
3. W. K. Hartmann, G. Neukum, Cratering chronology and the evolution of Mars.
Space Sci. Rev. 96, 165–194 (2001). doi:10.1023/A:1011945222010
4. W. K. Hartmann, Martian cratering 8: Isochron refinement and the chronology
of Mars. Icarus 174, 294–320 (2005). doi:10.1016/j.icarus.2004.11.023
5. L. Le Deit, E. Hauber, F. Fueten, M. Pondrelli, A. P. Rossi, R. Jaumann,
Sequence of infilling events in Gale crater, Mars: Results from morphology,
stratigraphy, and mineralogy. J. Geophys. Res. Planets n/a (2013).
doi:10.1002/2012JE004322
6. B. J. Thomson, N. T. Bridges, R. Milliken, A. Baldridge, S. J. Hook, J. K.
Crowley, G. M. Marion, C. R. de Souza Filho, A. J. Brown, C. M. Weitz,
Constraints on the origin and evolution of the layered mound in Gale Crater,
Mars using Mars Reconnaissance Orbiter data. Icarus 214, 413–432 (2011).
doi:10.1016/j.icarus.2011.05.002
7. B. A. Ivanov, Mars/Moon cratering rate ratio estimates. Space Sci. Rev. 96, 87–
104 (2001). doi:10.1023/A:1011941121102
8. R. M. E. Williams, J. P. Grotzinger, W. E. Dietrich, S. Gupta, D. Y. Sumner, R.
C. Wiens, N. Mangold, M. C. Malin, K. S. Edgett, S. Maurice, O. Forni, O.
Gasnault, A. Ollila, H. E. Newsom, G. Dromart, M. C. Palucis, R. A. Yingst,
R. B. Anderson, K. E. Herkenhoff, S. Le Mouélic, W. Goetz, M. B. Madsen,
A. Koefoed, J. K. Jensen, J. C. Bridges, S. P. Schwenzer, K. W. Lewis, K. M.
Stack, D. Rubin, L. C. Kah, J. F. Bell, 3rd, J. D. Farmer, R. Sullivan, T. Van
Beek, D. L. Blaney, O. Pariser, R. G. Deen, O. Kemppinen, N. Bridges, J. R.
Johnson, M. Minitti, D. Cremers, L. Edgar, A. Godber, M. Wadhwa, D.
Wellington, I. McEwan, C. Newman, M. Richardson, A. Charpentier, L.
Peret, P. King, J. Blank, G. Weigle, M. Schmidt, S. Li, R. Milliken, K.
Robertson, V. Sun, M. Baker, C. Edwards, B. Ehlmann, K. Farley, J. Griffes,
H. Miller, M. Newcombe, C. Pilorget, M. Rice, K. Siebach, E. Stolper, C.
Brunet, V. Hipkin, R. Leveille, G. Marchand, P. Sobron Sanchez, L. Favot, G.
Cody, A. Steele, L. Fluckiger, D. Lees, A. Nefian, M. Martin, M. Gailhanou,
F. Westall, G. Israel, C. Agard, J. Baroukh, C. Donny, A. Gaboriaud, P.
Guillemot, V. Lafaille, E. Lorigny, A. Paillet, R. Perez, M. Saccoccio, C.
Yana, C. A. Aparicio, J. Caride Rodriguez, I. Carrasco Blazquez, F. Gomez
Gomez, J. G. Elvira, S. Hettrich, A. Lepinette Malvitte, M. Marin Jimenez, J.
M. Frias, J. M. Soler, F. J. M. Torres, A. Molina Jurado, L. M. Sotomayor, G.
Munoz Caro, S. Navarro Lopez, V. P. Gonzalez, J. P. Garcia, J. A. Rodriguez
Manfredi, J. J. R. Planello, S. Alejandra Sans Fuentes, E. Sebastian Martinez,
J. Torres Redondo, R. U. O’Callaghan, M.-P. Zorzano Mier, S. Chipera, J.-L.
Lacour, P. Mauchien, J.-B. Sirven, H. Manning, A. Fairen, A. Hayes, J.
Joseph, S. Squyres, P. Thomas, A. Dupont, A. Lundberg, N. Melikechi, A.
Mezzacappa, J. DeMarines, D. Grinspoon, G. Reitz, B. Prats, E. Atlaskin, M.
Genzer, A.-M. Harri, H. Haukka, H. Kahanpaa, J. Kauhanen, M. Paton, J.
Polkko, W. Schmidt, T. Siili, C. Fabre, J. Wray, M. B. Wilhelm, F.
Poitrasson, K. Patel, S. Gorevan, S. Indyk, G. Paulsen, D. Bish, J. Schieber,
B. Gondet, Y. Langevin, C. Geffroy, D. Baratoux, G. Berger, A. Cros, C.
Uston, J. Lasue, Q.-M. Lee, P.-Y. Meslin, E. Pallier, Y. Parot, P. Pinet, S.
Schroder, M. Toplis, E. Lewin, W. Brunner, E. Heydari, C. Achilles, D.
Oehler, B. Sutter, M. Cabane, D. Coscia, C. Szopa, F. Robert, V. Sautter, M.
Nachon, A. Buch, F. Stalport, P. Coll, P. Francois, F. Raulin, S. Teinturier, J.
Cameron, S. Clegg, A. Cousin, D. DeLapp, R. Dingler, R. S. Jackson, S.
Johnstone, N. Lanza, C. Little, T. Nelson, R. B. Williams, A. Jones, L.
Kirkland, A. Treiman, B. Baker, B. Cantor, M. Caplinger, S. Davis, B.
Duston, D. Fay, C. Hardgrove, D. Harker, P. Herrera, E. Jensen, M. R.
Kennedy, G. Krezoski, D. Krysak, L. Lipkaman, E. McCartney, S. McNair, B.
Nixon, L. Posiolova, M. Ravine, A. Salamon, L. Saper, K. Stoiber, K.
Supulver, J. Van Beek, R. Zimdar, K. L. French, K. Iagnemma, K. Miller, R.
Summons, F. Goesmann, S. Hviid, M. Johnson, M. Lefavor, E. Lyness, E.
Breves, M. D. Dyar, C. Fassett, D. F. Blake, T. Bristow, D. DesMarais, L.
Edwards, R. Haberle, T. Hoehler, J. Hollingsworth, M. Kahre, L. Keely, C.
McKay, L. Bleacher, W. Brinckerhoff, D. Choi, P. Conrad, J. P. Dworkin, J.
Eigenbrode, M. Floyd, C. Freissinet, J. Garvin, D. Glavin, D. Harpold, P.
Mahaffy, D. K. Martin, A. McAdam, A. Pavlov, E. Raaen, M. D. Smith, J.
Stern, F. Tan, M. Trainer, M. Meyer, A. Posner, M. Voytek, R. C. Anderson,
A. Aubrey, L. W. Beegle, A. Behar, D. Brinza, F. Calef, L. Christensen, J. A.
Crisp, L. DeFlores, J. Feldman, S. Feldman, G. Flesch, J. Hurowitz, I. Jun, D.
Keymeulen, J. Maki, M. Mischna, J. M. Morookian, T. Parker, B. Pavri, M.
Schoppers, A. Sengstacken, J. J. Simmonds, N. Spanovich, M. de la Torre
Juarez, A. R. Vasavada, C. R. Webster, A. Yen, P. D. Archer, F. Cucinotta, J.
H. Jones, D. Ming, R. V. Morris, P. Niles, E. Rampe, T. Nolan, M. Fisk, L.
Radziemski, B. Barraclough, S. Bender, D. Berman, E. N. Dobrea, R. Tokar,
D. Vaniman, L. Leshin, T. Cleghorn, W. Huntress, G. Manhes, J. Hudgins, T.
Olson, N. Stewart, P. Sarrazin, J. Grant, E. Vicenzi, S. A. Wilson, M. Bullock,
B. Ehresmann, V. Hamilton, D. Hassler, J. Peterson, S. Rafkin, C. Zeitlin, F.
Fedosov, D. Golovin, N. Karpushkina, A. Kozyrev, M. Litvak, A. Malakhov,
I. Mitrofanov, M. Mokrousov, S. Nikiforov, V. Prokhorov, A. Sanin, V.
Tretyakov, A. Varenikov, A. Vostrukhin, R. Kuzmin, B. Clark, M. Wolff, S.
McLennan, O. Botta, D. Drake, K. Bean, M. Lemmon, E. M. Lee, R.
Sucharski, M. A. P. Hernandez, J. J. Blanco Avalos, M. Ramos, M.-H. Kim,
C. Malespin, I. Plante, J.-P. Muller, R. N. Gonzalez, R. Ewing, W. Boynton,
R. Downs, M. Fitzgibbon, K. Harshman, S. Morrison, O. Kortmann, A.
Williams, G. Lugmair, M. A. Wilson, B. Jakosky, T. B. Zunic, J. Frydenvang,
K. Kinch, S. L. S. Stipp, N. Boyd, J. L. Campbell, R. Gellert, G. Perrett, I.
Pradler, S. VanBommel, S. Jacob, T. Owen, S. Rowland, H. Savijarvi, E.
Boehm, S. Bottcher, S. Burmeister, J. Guo, J. Kohler, C. M. Garcia, R. M.
Mellin, R. W. Schweingruber, T. McConnochie, M. Benna, H. Franz, H.
Bower, A. Brunner, H. Blau, T. Boucher, M. Carmosino, S. Atreya, H. Elliott,
D. Halleaux, N. Renno, M. Wong, R. Pepin, B. Elliott, J. Spray, L.
Thompson, S. Gordon, J. Williams, P. Vasconcelos, J. Bentz, K. Nealson, R.
Popa, J. Moersch, C. Tate, M. Day, G. Kocurek, B. Hallet, R. Sletten, R.
Francis, E. McCullough, E. Cloutis, I. L. ten Kate, R. Arvidson, A. Fraeman,
D. Scholes, S. Slavney, T. Stein, J. Ward, J. Berger, J. E. Moores, MSL
Science Team, Martian fluvial conglomerates at Gale crater. Science 340,
1068–1072 (2013). doi:10.1126/science.1237317 Medline
9. J. P. Grotzinger et al., A habitable fluvio-lacustrine environment at
Yellowknife Bay, Gale Crater, Mars. Science, published online 9 December
2013 (10.1126/science.1242777).
10. S. M. McLennan et al., Elemental geochemistry of sedimentary rocks in
Yellowknife Bay, Gale Crater, Mars. Science, published online 9 December
2013 (10.1126/science.1244734).
11. D. Vaniman et al., Mineralogy of a mudstone on Mars. Science, published
online 9 December 2013 (10.1126/science.1243480).
12. D. W. Ming et al., Organic, volatile, and isotopic compositions of a
sedimentary rock in Yellowknife Bay, Gale Crater, Mars. Science, published
online 9 December 2013 (10.1126/science.1245267).
13. L. P. Keller, K. L. Thomas, R. N. Clayton, T. K. Mayeda, J. M. DeHart, D. S.
McKay, Aqueous alteration of the Bali CV3 chondrite: evidence from
mineralogy, mineral chemistry, and oxygen isotopic compositions. Geochim.
Cosmochim. Acta 58, 5589–5598 (1994). doi:10.1016/0016-7037(94)90252-6
Medline
14. D. Lal, Cosmogenic and nucleogenic isotopic changes in Mars: their rates and
implications to the evolutionary history of Martian surface. Geochim.
Cosmochim. Acta 57, 4627–4637 (1993). doi:10.1016/0016-7037(93)90188-3
Medline
15. O. Eugster, Cosmic-ray exposure ages of meteorites and lunar rocks and their
significance. Chemie Der Erde-Geochemistry 63, 3–30 (2003).
doi:10.1078/0009-2819-00021
16. K. Marti, T. Graf, Cosmic-ray exposure history of ordinary chondrites. Annu.
Rev.
Earth
Planet.
Sci.
20,
221–243
(1992).
doi:10.1146/annurev.ea.20.050192.001253
17. T. Cerling, H. Craig, Geomorphology and in-situ cosmogenic isotopes. Annu.
Rev.
Earth
Planet.
Sci.
22,
273–317
(1994).
doi:10.1146/annurev.ea.22.050194.001421
18. M. H. Acuña, J. E. P. Connerney, P. Wasilewski, R. P. Lin, K. A. Anderson,
C. W. Carlson, J. McFadden, D. W. Curtis, D. Mitchell, H. Reme, C. Mazelle,
J. A. Sauvaud, C. d’Uston, A. Cros, J. L. Medale, S. J. Bauer, P. Cloutier, M.
Mayhew, D. Winterhalter, N. F. Ness, Magnetic field and plasma observations
at Mars: Initial results of the Mars global surveyor mission. Science 279,
1676–1680 (1998). doi:10.1126/science.279.5357.1676 Medline
19. M. N. Rao, D. D. Bogard, L. E. Nyquist, D. S. McKay, J. Masarik, Neutron
capture isotopes in the martian regolith and implications for Martian
atmospheric
noble
gases.
Icarus
156,
352–372
(2002).
doi:10.1006/icar.2001.6809
20. Cosmogenic production rate calculations are given in the supplementary
materials.
21. Full method details are provided in the supplementary materials.
22. Details of mass estimate and uncertainty are given in the supplementary
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 4 / 10.1126/science.1247166

5. materials.
23. Atmospheric and excess argon are assumed negligible, as described in the
supplementary materials.
24. D. Bogard, J. Park, D. Garrison, 39Ar-40Ar “ages” and origin of excess 40Ar
in Martian shergottites. Meteorit. Planet. Sci. 44, 905–923 (2009).
doi:10.1111/j.1945-5100.2009.tb00777.x
25. Full release of Ar for Ar geochronology often requires much higher
temperatures. See supplementary materials for a discussion of this issue.
26. R. C. Anderson, L. Jandura, A. B. Okon, D. Sunshine, C. Roumeliotis, L. W.
Beegle, J. Hurowitz, B. Kennedy, D. Limonadi, S. McCloskey, M. Robinson,
C. Seybold, K. Brown, Collecting samples in Gale Crater, Mars; an overview
of the Mars Science Laboratory sample acquisition, sample processing and
handling system. Space Sci. Rev. 170, 57–75 (2012). doi:10.1007/s11214-0129898-9
27. D. H. Scott, M. G. Chapman, Geologic and topographic maps of the Elysium
paleolake basin, Mars. U.S. Geol. Surv. Misc. Invest. Map, I-2397 (1995).
28. R. Greeley, J. E. Guest, Geologic map of the eastern equatorial region of
Mars. U.S. Geol. Surv. Misc. Invest. Map I-1802-B (1987).
29. J. J. Wray, Gale crater: the Mars Science Laboratory/Curiosity rover landing
site. Int. J. Astrobiol. 12, 25–38 (2013). doi:10.1017/S1473550412000328
30. Using the cumlative normal distribution.
31. Potassium concentrations were estimated from terrestrial examples of
volcanic sanidine and andesine [e.g., (45, 46)]. The relatively high K2O
content assumed for the basalt glass is consistent with ongoing analyses of
basalts in Gale crater. The K2O concentration and glass abundance can be
traded off to yield the same overall mass balance.
32. J. C. Bridges, S. P. Schwenzer, The nakhlite hydrothermal brine on Mars.
Earth
Planet.
Sci.
Lett.
359-360,
117–123
(2012).
doi:10.1016/j.epsl.2012.09.044
33. Possible alternative sources and why they can be beglected are described in
the supplementary materials.
34. Mass errors cancel in these ratios.
35. Laboratory data bearing on the question of diffusive noble gas loss are given
in the supplementary materials.
36. Likely host minerals for each of the noble gases are given in the supplemntary
materials.
37. J.-P. Bibring, Y. Langevin, J. F. Mustard, F. Poulet, R. Arvidson, A. Gendrin,
B. Gondet, N. Mangold, P. Pinet, F. Forget, M. Berthé, J. P. Bibring, A.
Gendrin, C. Gomez, B. Gondet, D. Jouglet, F. Poulet, A. Soufflot, M.
Vincendon, M. Combes, P. Drossart, T. Encrenaz, T. Fouchet, R. Merchiorri,
G. Belluci, F. Altieri, V. Formisano, F. Capaccioni, P. Cerroni, A. Coradini,
S. Fonti, O. Korablev, V. Kottsov, N. Ignatiev, V. Moroz, D. Titov, L.
Zasova, D. Loiseau, N. Mangold, P. Pinet, S. Douté, B. Schmitt, C. Sotin, E.
Hauber, H. Hoffmann, R. Jaumann, U. Keller, R. Arvidson, J. F. Mustard, T.
Duxbury, F. Forget, G. Neukum, Global mineralogical and aqueous mars
history derived from OMEGA/Mars Express data. Science 312, 400–404
(2006). doi:10.1126/science.1122659 Medline
38. J. A. Grant, S. A. Wilson, Late alluvial fan formation in southern Margaritifer
Terra,
Mars.
Geophys.
Res.
Lett.
38,
L08201
(2011).
doi:10.1029/2011GL046844
39. J. A. Grant, S. A. Wilson, A possible synoptic source of water for alluvial fan
formation in southern Margaritifer Terra, Mars. Planet. Space Sci. 72, 44–52
(2012). doi:10.1016/j.pss.2012.05.020
40. N. Mangold, E. S. Kite, M. G. Kleinhans, H. Newsom, V. Ansan, E. Hauber,
E. Kraal, C. Quantin, K. Tanaka, The origin and timing of fluvial activity at
Eberswalde
crater,
Mars.
Icarus
220,
530–551
(2012).
doi:10.1016/j.icarus.2012.05.026
41. J. Laskar, A. C. M. Correia, M. Gastineau, F. Joutel, B. Levrard, P. Robutel,
Long term evolution and chaotic diffusion of the insolation quantities of Mars.
Icarus 170, 343–364 (2004). doi:10.1016/j.icarus.2004.04.005
42. W. R. Ward, Large-scale variations in the obliquity of Mars. Science 181,
260–262 (1973). doi:10.1126/science.181.4096.260 Medline
43. L. R. Dartnell, L. Desorgher, J. M. Ward, A. J. Coates, Modelling the surface
and subsurface Martian radiation environment: Implications for astrobiology.
Geophys. Res. Lett. 34, L02207 (2007). doi:10.1029/2006GL027494
44. A. A. Pavlov, G. Vasilyev, V. M. Ostryakov, A. K. Pavlov, P. Mahaffy,
Degradation of the organic molecules in the shallow subsurface of Mars due
to irradiation by cosmic rays. Geophys. Res. Lett. 39, L13202 (2012).
doi:10.1029/2012GL052166
45. W. A. Deer, R. A. Howie, J. Zussman, Rock-Forming Minerals, Volume 4A:
Framework Silicates - Feldspars. (Geological Society of London, London,
2001).
46. O. Bachmann, M. A. Dungan, P. W. Lipman, The Fish Canyon magma body,
San Juan volcanic field, Colorado: Rejuvenation and eruption of an uppercrustal
batholith.
J.
Petrol.
43,
1469–1503
(2002).
doi:10.1093/petrology/43.8.1469
47. Calculations provided in supplementary materials.
48. P. R. Mahaffy, C. R. Webster, M. Cabane, P. G. Conrad, P. Coll, S. K. Atreya,
R. Arvey, M. Barciniak, M. Benna, L. Bleacher, W. B. Brinckerhoff, J. L.
Eigenbrode, D. Carignan, M. Cascia, R. A. Chalmers, J. P. Dworkin, T.
Errigo, P. Everson, H. Franz, R. Farley, S. Feng, G. Frazier, C. Freissinet, D.
P. Glavin, D. N. Harpold, D. Hawk, V. Holmes, C. S. Johnson, A. Jones, P.
Jordan, J. Kellogg, J. Lewis, E. Lyness, C. A. Malespin, D. K. Martin, J.
Maurer, A. C. McAdam, D. McLennan, T. J. Nolan, M. Noriega, A. A.
Pavlov, B. Prats, E. Raaen, O. Sheinman, D. Sheppard, J. Smith, J. C. Stern,
F. Tan, M. Trainer, D. W. Ming, R. V. Morris, J. Jones, C. Gundersen, A.
Steele, J. Wray, O. Botta, L. A. Leshin, T. Owen, S. Battel, B. M. Jakosky, H.
Manning, S. Squyres, R. Navarro-González, C. P. McKay, F. Raulin, R.
Sternberg, A. Buch, P. Sorensen, R. Kline-Schoder, D. Coscia, C. Szopa, S.
Teinturier, C. Baffes, J. Feldman, G. Flesch, S. Forouhar, R. Garcia, D.
Keymeulen, S. Woodward, B. P. Block, K. Arnett, R. Miller, C. Edmonson, S.
Gorevan, E. Mumm, The Sample Analysis at Mars investigation and
instrument suite. Space Sci. Rev. 170, 401–478 (2012). doi:10.1007/s11214012-9879-z
49. National Geochronological Database, United States Geological Survey OpenFile Report 2003-23, http://geopubs.wr.usgs.gov/open-file/of03-236/ (2013).
50. P. R. Renne, G. Balco, K. R. Ludwig, R. Mundil, K. Min, Response to the
comment by W.H. Schwarz et al. on “Joint determination of 40K decay
constants and 40Ar*/40K for the Fish Canyon sanidine standard, and improved
accuracy for 40Ar/39Ar geochronology” by P.R. Renne et al. (2010). Geochim.
Cosmochim. Acta 75, 5097–5100 (2011). doi:10.1016/j.gca.2011.06.021
51. P. R. Mahaffy, C. R. Webster, S. K. Atreya, H. Franz, M. Wong, P. G.
Conrad, D. Harpold, J. J. Jones, L. A. Leshin, H. Manning, T. Owen, R. O.
Pepin, S. Squyres, M. Trainer, O. Kemppinen, N. Bridges, J. R. Johnson, M.
Minitti, D. Cremers, J. F. Bell, L. Edgar, J. Farmer, A. Godber, M. Wadhwa,
D. Wellington, I. McEwan, C. Newman, M. Richardson, A. Charpentier, L.
Peret, P. King, J. Blank, G. Weigle, M. Schmidt, S. Li, R. Milliken, K.
Robertson, V. Sun, M. Baker, C. Edwards, B. Ehlmann, K. Farley, J. Griffes,
J. Grotzinger, H. Miller, M. Newcombe, C. Pilorget, M. Rice, K. Siebach, K.
Stack, E. Stolper, C. Brunet, V. Hipkin, R. Leveille, G. Marchand, P. S.
Sanchez, L. Favot, G. Cody, A. Steele, L. Fluckiger, D. Lees, A. Nefian, M.
Martin, M. Gailhanou, F. Westall, G. Israel, C. Agard, J. Baroukh, C. Donny,
A. Gaboriaud, P. Guillemot, V. Lafaille, E. Lorigny, A. Paillet, R. Perez, M.
Saccoccio, C. Yana, C. Armiens-Aparicio, J. C. Rodriguez, I. C. Blazquez, F.
G. Gomez, J. Gomez-Elvira, S. Hettrich, A. L. Malvitte, M. M. Jimenez, J.
Martinez-Frias, J. Martin-Soler, F. J. Martin-Torres, A. M. Jurado, L. MoraSotomayor, G. M. Caro, S. N. Lopez, V. Peinado-Gonzalez, J. Pla-Garcia, J.
A. R. Manfredi, J. J. Romeral-Planello, S. A. S. Fuentes, E. S. Martinez, J. T.
Redondo, R. Urqui-O’Callaghan, M.-P. Z. Mier, S. Chipera, J.-L. Lacour, P.
Mauchien, J.-B. Sirven, A. Fairen, A. Hayes, J. Joseph, R. Sullivan, P.
Thomas, A. Dupont, A. Lundberg, N. Melikechi, A. Mezzacappa, J.
DeMarines, D. Grinspoon, G. Reitz, B. Prats, E. Atlaskin, M. Genzer, A.-M.
Harri, H. Haukka, H. Kahanpaa, J. Kauhanen, O. Kemppinen, M. Paton, J.
Polkko, W. Schmidt, T. Siili, C. Fabre, J. Wray, M. B. Wilhelm, F.
Poitrasson, K. Patel, S. Gorevan, S. Indyk, G. Paulsen, S. Gupta, D. Bish, J.
Schieber, B. Gondet, Y. Langevin, C. Geffroy, D. Baratoux, G. Berger, A.
Cros, C. d’Uston, O. Forni, O. Gasnault, J. Lasue, Q.-M. Lee, S. Maurice, P.Y. Meslin, E. Pallier, Y. Parot, P. Pinet, S. Schroder, M. Toplis, E. Lewin, W.
Brunner, E. Heydari, C. Achilles, D. Oehler, B. Sutter, M. Cabane, D. Coscia,
G. Israel, C. Szopa, G. Dromart, F. Robert, V. Sautter, S. Le Mouelic, N.
Mangold, M. Nachon, A. Buch, F. Stalport, P. Coll, P. Francois, F. Raulin, S.
Teinturier, J. Cameron, S. Clegg, A. Cousin, D. DeLapp, R. Dingler, R. S.
Jackson, S. Johnstone, N. Lanza, C. Little, T. Nelson, R. C. Wiens, R. B.
Williams, A. Jones, L. Kirkland, A. Treiman, B. Baker, B. Cantor, M.
Caplinger, S. Davis, B. Duston, K. Edgett, D. Fay, C. Hardgrove, D. Harker,
P. Herrera, E. Jensen, M. R. Kennedy, G. Krezoski, D. Krysak, L. Lipkaman,
M. Malin, E. McCartney, S. McNair, B. Nixon, L. Posiolova, M. Ravine, A.
Salamon, L. Saper, K. Stoiber, K. Supulver, J. Van Beek, T. Van Beek, R.
Zimdar, K. L. French, K. Iagnemma, K. Miller, R. Summons, F. Goesmann,
W. Goetz, S. Hviid, M. Johnson, M. Lefavor, E. Lyness, E. Breves, M. D.
Dyar, C. Fassett, D. F. Blake, T. Bristow, D. DesMarais, L. Edwards, R.
Haberle, T. Hoehler, J. Hollingsworth, M. Kahre, L. Keely, C. McKay, M. B.
Wilhelm, L. Bleacher, W. Brinckerhoff, D. Choi, J. P. Dworkin, J.
Eigenbrode, M. Floyd, C. Freissinet, J. Garvin, D. Glavin, A. Jones, D. K.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 5 / 10.1126/science.1247166

6. Martin, A. McAdam, A. Pavlov, E. Raaen, M. D. Smith, J. Stern, F. Tan, M.
Meyer, A. Posner, M. Voytek, R. C. Anderson, A. Aubrey, L. W. Beegle, A.
Behar, D. Blaney, D. Brinza, F. Calef, L. Christensen, J. A. Crisp, L.
DeFlores, B. Ehlmann, J. Feldman, S. Feldman, G. Flesch, J. Hurowitz, I. Jun,
D. Keymeulen, J. Maki, M. Mischna, J. M. Morookian, T. Parker, B. Pavri,
M. Schoppers, A. Sengstacken, J. J. Simmonds, N. Spanovich, M. T. Juarez,
A. R. Vasavada, A. Yen, P. D. Archer, F. Cucinotta, D. Ming, R. V. Morris,
P. Niles, E. Rampe, T. Nolan, M. Fisk, L. Radziemski, B. Barraclough, S.
Bender, D. Berman, E. N. Dobrea, R. Tokar, D. Vaniman, R. M. E. Williams,
A. Yingst, K. Lewis, T. Cleghorn, W. Huntress, G. Manhes, J. Hudgins, T.
Olson, N. Stewart, P. Sarrazin, J. Grant, E. Vicenzi, S. A. Wilson, M. Bullock,
B. Ehresmann, V. Hamilton, D. Hassler, J. Peterson, S. Rafkin, C. Zeitlin, F.
Fedosov, D. Golovin, N. Karpushkina, A. Kozyrev, M. Litvak, A. Malakhov,
I. Mitrofanov, M. Mokrousov, S. Nikiforov, V. Prokhorov, A. Sanin, V.
Tretyakov, A. Varenikov, A. Vostrukhin, R. Kuzmin, B. Clark, M. Wolff, S.
McLennan, O. Botta, D. Drake, K. Bean, M. Lemmon, S. P. Schwenzer, R. B.
Anderson, K. Herkenhoff, E. M. Lee, R. Sucharski, M. A. P. Hernandez, J. J.
B. Avalos, M. Ramos, M.-H. Kim, C. Malespin, I. Plante, J.-P. Muller, R.
Navarro-Gonzalez, R. Ewing, W. Boynton, R. Downs, M. Fitzgibbon, K.
Harshman, S. Morrison, W. Dietrich, O. Kortmann, M. Palucis, D. Y.
Sumner, A. Williams, G. Lugmair, M. A. Wilson, D. Rubin, B. Jakosky, T.
Balic-Zunic, J. Frydenvang, J. K. Jensen, K. Kinch, A. Koefoed, M. B.
Madsen, S. L. S. Stipp, N. Boyd, J. L. Campbell, R. Gellert, G. Perrett, I.
Pradler, S. VanBommel, S. Jacob, S. Rowland, E. Atlaskin, H. Savijarvi, E.
Boehm, S. Bottcher, S. Burmeister, J. Guo, J. Kohler, C. M. Garcia, R.
Mueller-Mellin, R. Wimmer-Schweingruber, J. C. Bridges, T. McConnochie,
M. Benna, H. Bower, A. Brunner, H. Blau, T. Boucher, M. Carmosino, H.
Elliott, D. Halleaux, N. Renno, B. Elliott, J. Spray, L. Thompson, S. Gordon,
H. Newsom, A. Ollila, J. Williams, P. Vasconcelos, J. Bentz, K. Nealson, R.
Popa, L. C. Kah, J. Moersch, C. Tate, M. Day, G. Kocurek, B. Hallet, R.
Sletten, R. Francis, E. McCullough, E. Cloutis, I. L. ten Kate, R. Kuzmin, R.
Arvidson, A. Fraeman, D. Scholes, S. Slavney, T. Stein, J. Ward, J. Berger, J.
E. Moores; MSL Science Team, Abundance and isotopic composition of
gases in the martian atmosphere from the Curiosity rover. Science 341, 263–
266 (2013). doi:10.1126/science.1237966 Medline
52. V. A. Krasnopolsky, G. R. Gladstone, Helium on Mars and Venus: EUVE
observations
and
modeling.
Icarus
176,
395–407
(2005).
doi:10.1016/j.icarus.2005.02.005
53. K. A. Farley, J. Libarkin, S. Mukhopadhyay, W. Amidon, Cosmogenic and
nucleogenic He-3 in apatite, titanite, and zircon. Earth Planet. Sci. Lett. 248,
451–461 (2006). doi:10.1016/j.epsl.2006.06.008
54. K. A. Farley, Cenozoic variations in the flux of interplanetary dust recorded
by 3He in a deep sea sediment. Nature 376, 153–156 (1995).
doi:10.1038/376153a0
55. D. D. Bogard, K-Ar dating of rocks on Mars: Requirements from Martian
meteorite analyses and isochron modeling. Meteorit. Planet. Sci. 44, 3–14
(2009). doi:10.1111/j.1945-5100.2009.tb00713.x
56. W. S. Cassata, P. R. Renne, Systematic variations of argon diffusion in
feldspars and implications for thermochronometry. Geochim. Cosmochim.
Acta 112, 251–287 (2013). doi:10.1016/j.gca.2013.02.030
57. L. Gourbet, D. L. Shuster, G. Balco, W. S. Cassata, P. R. Renne, D. Rood,
Neon diffusion kinetics in olivine, pyroxene and feldspar:Retentivity of
cosmogenic and nucleogenic neon. Geochim. Cosmochim. Acta 86, 21–36
(2012). doi:10.1016/j.gca.2012.03.002
58. D. L. Shuster, K. A. Farley, Diffusion kinetics of proton-induced 21Ne, 3He,
and 4He in quartz. Geochim. Cosmochim. Acta 69, 2349–2359 (2005).
doi:10.1016/j.gca.2004.11.002
59. P. H. Blard, N. Puchol, K. A. Farley, Constraints on the loss of matrix-sited
helium during vacuum crushing of mafic phenocrysts. Geochim. Cosmochim.
Acta 72, 3788–3803 (2008). doi:10.1016/j.gca.2008.05.044
60. T. D. Swindle, D. A. Kring, M. K. Burkland, D. H. Hill, W. V. Boynton,
Noble gases, bulk chemistry, and petrography of olivine-rich achondrites
Eagles Nest and Lewis Cliff 88763: Comparison to brachinites. Meteorit.
Planet. Sci. 33, 31–48 (1998). doi:10.1111/j.1945-5100.1998.tb01605.x
61. D. D. Bogard, L. E. Nyquist, B. M. Bansal, H. Wiesmann, C. Y. Shih, 76535 Old Lunar Rock. Earth Planet. Sci. Lett. 26, 69–80 (1975). doi:10.1016/0012821X(75)90178-8
62. J. N. Goswami, N. Sinha, S. V. S. Murty, R. K. Mohapatra, C. J. Clement,
Nuclear tracks and light noble gases in Allan Hills 84001: Preatmospheric
size, fail characteristics, cosmic-ray exposure duration and formation age.
Meteorit. Planet. Sci. 32, 91–96 (1997). doi:10.1111/j.19455100.1997.tb01244.x
63. T. Cerling, Dating geomorphic surfaces using cosmogenic 3He. Quat. Res. 33,
148–156 (1990). doi:10.1016/0033-5894(90)90015-D
64. A. Jambon, J. S. Shelby, Helium diffusion and solubility in obsidians and
basaltic glass in the range 200–300°C. Earth Planet. Sci. Lett. 51, 206–214
(1980). doi:10.1016/0012-821X(80)90268-X
65. R. Wieler, in Noble Gases in Geochemistry and Cosmochemistry, D. Porcelli,
C. J. Ballentine, R. Wieler, Eds. (2002), vol. 47, pp. 125–170.
66. S. R. Taylor, S. M. McLennan, Planetary Crusts: Their Composition, Origin,
and Evolution (Cambridge University Press, Cambridge, 2009), pp. 378.
67. G. J. Taylor, The bulk composition of Mars. Chemie Der Erde-Geochemistry,
published online 5 October 2013 (10.1016/j.chemer.2013.09.006).
Acknowledgments: The authors are indebted to the Mars Science Laboratory
Project engineering and management teams for their exceptionally skilled and
diligent efforts in making the mission as effective as possible and enhancing
science operations. We are also grateful to all those MSL team members who
participated in tactical and strategic operations. Without the support of both
the engineering and science teams, the data presented here could not have
been collected. Three anonymous reviewers provided many helpful
suggestions. Some of this research was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under a contract with the
National Aeronautics and Space Administration. Data presented in this paper
are archived in the Planetary Data System (pds.nasa.gov).
Supplementary Materials
www.sciencemag.org/cgi/content/1247166/DC1
Materials and Methods
Figs. S1 to S3
Tables S1 to S4
References (48–67)
14 October 2013; accepted 25 November 2013
Published online 09 December 2013
10.1126/science.1247166
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 6 / 10.1126/science.1247166

7. Table 1. Geochronology data.
Sheepbed Mudstone
Cumberland Sample
Sample Mass
K-Ar System
K2O (wt %)
40
Ar (nmol/g)
K-Ar Age (Ga)
0.135 ± 0.018 g
±1σ
0.50
0.08
11.95
1.71
4.21
0.35
Cosmogenic Isotopes
Isotope
3
He
21
Ne
36
Ar
pmol/g
33.7
4.49
55.6
±
6.9
1.52
16.8
PR (pmol g−1 Ma−1)A
Surface
2m Average
0.466
0.254
0.054
0.034
0.714
1.029
Exposure AgeB
(Ma)
±
72
15
84
28
78
24
Notes: elemental composition from APXS measurement of Cumberland drill tailings. AModel isotope production rate (47).
BSurface exposure age assuming no erosion.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 7 / 10.1126/science.1247166

8. Fig. 1. Mastcam view looking 79° west of North. With increasing distance the Yellowknife Bay formation includes the
Sheepbed mudstone, Gillespie Lake sandstone, and Point Lake outcrop (36 m away). In the distance, the mostly rockand sand-covered Bradbury rise is visible. The large outcrop on the near horizon (marked “x”) is 240 m distant and
stands 13 m above the Gillespie Lake-Sheepbed contact. This is a portion of a 40 frame M-100 mosaic taken on Sol
188 between 13:27 and 13:48 LMST (2013-02-14 23:41:35 and 2013-02-15 00:03:23 PST). The images in the full
mosaic, acquired as sequence mcam01009, have picture IDs between 0188MR0010090000202415I01 and
0188MR0010090390202454I01.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 8 / 10.1126/science.1247166

9. Fig. 2. Mars Hand Lens Imager (MAHLI) image of brushed,
gray bedrock outcrop of Sheepbed mudstone near the
Cumberland drill hole. Protrusion of nodules (9) results from
eolian scouring of rock surface, creating wind-tails. Preference
for steep faces of wind-tails on NE side suggests long-term
averaged paleowind direction from NE to SW. This is a portion
of MAHLI image 0291MH0001970010103390C00, acquired
on Sol 291. Illumination from the top/upper left.
Fig. 3. Depth dependence of cosmogenic isotope production rates
3
modeled for a rock of Cumberland mudstone chemistry on Mars. He
21
36
and Ne are spallation isotopes, while Ar is produced by capture of
3
21
cosmogenic neutrons. Note the multiplicative factors applied to He and Ne.
3
A mudstone bulk density of 2.6 g/cm was assumed to convert overburden
mass to linear depth.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 9 / 10.1126/science.1247166