There is abundant geomorphic evidence to suggest that Mars once had a much denser and warmer atmosphere than present today. Outflow channel, ancient valley networks, and degraded impact craters in the highlands all suggest that ancient Martian atmospheric conditions supported liquid water on the surface. The pressure, composition, and duration of this atmosphere is largely unknown. However, we have attempted to place some constraints on the nature of the early Martian atmosphere by analyzing morphologic variations of highland impact crater populations, synthesizing results of other investigators, and incorporating what is know about the geologic history of the early Earth. This is important for understanding the climatic evolution of Mars, the relative abundance of martian volatiles, and the nature of highland surface materials

Craddock, R. A.

Maxwell, T. A.

English

NASA Technical Reports Server

LPI Technicol Report 93-03, Parr 1 9
major volcanic centers such as Tharsis and Elysium). Note th at, with
the exception of active geothermal areas, the flow velocities associ-
ated with these processes are likely to be orders of magnitude
smaller than those that characterize precipitation-driven systems on
Earth.
References: [1] Masursky et al. (1977)JGR, 82,4016--4038.
[2] Pollack et al. (1987) Icarus, 71,203-224. [3] Clifford S. M.
(1991) GRL, 18, 2055--2058. [4] Clifford S. M., this volume.
[5] Mifflin M. D. and Hess J. W. (1979) J. Hydrol.. 43, 217-237.
[6] Cathles L. M. (1990) Science, 248, 323-329. [7] Fanale et al.
(1986) Icarus, 67, 1-18. [8 ] Cart M. H. (1979) JGR, 84.2995-3007.
[9] Soderblom L. A. and Weaner D. B. (1978) Icarus, 34, 622-637,
[10] Newsom H. E. (1980) Icarus, 44, 207-216. [11] Brakem'idge
et al. (1985) Geology, 13, 859-862. [12] Gulick V. C. (1991)
Workshop on the Martian Surface and Atmosphere Through Time,
50-51. [ 13] Pieri D. (1980) Scie2we, 210 8957897. [14] Cart M. H'
(1983) lcarus. 56,476--4_ 9 4 i 2 1 6 6 7
t f_T HE_A_ _M/A RTI_A N_E_VIR_O_NN M_/_'ENT( C_L U'TES_-F_ L
THE CRATERED HIGHLANDS AND THE PRECAMB RIAN
EARTH. R.A. Craddock and T. A. Maxwell, Center for Earth
and Planetary Studies, National Air and Space Mu scum, Smithsonian
Institution, Washington DC 20560, USA.
There is abundant geomorphic evidence to suggest that Mars
once had a much denser and warmer atmosphere than present today.
Outflow channels [1], ancient valley networks [2]_ and degraded
impact craters in the highlands [3] all suggest that ancient martian
atmospheric conditions supported liquid water on the surface. The
pressure, composition, and duration of this atmosphere is largely
unknown. However, we have attempted to place some constraints on
the nature ofthe early martian atmosphere by analyzing morphologic
variations of highland impact crater populations, synthesizing re-
sults of other investigators, and incorporating what is known about
the geologic history of the early Earth. This is important for
understanding the climatic evolution of Mars, the relative abun-
dance of martian volatiles, and the nature of highland surface
materials.
The duration of the martian primordial atmosphere and the
interval of time water existed as a liquid on the surface can be
estimated from the ages of features thou ght to have formed by fluvial
processes. Formation of the large outflow channels occurred from
the late Noachian (e.g.. Ma'adim Vallis [4]) until the early Amazo-
nian (e.g., Mangala Valles [5]). Fomaation of the ancient valley
networks [6] and degradation of the cratered highlands [3] also
occurred during this period, and the timing of both these processes
appears to be dependent upon elevation. Fomlation of valley
networks and degradation of highland impact craters ceased at
higher elevations before they shut off at lower elevations. This
implies that the highland volatile reservoir became depleted with
time or, alternatively, the density of the martian atmosphere de-
creased with time. In the latter scenario, precipitation would occur
throughout the highlands initially fairly independent of elevation.
With time and loss of atmosphere, cloud condensation (and thus
precipitation) could occur only at progressively lower altitudes.
Condensation of the Earth's primordial steam atmosphere occurred
-4.0 b.y. ago [7]. Assuming that the martian primordial atmosphere
also condensed at approximately the same time (perhaps sooner
given Mars' distance from the Sun), the maximum interval of time
liquid water existed on the surface is either -1.2 b.y. or-450 m.y.
The differences in these estimates are due to the uncertainties in the
absolute ages of the martian periods and are based on two different
models of the cratering flux at Mars [8.9 respectively].
Because the early Sun is thought to have had a lower luminosity
than today [10], -5 bar of CO 2 may have been needed to maintain
the ancient martian surface temperature above freezing [ 11]. On the
other hand, models incorporating early solar mass loss [12] suggest
that early solar luminosities were actually much higher than today.
This would allow the early martian atmosphere to be much thinner
(-1 bar) and yet warm enough for liquid water. Regardless, the age
and elevation relationship of features contained in the cratered
highlands suggest that the pressure of the martian primordial
atmosphere was never fixed at a high level but steadily decreased to
<1 bar at about the beginning of the Amazonian. If sapping and
seepage of groundwater were the mechanisms for ancient valley
network formation [2] and highland degradation [31, a recharge
mechanism is still needed for the aquifer in order to maintain these
processes over the interval of time they were operating (tens to
hundreds of millions of years at any given elevation). Again, martian
atmospheric pressures must have been maintained > 1 bar for a long
time in order to produce the weather patterns necessary to efficiently
recharge the highland aquifer at higher elevations. Based on the
amount of time fluvial processes occurred on Mars, a rough estinaate
of the primordial atmospheric pressure is -5-10 bar. Possible re-
charge of the atmosphere through impact-induced CO,_ [13] suggest s
that highland degradation may have also been periodic, but such a
mechanism would have become less efficient with time to correlate
with the age/elevation relations of highland features. If the weak
Sun paradox is wrong Jill the primordial atmosphere would still
need to be between -5 and 10 bar initially to allow ancient valley
network formation and highland degradation to occur over the
interval of time observed.
The primordial terrestrial atmosphere and oceans were high-
ly reducing [14]. Similarly, it is probable that Mars also had a
primordial,h ighly reducing atmosphere and surface waters. Possible
release of martian water in a CO,,-rich atmosphere by precipitation
and channel-forming processes has led numerous investigators to
speculate on the creation of massive martian carbonate deposits
[e.g., 11 ]. The formation of such deposits would tend to remove CO_,
from the martian atmosphere and would requ ire a substantially thick
primordial atmosphere (-20 bar [ 11 ]) for ancient valley network and
highland degradation proces ses to operate for-450 m.y. or- 1.2 b.y.
However, these hypotheses have been based on the assumption that
an acidic primordial atmosphere (pH <1-3 [15]) was buffered by
cations released through the weathering of rock. Precipitation of
calcium carbonate occurs only in water with a high pH (>7.8 [16]).
On Earth. precipitation of calcium carbonate did not become a
common phenomenon until the Proterozoic (2.5 b.y.) when stable.
shallow marine cratons developed, thus allowing weathered cations
to concentrate [17]. Simply. terrestrial oceans were in existence
-1.5 b.y. before precipitation of calcium carbonate started to occur,
and even then it was in unique circumstances!
On Mars two scenarios exist for standing bodies of water, the
extreme being Oceanus Borealis [18]. This large ocean, thought to
occupy much of the northern plains, postdates most of the fluvial
features on Mars (up to the middle Amazonian), is needed to explain
https://ntrs.nasa.gov/search.jsp?R=19940017194 2020-06-16T18:38:02+00:00Z
10 Workshop on Early Mars: How Warm and How Wet ?
 iiiiiiilla Nii i ! ! iiii Ni
i!i!ii!ii suaace a ®i
_:_.-'-.:_:._ Water ' n _:_: ::_:::_...... _::
iii:::ili::iiiii R : _911 :i::::::::::-_i:!, iii:_:_:_:_
!::i!_-i::i::i::i::!Regolith _ _:i!i!iiiiiii_ili Regolith i iiiiii!i!'ii
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
N I H A
Fig. 1. A two-box model showing the location of reducing (R) and oxidizing
(O) conditions on Mars through time. Oxidizing conditions in stage I represent
local O oases, which may have developed in small pools formed by precipitation
or seepage. Oxidizing conditions in stage I1 represent buried O oases localed
where goundwater is enriched by volcanics from an evolved mantle. Based on
Fig. 3 in [14].
the formation of putative glacial features in the southern hi_tlands,
and probably did nol exist (see discussion in [ 19]). More realistic are
the_aller, isolated lacustrine basins proposed for low-lying areas
in the rlorthem plains surrounded by outflow channels [20.21 ] and
in the ci'0tered highlands where numerous ancient valley networks
tet'minate [22]. Such basins are suppo_aed by geomorphic evidence
(e.g., poss_Je wave-cut terraces [20,21]) and occur during the
interval that _Sther fluvial features were forming. In addition to these
basins, smallerisolated pools may have developed in topographic
depressions (e.g.. impact craters) if precipitation occun-ed in the
highlands as suggested in [3]. It is especially likely that these
smaller pools allowc:d eroded materials to concentrate, raise the
local pH, and induce the fornaation of carbonates. Such "oases"
could be the most likely-locations of carbonate deposits on Mars.
Other oases may exist underground where oxidizing volcanic gases
interact with groundwater to raise the pH, and may help explain the
presence of carbonates in the SNC meteorites [23]. Based on this
view and the terrestrial example-J14], a "'two-box" model for the
oxidizing stages for Mars is propoffed (Fig. 1).
References: [1] Can- M. H. (1986) Icarus, 68, 187-216.
[2] Pieri D. (1980) Science. 210. 89,_--897, [3] Craddock R. A. and
Maxwell T. A. (1993)JGR. 98, 3453-3468.[4] Tanaka K. L. (1986)
Proc. LPSC 17th. in JGR, 91. EI39-E158. [5] Zimbelman J. R.
et al. (1992) JGR, 97. 18309-18317. [6] Doh m E M. and Scott D. H.
(1993) LPS XX/V, 40 7-,-,-_Y8.[7] Holland H. D.(1984) The Chemical
Evolution of th e Atr, osphere and Ocean, 582, Princeton. [8] Hartmann
W. K. el al. (1981) In Basaltic Volcanism on the TerrestrialPlanets,
1049-1127, Pergamon, New York. [9] Neukum G. and Wise D. U.
(1976) Science. 194, 1381-1387. [10] Gou_ D. O. (198I) Solar
Phys., 74, 21-34. [11] Pollack J. B. et al. (1987) Icarus, 71.
203-224. [12] Graedel T. E. et al. (1991) GRL, 18. 1881-1884.
[13] Cart M. H. (1989)Icarus, 79, 311-327. [14] Kastings J. F.
(1993) Science. 259, 920-926. [15] Ivanov V. V. (1967) Chemisrry
of the Earth's Crust. 2,260, Israel Program for Scientific Transla-
tions, ]eru salem. [ 16] Kru mbein W. C. and Garrels R. M. (1952)J.
Geol., 60, 1-33. [17] Grotzinger J. P. (1989) Spec. Publ. Soc. Econ.
Paleontol. Mineral., 44, 79. [ 18] Baker V. R. et al. (1991) Nature.
352, 589-594. [19] Kerr R. A. (1993) Science, 259. 910-911.
[20] Parker T. J. et al. (1989) Icarus, 82, I 11-145. [21 ] Scott D. H.
et al. (1992) Proc. LPSC Vol. 22, 53--62. [22] Goldspiel J. M. and
Squyres S. W. (1991) Icarus. 89. 392-410. [23] Wright I. P. et al.
(1990) JGR, 95. 14789-14784.
[2
AN ATTEMPT TO COMPREHEND MARTIAN WEATHER-
ING CONDITIONS THROUGH TIIE ANALYSIS OF
TERRESTRIALPALAGONITESAMPLES. C.DouglasLI. P.
WrightL J. B, Bell-', R. V. Morris _, D. C. Golden _, and C. T.
PillingerL _The Open University, Walton Hall, Milton Keynes,
MK7 6AA, UK, -'Mail Stop 245-3, NASA Ames Research Center.
Moffet Field CA 94035-1000, USA, 3NASA Johnson Space Center,
Houston TX 77058, USA.
Spectroscopic observations of the martian surface in the visible
to near infrared (0.4-1.0 pm). coupled with measurements made by
Viking, have shown that the surface is composed of a mixture of
fine-_ained weathered and nonweathered minerals. The majority
:of the weathered components are thought to be materials like since-
tile clays, scapolite, or palagonite [1]. Until materials are returned
for analysis there are two possible ways of proceeding with an in-
vestigation of martian surface processes: (1) the study of weather-
ing products in meteorites that have a martian origin (SNCs) and
(2) the analysis of certain terrestrial weathering products as analogs
to the material found in SNCs, or predicted to be present on the
- marlian surface. Herein, we describe some preliminary measure-
menls of the carbon chemistry of terrestrial palagonite samples that
exhibit spectroscopic similarilies with the martian surface [2-4]..
The data should aid the understanding of weathering in SNCs and
comparisons between terrestrial palagonites and the mat'tian sur-
face.
TI_eSNC meteorites contain a variety of weathering products
inclu_ling carbonates, sulphates, and clays of martian and terrestrial
origin [527]. The C chemistry of SNC meteorites has already been
studied extefisively so it would seem reasonable to characterize the
nature of C in i_rreslrial palagonites with a view to comparing the
data with the results from SNC meteorites [6]. Several mechanisms
for the formation of palagonites (which are hydrated and devitrified
basaltic glasses) have been proposed: (1) hydrothermal alteration
(induced by volcanism, geothei-mal _m'adients, or impact). (2) sub-
permafrost ma__naatic intrusion. (3) subaerial intrusion above the
permafrost layer, and (4) static gas-solid weathering [8].
As aprelimlnaryinvestigation, twoterrestrial palagonite samples
have been analyzed for C stable isotopes by the use of stepped com-
bustion and static mass spectrometry. One, PN-9, collected from
Mauna Kea, is a palagonitic soil and has been studied extensively
because its infrared absorption features closely resemble that of the
martian surface [2,5,9]. The C released between room temperature


The early Martian environment: Clues from the cratered highlands and the Precambrian Earth

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server