NEEP602 Course Notes (Fall 1997)
Resources from Space
Lecture #16: Little Green Persons!
Title: Life on Mars?
NOACHIAN SYSTEM 1.BEGINNING---------------------------------------------4.57 b.y. 2.MAGMA OCEAN/PLANETARY DIFFERENTIATION-----------------4.5-4.4(?) b.y. 3.CRATERED UPLANDS/CLAY SOUP ---------------------------4.4(?)-4.2(?) b.y. HESPERIAN SYSTEM 4.LARGE BASINS------------------------------------------4.2(?)-3.9 b.y. 5.PLANETARY VOLCANISM ----------------------------------3.9-2.0(?) b.y. AMAZONIAN SYSTEM 6.MATURE CRUST/ATMOSPHERE-------------------------------2.0(?) b.y.-PRES.
- If life comparable to simple forms present on Earth were to devlop
on Mars, the critical period of Martian evolution would be those between
Stages 2 and 5, above. The discussion notes below are added within the
context of the more general notes of Lecture 14.
3. Cratered Uplands/Clay Soup - 4.4(?)-4.2(?) b.y.
- Highly cratered crust similar to lunar highlands.
- Formation of a megaregolith to about 10 km similar to the 25 km thick megareglith of the Moon.
- Probable dense, moist, CO2 rich atmosphere with significant
CH4, CH4 derived areosols, and NH4 (Sagan
and Chyba, 1997, and Kasting, 1997)
- Note: The nature and evolution of the Martian atmosphere through time
consists of many uncertainties, including the following (see Carr, 1996,
- Initial composition
- Potential of a late infall of water-rich (cometary) material [not likely based on comparison of D/H rations of Earth's water with that measured for comets Hale-Bopp and Hyakutake (Owen ,T., and Meier, R., 1997, reported in Science, 277, 318)]
- Variability of obliquity of rotational axis to orbital plane
- Changes in insolation
- Changes in composition due to core fromation and evolution of hydrogen and other volatiles from the interior
- Changes in composition due to weathering of the megaregolith
- Changes in composition due to magmatic and hydrothermal activity
- Amount and stability of greenhouse gases (NH4, CH4, CO2, H2O) through time
- Degree of CH4 derived organic aerosol formation by photolysis (Sagan and Chyba, 1997, and Kasting, 1997)
- Amount and rate of surface regolith carbonate decompostion due to UV radiation (Mukhin, et al, 1996).
- Degree of impact erosion through the Large Basin Stage, see below.
- Degree of hydrodyamic entraining by high rates of hydrogen escape.
- Strength of the magnetic field, if any.
- Degree of solar wind erosion (sputtering) (Kass and Yung, 1995, and Johnson, and Liu, 1996)
- Degree of water and carbonate capture and recycling in the megaregolith
- Note: The nature and evolution of the Martian atmosphere through time consists of many uncertainties, including the following (see Carr, 1996, Chapters 5-7):
- Probable creation and continual impact stiring of a soupy mixture of
water, clay , carbonate, hydrocarbons and other atmospheric and crustal
- Note: This probably is the most likely period for the "evolution"
of complex organic molecules as precursors to replication life (possibly
self replicating RNA (see Ekland and Bartel, 1996, and Science, 1996, 273,
870-872) for the following reasons:
- Terrestrial isotopic fractionation of biological origin has been dated at 3.850 b.y. (Mojzsis, et al, 1996) and the development of molecular precursors must significantly predate this date.
- Clay mineral sturctures (montmorillonite, illite, and hydroxylapatite) have been shown to serve as templates for complex organic molecules (Ferris, 1996)
- Necessary phosphate compounds can be produced and preserved during impacts into relatively cool crustal materials like a clay soup and also have been found in the Muchison meteorite along with other organic compounds (Science, 1996, 273, 870-872).
- Aqueous slurries of coprecipitated NiS and FeS, possible hydrothermal mineral species in reducing crustal environments such as deep sea smokers on Earth, converted CO and methanethiol (CH3SH and detected in volcanic and ancient gases on Earth) through several steps to methyl thioacetate (CH3CO(SCH3) plus H2S. With its C-C bond, methyl thioacetate resembles acetyl-coensyme A which is a candidate for a primordial initiation reaction for a chemoautotrophic origin of life (Huber and Wachtershauser, 1997, and Crabtree, 1997)
- Impact shock in a CH4, H2O, CO2, N, and H2S containing, attmosphere produces a variety of organic compounds (see McKay and Borucki, 1997)
- Note: This probably is the most likely period for the "evolution" of complex organic molecules as precursors to replication life (possibly self replicating RNA (see Ekland and Bartel, 1996, and Science, 1996, 273, 870-872) for the following reasons:
- 4. Large Basins - 4.2(?) - 3.8 b.y.
- Note: valley networks appear to have formed by ground water sapping in the upper megaregolith (Carr, 1996), possibly sustained by increasing hydrothermal activity in response to remelting of the mantle under the Uplands. Such sapping and the accompaning mass wasting of the upper megaregolith downstream would have carried any organic compounds toward the basins. The movement of magmas into the weathered megaregolith would potentially recycle meteoric water and CO2, producing much hydrothermal activity and recycling of atmospheric volatiles thus counteracting atmospheric losses.
- Terrestrial isotopic fractionation of biological origin has been dated at 3.850 b.y. (Mojzsis, et al, 1996)
- Complex, evolving, single cell life forms known as fossils on Earth at 3.55 b.y. (Schopf, 1993)
- RNA appears capable of at least some self replication (Ekland and Bartel, 1996)
Summary arguments for early life
- Great age (>3.55 billion years) of earliest one cell life forms on Earth and of isotopic evidence of biological processes (3.850 b.y.).
Large basin formation largely in present northern hemisphere.
Note: multicell life forms would probably not survived these large events, but the complexity of their precursors may have been enhanced by the energy, shock chemistry, and material introduction.
Present rotational dynamics and variability established.
Note: These established an inherently extreme variability to climate variations unlike that experienced by Earth. Such variability may have inhibited the survival of some replicating forms but may have acted as a forcing factor on "speciation" of others.
Much of megaregolith concentrated in southern hemisphere.
Note: Clay-related synthesis of complex organic molecules may have made the Uplands a reservoir of organic building blocks for more complex evolutionary activity in flooded basins (see below).
Remelting of the warming mantle beneath the large basins may have been triggered by the release of lithostatic pressure.
Upland valley networks (see Carr, 1996, Chapter 4) formed late in this stage.
Organization of complex organic molecules into replicating life forms, if it occurred on Mars, probably happened at or near the end of this stage for the following reasons:
- Evidence of an environment that allowed surface subsurface water to exist.
- Implications of the model for lunar evolution on the nature of the surface environment of terrestrial planets when self replicating organic compounds (life) first formed, that is, intense cratering with production and weathering of fine-grained and glassy material in a water and carbon dioxide rich megaregolith, addition of extraplanetary material, and repeated peaks of high thermal energy.
- Other planetary systems apparently capable of retaining liquid water, such as, 70 Virginis in the constellation Virgo (Science, v 271, 449-450)
- Various experimental results increasingly suggests complex organic chemistry is possible in potenial Martian environments between 4.4 and 3.8 b.y.
Questions to be answered
- For how long and how frequently did surface water exist?
- What overall environmental conditions existed at that time?
Arguments against present life on Mars
- Some Viking analyses gave no suggestion of biological metabolism occuring in Martion soil. (Horowitz, 1988)
- Present surface environment incompatible
Arguments for present life on Mars
One Viking analysis was consistant with poistive results of the same experiment in the dry valleys of Antarctica (Levin, 1988)
Potential ecological niches related to permafrost, subsurface weathering, and active hot springs, if present.
Relevant terrestrial niches (see Ghiorse, 1997, Fredricson and Onstott, 1996, and Monastersky, 1997)
Algae in brines of Antarctic pack ice (Arrigo, K., 1997)
Bacterial in----500 meters below the surface in South Carolina (Wobber, F.J., et al, 1989, reported in Science News, 151, 192)
Bacterial in old bearing conglomerates at 60oC, 3.5 km below the surface in South Africa (Onstott, T. C., reported in Science News, 151, 192)
Bacteria in sedimentary rocks 600m below the surface (340 m.y.)
Bacteria (Bacillus infernus) in volcanic springs at 75oC in Yellowstone National Park and in deep ocean vents
Bacteria 2.7 km below the surface (Phelps, T.J., et al, 1996, AGU December meeting reported in Science News, 151, 192)
Bacteria in basalt 1.5 km below the surface in Washington living on carbon dioxide and hydrogen from weathering of basalt (80-160 m.y.) (Stevens and McKinley, 1995)
Bacteria in sandstone and shale in New Mexico (DOE team, 1997, Nature, March 6)
Bacteria and archeaea in granite 207m below the surface in southeast Sweden ((Pedersen, et al, 1997)
Various in hydrothermal vents in the deep sea
Bacterial spores (Bacillus sphaericus) in amber encased bee (25-40 m.y.) (Cano and Borucki, 1995)
Chemoautotropic bacteria in a limestone cave ecosystem living on carbon and H2S in southern Romania (Sarbu, et al, 1996)
Bacteria on bottom of sea ice at the poles (Staley, J.T., as reported in Science News, 149, 126)
Fungi, if evolved, and lichen colonies both have proved on Earth to be geologically resilient in the extreme (Visscher, 1996, and Levin, 1988)
Search for evidence of life on Mars (see Gould, 1994)
- Field geological search for fossil-bearing strata in channels cut in layered sediments.
- Drilling search for subsurface ecological niches.
- Search under the edges and in strata of the ice caps.
- Search for hot springs and volcanic alteration zones.
- Examine valley network exposures in the Upland megabreccia for molecular fossils
Evidence for large volumes of water and water ice (Carr, 1996, Chapter 7)
- More than 3.8 b.y. ago (Noachian cratered uplands at elevations greater
than +1 km)
- Valley networks of converging tributaries suggest ground water "sapping" at the heads of drainages.
- Mass wasting rather than running water.
- Less than 3.8 b.y. ago (Hesperian plains at elevations less than -1
- Outflow channels
- Catastrophic floods at 100 times peak discharges of terrestrial floods
- release of ground water or rapid melting of ground ice in the megaregolith
near the edges of large basins
- evidence of carbonate and mineral salt solution
- as much a 105 km3 of water released
- volcanic activity, faulting, and/or impacts may have triggered some floods
- release of ground water or rapid melting of ground ice in the megaregolith near the edges of large basins
- Catastrophic floods at 100 times peak discharges of terrestrial floods (109 m3/s)
- rhythmically layered sediments observed up to 8 km thick and 6x105 km3
- "patterned ground"
- polar caps
- Outflow channels
- glacial features
- "patterned ground"
- How much water might there have been?
- Geological estimates range between 10 m and 1 km 9Carr. 1996, p167)
- How much is there today if spread over entire planet?
- Martian atmosphere - minute
- Martian poles - less than 0.03 km
- Martian megaregolith - 0.5-1.4 km if all pore spaces filled
Other potential resource concentrations on Mars besides water
- Sorting of heavy minerals from sand and gravel by water
- Sorting of clays from sand by wind
- Sorting of clays from sand by settling rates in lakes (layered sediments)
- Chemical evaporite precipitates of carbonate, iron oxides, and various salts in lakes
- Metal sulfide precipitates in lake beds
- "Black smoker" sulfide deposits in lake beds
- Hydrothemal veins of metal sulfides and carbonates near volcanos
- Hydrothermal deposits veins and disseminated deposts in the megaregolith of the Uplands
Composition of the soil
Martian soils have been largely but not entirely homogenized by dust storms (see Lecture 15), howver some differences have been noted between the Viking sites and Pathfinder"s site.
- Minerals related to weathering or alteration observed in the SNCs
- clays (montmorillonite)
- hydrated iron oxides
- Mg and Fe carbonates (Treiman, 1996)
- iddingsite (clay and iron oxide mixture) ( Swindel, 1997)
- Carbonates may be largely absent from the surface regolith down to several meters due to UV induced decomposition (Mukhin, 1996)
|The figure summarizes what we know about the evolution of Mars and appears to be consistent with the best information and ideas availabe to date. Stay tuned!|
1. Discuss the rationale, if any, to assume that simple life forms developed on Mars and that they may have evolved to survive in some ecological niches to the present time.
2. Where would you go to search for fossils and current life forms on Mars and why?
Mars environment material
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