David J. Des MaraisNASA Ames Research Center

Early Mars ?

Preservation of Evidence of Ancient Environments and Life on Mars

Mars today

Key factors affecting biosignature preservation & abundance

Paleo-productivity

Transport and burial

Sedimentary redox (Oehler’s talk)

Mineralogy

Lithification

Subsequent alteration / destruction

Preservation on Mars

Noachian-Hesperian environments & processes: major consequences for basic habitability factors

Persistence of ancient aqueous environments

Nature of deposits in Noachian aqueous environments

Phyllosilicate deposits & organic matter concentrations

Preservation potential of the four “finalist” MSL sites

Importance of Age

Meridiani Planum and the Global Hydrology of Mars *

* Andrews-Hanna et al. (2007)

A

B

A

B

detected evaporite deposits

Importance of Elevation

Stream Systems

Stepinski & Luo, LPSC41, 2010

Deltas

Di Achille & Hynek, LPSC41, 2010

Gusev CraterGusev Crater~180 km diameter~180 km diameter

ApollinarisApollinarisPateraPatera

(volcano)(volcano)NorthernNorthernLowlandsLowlands

SouthernSouthernHighlandsHighlands

Ma’AdimMa’AdimVallisVallis

x

Orbiter view (MRO HiRISE)

Husband

Hill and

InnerBasin

ground view

(MER Pancam)

Vesicular basalts: water-rich magmaExplosive volcanism: volatile-richBomb sag: bomb impacting wet sedimentFerric sulfate-rich deposits: hydrothermal/fumarolic/acidicPure silica: sinter/acid leachingCarbonate rich bedrock

Importance of Age and Depth in Crust

MSL Science Team Field Site Discussions – Mawrth

Oyama(107 km diam)

candidate MSL field site

“Mawrth mouth”

regolith covers bedrock

in the ‘intermediate gray’

areas – some of that

regolith is considered to

be eolian-deposited dust

and/or crusted eolian

dust (e.g., Presley and

Arvidson 1987)

bedrock exposures have a light tone;some dark-toned materials in this area are also bedrock (commonly but not always a caprock above light-toned rocks)

note Oyama formed in light-toned bedrock

Note: Candidate landing ellipse size and shape is approximate.

The name “Oyama” was approved by the IAU 26 March 2010.Named for Vance I. Oyama, Viking Gas Exchange Experiment PI.

MG

S M

OC

re

d w

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an

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mo

saic

Subaqueous? : near margin of crustal dichotomy, low elevation, phyllosilicatesCrust stabilized in Hadean, later incision by channel, burial, re-exumationHence, potentially good preservation of any paleobiological featuresBUT: Noachian section impact-fractured: sedimentary features hard to see from orbitYET, if shock effects are localized, local survival of paleobiological features possibleDeposits reflect key aspects of Hadean, e.g., impacts, volcanism, aqueous processes Shares attributes with Earth’s Archean deposits preserving paleobiological information

Mawrth Vallis

Pilbara Craton and Hamersley Range, W. Australia

Pilbara igneous domes and greenstones, and Hamersley Range~Coastal marine setting: “at margin of crustal dichotomy”Craton stabilized in archean, low later tectonic activity mimics low martian tectonicsHence, remarkable preservation of paleobiological featuresBUT Archean section deformed by tectonic activity, overlain by less-deformed deposits SO older aqueous sedimentary features are hard to discern from orbitYET deposits reflect key Archean and Paleoproterozoic environments

Mars Global Surveyor MOLA Topography

Marine Chlorophyll Abundances (Low Moderate High)

Key Factors:Paleo-productivityTransport & burialSedimentary redoxMineralogyLithificationLater alteration

Pilbara Craton and Hamersley Range, W. Australia

“Discouraging” evidence of tectonic and thermal activity YET well-preserved deposits from habitable environments exist However wide range of organic concentrations and preservation is seen So how can we assess key preservation factors from orbit?

Eberswalde

GaleMawrth

Holden

- 2.2 km

- 2.3+ km

- 1.5 km

- 4+ km

Preservation of Evidence about Ancient Mars

Noachian-Hesperian environments and processes

Persistence of ancient aqueous environments

Noachian deposits in aqueous environments

Phyllosilicate-rich deposits and organic matter contents

Preservation potential of the four “finalist” MSL sites

Age of deposits: mid-Noachian to early Hesperian Water persistence: effects of elevation and geologic age

Allochthonous vs autochthonous phyllosilicates (Kennedy work, redox state, nature of organics [e.g., plant lignin can survive transport; can microbial components?])

Redox state of deposit Lithification: rate and extent