concepts of life and biosignatures in the contexts …...concepts of life and biosignatures in the...
TRANSCRIPT
Concepts of Life and Biosignatures in the Contexts of Mars
and Mars-analog Environments
David J. Des Marais NASA Ames Research Center
information storage and replication
energy harvesting and transduction
organic biosynthesis
EVOLUTION
Research in Mars-Analog EnvironmentsExamples of Key Challenges
• Concepts of life: Earth-centric, Mars-relevant, truly universal
• Habitable environments: resources, conditions, duration, “envirosignatures”
• Biosignatures: biological “signals” vs environmental “noise,” potential vs definitive biosignatures
• Preservation: Biological primary production vs rates of destruction and preservation, preservation media, taphonomy
• Focus on processes that are directly relevant to environments on Mars (past or present)
Evolution (descent with modification)
Lightand/orReactants
Heatand/orProducts
CO2
InformationStorage and Replication
EnergyHarvesting and Transduction
OrganicBiosynthesis
Life'sBasicFunctions
OrganicMatter
Life’s Basic Functions
, CH4, CO, etc.
Habitable Environments
Martian Deposits Indicating the Former Presence of Aqueous Environments (Murchie et al., 2009)
theiikian siderikian
Amazonian Hesperian Noachian
clays sulfates anhydrous ferric oxides
Geologic Eras
phyllosian
Layered phyllosilicates
Phyllosilicate in fans
Plains sediments ?
Meridiani layered Valles layered
Layered Hydrated Silica
? Gypsum plains ? ? ?
Deep phyllosilicates
Proposed Chemical Environments
Carbonate deposits
Intracrater clay-sulfates ?
Chloride Deposits
Coupled mineralogy and morphology define aqueous environments Their character has evolved, indicating changing environments How should we prioritize these environments during landing site selection? “So many places, so few landed science missions!”
ODY, MEX, MRO
3.8 to 3.6
3.3 to 2.8
Approximate age, billions of years
Tosca et al., 2008
Archaea
Eukarya
Archea in halite, Earth
solutes
demand supply
extremes impose costs
solubility
Habitable Environments
Note: Several examples of “classic” extreme environments tend to have ‘only’ one or two extreme parameters….
MMineralogical Traces of Early Habitable EnvironmentsWater (availability, activity, composition), Energy (level,
flux), Temp., pH, Salinity
Energy balance analysis
Energy Demand = f (T, pH, fluid comp.,
self-repair)
Energy Supply = f (T, pH, fluid comp.,
& host matrix)
(these factors combine to determine how habitable a system may be)
Extremes in T, pH, salinity, radiation, etc. impose substantial energy demands
(T. Hoehler, 2011)
What are the “ultimate” environmental boundaries for life… on Earth? on Mars? beyond?
A biosignature is an object, substance and/or pattern whose origin specifically
requires a biological agent.
The usefulness of a biosignature is determined not only by the probability of life creating it, but also by the improbability of
nonbiological processes producing it.
Biosignature
Evolution (descent with modification)
Lightand/orReactants
Heatand/orProducts
CO2
InformationStorage and Replication
EnergyHarvesting and Transduction
OrganicBiosynthesis
Life'sBasicFunctions
OrganicMatter
Life’s Basic Functions
, CH4, CO, etc.
Fossil Biosignatures: What We Look For…
-1.0-2.0-3.0-4.0-4.0-70
-60
-50
-40
-30
-20
-10
0
10
20
C13δ
Carbon Isotopic Recordin Sedimentary Carbonates and Organic Matter
Age, Ga
Organics
OxidizedPaleosols
BIFDisappear
Carbonates
Body Fossils
Biominerals
Biofabrics
ChemicalFossils
(Biomarkers)
Stable Isotopes
Recognizing Biosignatures in Deep Time and Space
• Many biosignatures from recent geologic epochs are easily contrasted from abiotic features.
• But modern biosignatures arose after billions of years of evolution.
• In early geologic records the boundaries between biotic and abiotic features are far less distinct.
• Perhaps NO sharp distinctions existed between prebiotic features and biosignatures during the transition from the prebiotic realm to the biosphere.
Features created by life
Biosignatures: featurescreated ONLYby life
FeaturescreatedONLY bynonbiologicalprocesses
Ambiguous features
Cell-like morphologiesOrganic matter, sedimentaryRock micro- & macrofabricsMinerals, some morphologiesStable isotopic patterns
Crustal C inventoryBulk crustal oxidation stateThermo-&radiochem. productsMinerals: ign.,met.&most sed.Isotopic equilibria, most
Features created by nonbiological processes
“SIGNAL” / “NOISE”
Compound class fatty acids S membranes, cells O M.W. distribution n-C16 to n-C18 P isoprenoids S permeability Complex molecules S enhanced functions Stable isotopes P metabolism ecology
Lipid biosignature features & functions
Biosignature type: Object Pattern Substance
Mineral Diversity on Earth vs Age (R. Hazen)
Research in Mars-Analog EnvironmentsExamples of Key Challenges
• Concepts of life: Earth-centric, Mars-relevant, truly universal
• Habitable environments: resources, conditions, duration, “envirosignatures”
• Biosignatures: biological “signals” vs environmental “noise,” potential vs definitive biosignatures
• Preservation: Biological primary production vs rates of destruction and preservation, preservation media, taphonomy
• Focus on processes that are directly relevant to environments on Mars (past or present)
6/8/16 222020 Mars Rover Science Definition Team
Scientific Process for Detecting Past Martian Life
BIOSIGNATURE PRESERVATION
POTENTIAL
Past conditions suitable for the existence of life at the site.
Past conditions suitable for the preservation of past life in the geologic record.
An observable feature that might be evidence of past life.
DEFINITIVE
An observable feature that is confirmed to be evidence of past life.
Proposed Mars 2020 Rover
Labs on Earth MSR
HABITABLE ENVIRONMENT
To search for potential biosignatures, it is necessary to (a) identify sites that very likely hosted past habitable environments, (b) identify high biosignature preservation potential materials to be analyzed for potential biosignatures,
and (c) perform measurements to identify potential biosignatures or materials that might contain them.
End
image by David Deamer