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