Habitability Bonnie Meinke January 27, 2009 Bonnie Meinke January 27, 2009

HabitabilityHabitability

Bonnie MeinkeJanuary 27, 2009

Bonnie MeinkeJanuary 27, 2009

IntroductionIntroduction

Define Habitability The Habitable Zone Environment of early Earth

Define Habitability The Habitable Zone Environment of early Earth

Defining HabitabilityDefining Habitability

What do we mean when we say habitable? Earth-like animal life: specific

requirements

Microbial life: broader set of conditions


requirements

Microbial life: broader set of conditions

Defining Habitability

Defining HabitabilityDefining Habitability


requirements (oxygen, water, dry land, temperature range)

Microbial life: broader set of conditions (more extreme conditions ok)


requirements (oxygen, water, dry land, temperature range)

Microbial life: broader set of conditions (more extreme conditions ok)


Common basic requirements for life

Common basic requirements for life

Water Stable climate

Water Stable climate


What stabilizes the climate?

What stabilizes the climate?

Size - long-term heat source Stellar evolution - incoming solar

energy Impact rate - could result in climate

change Presence of large, natural satellite -

prevents large swings in obliquity Oceans - regulate global

temperatures

Size - long-term heat source Stellar evolution - incoming solar

energy Impact rate - could result in climate

change Presence of large, natural satellite -

prevents large swings in obliquity Oceans - regulate global

temperatures


Habitable ZonesHabitable Zones

Why is Earth the only (as far as we know) habitable planet in our solar system?

2 main properties:Abundant liquid water Environmental conditions that

maintain liquid water

Why is Earth the only (as far as we know) habitable planet in our solar system?

2 main properties:Abundant liquid water Environmental conditions that

maintain liquid water

The Habitable Zone

Liquid WaterLiquid Water

Required temperature: 273-373 K Use this as simple requirement for

identifying possibly habitable planets

Where do planets in this temperature range orbit?

Required temperature: 273-373 K Use this as simple requirement for

identifying possibly habitable planets


The Habitable Zone

Liquid WaterLiquid Water


Called the Habitable Zone

Let’s work it out…


Called the Habitable Zone

Let’s work it out…

The Habitable Zone

How does star type affect HZ?


Different sized stars have different luminosities

T L1/4

Brighter stars have HZs farther out

Different sized stars have different luminosities

T L1/4

Brighter stars have HZs farther out

The Habitable Zone



Main sequence (MS) stars have different luminosities throughout their lifetimes

Continuously Habitable Zone: maintains conditions suitable for life throughout MS lifetime of star

Main sequence (MS) stars have different luminosities throughout their lifetimes

Continuously Habitable Zone: maintains conditions suitable for life throughout MS lifetime of star

The Habitable Zone

Is it that simple?Is it that simple?

Albedo, a

Atmosphere - what part of spectrum can pass through

Albedo, a

Atmosphere - what part of spectrum can pass through

The Habitable Zone

Moves HZ inwards

Moves HZ outwards

Moves HZ inwards

Moves HZ outwards

Role of the Carbon CycleRole of the Carbon Cycle

Kasting proposed the Carbon Dioxide Thermostat Extends to HZ for

Earth-like planets Keeps off

temperature extremes

Kasting proposed the Carbon Dioxide Thermostat Extends to HZ for

Earth-like planets Keeps off

temperature extremes

Carbon sources: Volcanic

outgassing Decarbonation Organic carbon

Carbon sinks: Calcium

carbonate formation

Photosynthesis

Carbon sources: Volcanic

outgassing Decarbonation Organic carbon

Carbon sinks: Calcium

carbonate formation

Photosynthesis

The Habitable Zone

Role of the Carbon CycleRole of the Carbon Cycle

The Habitable Zone

Continuously Habitable Zone

Continuously Habitable Zone

Inner edge: 0.95 AU

Outer edge: 1.15 AU

Inner edge: 0.95 AU

Outer edge: 1.15 AU

Were other planets habitable in the past?

Will other planets be habitable in the future?

Were other planets habitable in the past?

Will other planets be habitable in the future?

The Habitable Zone

Mars: Once Habitable?

Still Habitable?

Mars: Once Habitable?

Still Habitable? Early Mars

Evidence of large amounts of flowing liquid water

Warmer temperatures: Heat from interior

would have been higher

Warm climate from greenhouse gases or CO2 clouds

Early Mars Evidence of large

amounts of flowing liquid water

Warmer temperatures: Heat from interior

would have been higher

Warm climate from greenhouse gases or CO2 clouds

Current Mars Gullies may be

due to underground water

Carbon cycle not as active as on Earth

Current Mars Gullies may be

due to underground water

Carbon cycle not as active as on Earth

The Habitable Zone

Characteristics that make a habitable planet

Characteristics that make a habitable planet

The Habitable Zone

•Other Heat sources to sustain liquid water

•Geothermal•Iceland

•Tidal•Europa

•Other Heat sources to sustain liquid water

•Geothermal•Iceland

•Tidal•Europa

•Size of planet•Internal heat comes from

•Accretional heat•Differentiation•Radiogenic decay

•Allows for plate tectonics

•Mars cooled quickly, so no plate tectonics at present

•Size of planet•Internal heat comes from

•Accretional heat•Differentiation•Radiogenic decay

•Allows for plate tectonics

•Mars cooled quickly, so no plate tectonics at present

Characteristics that make a habitable system

Characteristics that make a habitable system

Star Type: stable luminous stars necessary Sufficiently long

lifetime for life to evolve

Large enough so planets don’t tidally lock

Star Type: stable luminous stars necessary Sufficiently long

lifetime for life to evolve

Large enough so planets don’t tidally lock

The Habitable Zone

•Star system•Single star: allows for stable orbit•Binary system:

•Fewer stable orbits exist•HZ calculated on individual basis

•Star system•Single star: allows for stable orbit•Binary system:

•Fewer stable orbits exist•HZ calculated on individual basis

Characteristics that make a habitable neighborhoodCharacteristics that make a habitable neighborhood Galactic Habitable Zone

Area of high metallicity (elements w/ Z>2) Outer region of galaxy

Lower stellar density Lower radiation levels

Galactic Habitable Zone Area of high metallicity (elements w/ Z>2) Outer region of galaxy

Lower stellar density Lower radiation levels

The Habitable Zone

Early EarthEarly EarthEarly EarthEarly Earth

Astr 3300September 16, 2009

Astr 3300September 16, 2009

Environment of early EarthEnvironment of early Earth

• Evidence of a habitable planet 3.8 Ga– Geological evidence near Isua,

Greenland– Limestone and sandstone– We can infer presence of liquid water– Earth must have had temperatures

similar to today’s

• Evidence of a habitable planet 3.8 Ga– Geological evidence near Isua,

Greenland– Limestone and sandstone– We can infer presence of liquid water– Earth must have had temperatures

similar to today’s

Early Earth

Liquid water 3.8 Ga?Liquid water 3.8 Ga?

• Faint young Sun– Sun was 25-30% less luminous– Simple energy balance shows Earth’s

surface temperature would have been below 273 K

• Other heat sources– Geological activity

• More internal heat from radioactive decay and primordial heat

• Plate tectonics release CO2 - greenhouse traps heat

• Faint young Sun– Sun was 25-30% less luminous– Simple energy balance shows Earth’s

surface temperature would have been below 273 K

• Other heat sources– Geological activity

• More internal heat from radioactive decay and primordial heat

• Plate tectonics release CO2 - greenhouse traps heat

Early Earth

Snowball EarthSnowball Earth

• Global glaciations brought on by disruptions in the carbon cycle– Up to 4 occurred between 750 Ma and 580 Ma ago– Geological record shows layered deposits in tropics

attributable to glacial erosion

• CO2 sinks would cease, but sources would continue. 350 times current CO2 levels would accumulate to create a severe greenhouse, causing the ice to melt w/in a few hundred years.

• All eukaryotes today are from the survivors of snowball earth

• Global glaciations brought on by disruptions in the carbon cycle– Up to 4 occurred between 750 Ma and 580 Ma ago– Geological record shows layered deposits in tropics

attributable to glacial erosion

• CO2 sinks would cease, but sources would continue. 350 times current CO2 levels would accumulate to create a severe greenhouse, causing the ice to melt w/in a few hundred years.

• All eukaryotes today are from the survivors of snowball earth

Early Earth

Early HydrosphereEarly Hydrosphere

How did Earth get all it’s water?How did Earth get all it’s water?

Early Earth

Origin of Earth’s WaterOrigin of Earth’s Water

• Delivered by comet impact– D/H ratios of comets are not the same as on earth– This is unlikely the delivery mechanism

• Solar nebula– Unlikely because relative abundance of other

volatiles are higher in the solar nebula than in planetary atmospheres

• From un-degassed interiors of planetary embryos– Most likely scenario– Hydrated minerals could form around 1 AU

• Delivered by comet impact– D/H ratios of comets are not the same as on earth– This is unlikely the delivery mechanism

• Solar nebula– Unlikely because relative abundance of other

volatiles are higher in the solar nebula than in planetary atmospheres

• From un-degassed interiors of planetary embryos– Most likely scenario– Hydrated minerals could form around 1 AU

Early Earth

Origin of Earth’s Atmosphere

Origin of Earth’s Atmosphere

• Only trace amounts of oxygen for the first 1 billion years– O2 resulted from

breakdown of water vapor by UV radiation

• Current atmosphere is oxygen-rich, so where did it come from?

• PHOTOSYNTHESIS!– First developed in

cyanobacteria 3.8-2.5 Ga ago (Archaean era)

• Only trace amounts of oxygen for the first 1 billion years– O2 resulted from

breakdown of water vapor by UV radiation

• Current atmosphere is oxygen-rich, so where did it come from?

• PHOTOSYNTHESIS!– First developed in

cyanobacteria 3.8-2.5 Ga ago (Archaean era)

Early Earth

Banded Iron FormationsBanded Iron Formations

• Geologic evidence for appearance of free oxygen are Banded Iron Formations (BIFs)

• BIFs provide clues as to the oxidation state of ocean and atmosphere at time of formation

• Usually formed in shallow seas - oxygen available here

• Geologic evidence for appearance of free oxygen are Banded Iron Formations (BIFs)

• BIFs provide clues as to the oxidation state of ocean and atmosphere at time of formation

• Usually formed in shallow seas - oxygen available here

Early Earth

Role of hydrothermal systems

Role of hydrothermal systems

• Seawater flowing through hydrothermal vents dissolved iron

• Injected iron into deep ocean through vents

• Deep ocean too oxygen-poor to oxidize iron, so it cycled through system to be deposited in shallow seas.

• Possible iron was consumed by bacteria near vents and transported in drifts of large colonies

• Seawater flowing through hydrothermal vents dissolved iron

• Injected iron into deep ocean through vents

• Deep ocean too oxygen-poor to oxidize iron, so it cycled through system to be deposited in shallow seas.

• Possible iron was consumed by bacteria near vents and transported in drifts of large colonies

Early Earth

Evidence for early life on Earth

Evidence for early life on Earth

• Stromatolites– Oldest known is

3.46 Ga-old– Formed from

cyanobacteria and blue-green algae

– Organisms for gelatinous mat and precipitate calcium carbonate, so it looks like stack of pancakes w/ alternating layers

• Stromatolites– Oldest known is

3.46 Ga-old– Formed from

cyanobacteria and blue-green algae

– Organisms for gelatinous mat and precipitate calcium carbonate, so it looks like stack of pancakes w/ alternating layers

Early Earth

Carbon IsotopesCarbon Isotopes

• Can be used as indicators of biological processes

• Can be used as indicators of biological processes

Early Earth

• 12C and 13C are stable isotopes

• Ratio is affected by physical processes

• More energy efficient to make or break 12C bonds

• 12C is preferentially incorporated into products of chemical reactions

• 12C and 13C are stable isotopes

• Ratio is affected by physical processes

• More energy efficient to make or break 12C bonds

• 12C is preferentially incorporated into products of chemical reactions

Carbon IsotopesCarbon Isotopes

• A negative value can be used as a biomarker, indicating fractionation is due to photosynthesis


Early Earth

• Isotopic fractionation

• let’s work it out

• Isotopic fractionation

• let’s work it out€

δ13C =13C

12Csample

13C12Cs tan dard

−1 ⎡ ⎣ ⎢

⎤ ⎦ ⎥×1000

Evolving ComplexityEvolving Complexity

• Ediacaran fauna show distinctive changes in size ~670 Ma ago)


Early Earth

• Life started small (maximum of a few mm in size)

• In the last 600 Ma, evolution of more larger, more complex organisms has occurred

• Life started small (maximum of a few mm in size)

• In the last 600 Ma, evolution of more larger, more complex organisms has occurred

Evolving ComplexityEvolving Complexity


• Tubular, frond-like, radially symmetric

• cm-m in size


• Tubular, frond-like, radially symmetric

• cm-m in size

Early Earth

Increase in size and diversity

Increase in size and diversity

• Subsequently, after 500 Ma ago, sizes increased 2 orders of magnitude

• Dinosaurs• Larger mammals

• Subsequently, after 500 Ma ago, sizes increased 2 orders of magnitude

• Dinosaurs• Larger mammals

Early Earth

Major extinctionsMajor extinctions

• Marked periods of Earth’s biological history

• Reduce diversity• Most recent

– Possibly due to comet or asteroid impact– Die out of the dinosaurs (65 Ma ago)

• Demonstrates how important “environmental stability” is for a habitable planet

• Marked periods of Earth’s biological history

• Reduce diversity• Most recent

– Possibly due to comet or asteroid impact– Die out of the dinosaurs (65 Ma ago)

• Demonstrates how important “environmental stability” is for a habitable planet

Early Earth

Banded-Iron Formations (BIFs)

• Most formed 3Ga-1.8Ga

• Amount of Oxygen locked in BIFs is ~20 times the volume in the modern atmosphere


• Formation:– Oxygen produced by cyanobacteria combined with

iron in the ocean (early ocean was acidic and iron-rich)

– Oxidized iron then deposits in a layer– Process is cyclical due to oscillating availability of

free oxygen– Eventually, photosynthesis caught on, the oceans

because well-oxygenated, and the available iron in the Earth's oceans was precipitated out as iron oxides


• Snowball Earth cycles may have been the cause of bands– During snowball periods, free oxygen not available

and iron– Followed by oxidizing periods of melt

• Metal-rich brines may also be responsible– Carry iron from the deep ocean (near

hydrothermal vents)– Deposited in shallow seas where it has access to

free oxygen

Carbon Isotopes

• 12C and 13C are stable isotopes• More energy efficient to make 12C bonds• 12C is preferentially incorporated into

products of chemical reactions (like photosynthesis!)

• Ratio of the two isotopes can be used as an indicator of biological processes

Carbon Isotopes

• If 12C has preferentially been incorporated, 13C/12C will be smaller than the standard

• If sample < standard, δ13C is negative


€

δ13C =13C

12Csample

13C12Cs tan dard

−1 ⎡ ⎣ ⎢

⎤ ⎦ ⎥×1000

Extreme EnvironmentsExtreme Environments

ASTR/GEOL 3300September 18, 2009

ASTR/GEOL 3300September 18, 2009

OverviewOverview

• Extreme Conditions• Other Worlds

• Extreme Conditions• Other Worlds

Extreme conditionsExtreme conditions

• Conditions on early earth may have been “extreme” compared to present-day

• Extremophiles - organisms that thrive in exteme environments– Heat/Cold– Acids/alkalines– High pressures– dessication

• Conditions on early earth may have been “extreme” compared to present-day

• Extremophiles - organisms that thrive in exteme environments– Heat/Cold– Acids/alkalines– High pressures– dessication

TemperatureTemperature

• Majority of organisms on Earth thrive in the temperature range 20-45 °C (mesophiles)

• Usual response to extreme temperatures:– Cold:

• Formation of ice crystals in the body

– Hot: • Structural breakdown of biological molecules

(proteins and nucleic acids)• Disruption of cells’ structural integrity due to

increased membrane fluidity

• Majority of organisms on Earth thrive in the temperature range 20-45 °C (mesophiles)

• Usual response to extreme temperatures:– Cold:

• Formation of ice crystals in the body

– Hot: • Structural breakdown of biological molecules

(proteins and nucleic acids)• Disruption of cells’ structural integrity due to

increased membrane fluidity

Extreme Conditions

TemperatureTemperature

Extreme Conditions

ThermophilesThermophiles

Extreme Conditions

•Thermophiles live between 50 and 80 °C –Example: Thermoplasma

•Archaea•Lives in volcanic hot springs

•Hyperthermophiles live between 80 and 115 °C–Example: Sulfolobus

•No multicellular plants or animals can tolerate >50 °C•No microbial eukarya can tolerate >60 °C

ThermophilesThermophiles

• First true thermophile discovered in Yellowstone National Park in 1960s

• > 50 hyperthermophiles have been isolated to date– Many live in or near

deep-sea hydrothermal systems (black smokers)

• First true thermophile discovered in Yellowstone National Park in 1960s

• > 50 hyperthermophiles have been isolated to date– Many live in or near

deep-sea hydrothermal systems (black smokers)

Extreme Conditions

Thermophiles: how they cope

Thermophiles: how they cope

• Since high temperatures change membrane fluidity, adaptation is change of membrane composition

• Evolution of proteins to better cope w/ high temps

• Since high temperatures change membrane fluidity, adaptation is change of membrane composition

• Evolution of proteins to better cope w/ high temps

Extreme Conditions

PsychrophilesPsychrophiles

• Supported in frozen environments of Earth

• Lowest recorded temperature for active microbial communities: -18 °C

• Found in all 3 domains of life

• Supported in frozen environments of Earth

• Lowest recorded temperature for active microbial communities: -18 °C

• Found in all 3 domains of life

Extreme Conditions

Psychrophiles: how they cope

Psychrophiles: how they cope

• Low temps mean decrease in membrane fluidity, so adaptation is adjustment of ratios of lipids in their membranes

• Prevent water from freezing with soluble compounds that lower freezing temp of water (e.g. thermal hysteresis proteins)

• Low temps mean decrease in membrane fluidity, so adaptation is adjustment of ratios of lipids in their membranes

• Prevent water from freezing with soluble compounds that lower freezing temp of water (e.g. thermal hysteresis proteins)

Extreme Conditions

RadiationRadiation

• UV and ionizing radiation can do serious damage to DNA– Deinococcus

radiodurans can withstand high-dose radiation because it can accurately rebuild its DNA

– Also able to cope with extreme dessication, so also a xerophile - thus known as a polyextremophile

• UV and ionizing radiation can do serious damage to DNA– Deinococcus

radiodurans can withstand high-dose radiation because it can accurately rebuild its DNA

– Also able to cope with extreme dessication, so also a xerophile - thus known as a polyextremophile

Extreme Conditions

pHpH

• Most biological processes occur in middle of pH scale (4-8)

• Acidophile - thrive at 0.7-4• Alkaliphile - thrive at 8-12.5

• Most biological processes occur in middle of pH scale (4-8)

• Acidophile - thrive at 0.7-4• Alkaliphile - thrive at 8-12.5

Extreme Conditions

pHpH• Acidophile - thrive at 0.7-4

– Occur in geochemical activities

• Sulfur production at hot springs and deep-sea vents

– Cope by pumping H+ out of cells at a high rate

• Alkaliphile - thrive at 8-12.5– Live in soils containing

carbonate and soda lakes

– Above pH of 8, RNA breaks down, so alkaliphiles maintain neutrality inside cells

• Acidophile - thrive at 0.7-4– Occur in geochemical

activities• Sulfur production at hot

springs and deep-sea vents

– Cope by pumping H+ out of cells at a high rate

• Alkaliphile - thrive at 8-12.5– Live in soils containing

carbonate and soda lakes

– Above pH of 8, RNA breaks down, so alkaliphiles maintain neutrality inside cells

Extreme Conditions

Acidic mudpotAcidic mudpot: located in Yellowstone NP, home of Sulfolobus acidocaldarius. Photo courtesy of National Park Service

SalinitySalinity

• Halophiles require high concentrations of salt to live (2-5 times that in seawater)

• Found in Great Salt Lake, Dead Sea, salterns

• Can be coincident with high alkalinity environments

• Survive by producing large amounts of internal solute so as to not lose water via osmosis

• Halophiles require high concentrations of salt to live (2-5 times that in seawater)

• Found in Great Salt Lake, Dead Sea, salterns

• Can be coincident with high alkalinity environments

• Survive by producing large amounts of internal solute so as to not lose water via osmosis

Extreme Conditions

Great Salt Lake, UT.Great Salt Lake, UT. Carotenoids seen here are biproduct of halophiles.

DessicationDessication

• Some organisms survive low-water environments via anhydrobiosis, a state of suspended animation

• Some organisms survive low-water environments via anhydrobiosis, a state of suspended animation

Extreme Conditions

PressurePressure

• Undersea pressures are much greater than surface pressures– Boiling point increases with pressure, so

liquid water at ocean floor could be 400 ºC– Pressure compresses volume, so peizophiles

have increased membrane fluidity so they don’t get “smushed”

• Upper atmosphere pressures are much lower than surface pressures

• Undersea pressures are much greater than surface pressures– Boiling point increases with pressure, so

liquid water at ocean floor could be 400 ºC– Pressure compresses volume, so peizophiles

have increased membrane fluidity so they don’t get “smushed”

• Upper atmosphere pressures are much lower than surface pressures

Extreme Conditions

OxygenOxygen

• Aerobic metabolism is more efficient than anaerobic, but it kills cells quicker via oxidation

• Many organisms with aerobic metabolisms combat oxidation with natural anti-oxidants

• Aerobic metabolism is more efficient than anaerobic, but it kills cells quicker via oxidation

• Many organisms with aerobic metabolisms combat oxidation with natural anti-oxidants

Extreme Conditions

Extremes on other planetsExtremes on other planets

• If we’ve seen life thrive in extreme circumstances on Earth, why not on other planets?

• Mars holds most promise• What about moons in our solar system:

– Europa– Titan– Enceladus

• If we’ve seen life thrive in extreme circumstances on Earth, why not on other planets?

• Mars holds most promise• What about moons in our solar system:

– Europa– Titan– Enceladus

Other Worlds

Possible Earth analoguesPossible Earth analogues

• Hotsprings• The deep sea• Hypersaline environments• Evaporites• The atmosphere• Ice, permafrost, snow• Subsurface environments

• Hotsprings• The deep sea• Hypersaline environments• Evaporites• The atmosphere• Ice, permafrost, snow• Subsurface environments

Other Worlds

EuropaEuropa

• Life exists w/o photosynthesis in the deep ocean

• Europa has a subsurface ocean

• Life may exist beneath the surface



• Life may exist beneath the surface

Other Worlds

EuropaEuropa



• Life may exist beneath the surface– Shielded from

Jupiter’s radiation– Warmer than surface

temperatures



• Life may exist beneath the surface– Shielded from

Jupiter’s radiation– Warmer than surface

temperatures

Other Worlds

TitanTitan

• Airborne micro-organisms?• Extremes to withstand:

– Dessication– Radiation

• Airborne micro-organisms?• Extremes to withstand:

– Dessication– Radiation

Other Worlds

TitanTitan

• On Earth, spores are only things that really “live” in the atmosphere.

• Debate as to weather this constitutes life

• On Earth, spores are only things that really “live” in the atmosphere.

• Debate as to weather this constitutes life

Other Worlds

Mars

• Host to several extreme environments– Deserts– Ice, permafrost, snow– Subsurface

Other Worlds

Mars: deserts

• Driest places on earth– Hottest: Atacama – Coldest: Antarctica

• Bacteria, algae, fungi live on or under rocks– Endoliths– Cryptoendoliths

• Rocks provide shelter from – Temperature extremes – UV radiation

Other Worlds

Mars: ice, permafrost, snow

• Microbes and algae exist in frozen environments on Earth

• Maybe not thriving, but microbial survivors could exist

Other Worlds

Mars: subsurface environments

• Best chance of withstanding Martian extremes– No liquid water at surface

– Low pressure

– CO2-rich atmosphere

– Only 43% solar radiation at Earth

• Subsurface provides– Protection

– Possible liquid water

– Energy source for chemolithoautotrophs

Other Worlds

Documents

Habitability Bonnie Meinke January 27, 2009 Bonnie Meinke January 27, 2009