Life in “Extreme” Terrestrial

Environments

Promising Discoveries for the Potential of Extraterrestrial Life

Eric LaMotte12/5/2006

Introduction• Beliefs held a few decades ago:

– All life on Earth requires photosynthesis– All life on Earth shares a common metabolic

structure– Life does not exist in “extreme” environments

• Current beliefs:– Photosynthesis is not necessary for life– Life can utilize practically any redox pair that

yields and exothermic reaction– Life exists in places we never thought possible,

such as 4000m deep in the ocean.

• What we will believe in a few decades– ???

}Huge implications for Astrobiology

Where can extremophiles thrive?T above 110°C

T below 15°CLow water availability

High salinities

High pressuresLow sunlight

…as well as below pH 3, above pH 9, in areas with high heavy metal concentrations, and more…

What is an “Extreme Environment”?

Objective Criteria?

“There is a true ‘middle ground’ where life’s

information is stable but its processes are dynamic”

SubjectiveCriteria?

“We only call it extreme because it is unlike ours”

…OR…

What we consider to be objective criteria may someday be considered subjective criteria

Extremophiles – Adaptationsand Metabolism

Extremophiles have adaptations that make the sensitive macromolecules – nucleic acids, proteins – more stable under their conditions

Their domain, the archaea, are able to metabolize practically any available redox pair that yields energy when utilized.

Redox PairsCosmic Abundances

The Antarctic Cold Desert

• A dessicating environment sucks all moisture away from surface and atmosphere

• The environment is cold and wildly varying in Temperature

• This environment is considered to be closer to that of Mars of any environment on Earth

• Microbes live literally inside the rocks (which they metabolize), where there are small amounts of water, in order to survive

Life found a habitable microenvironment within an inhospitable macroenvironment

Hydrothermal VentsUp to 4km under the sea, arcobacteria oxidize H2S to

fuel life at hydrothermal vents

Their metabolism powers a whole ecosystem of clams, crabs, scallops, shrimp, and tubeworms (to name a few)

A black smoker

Black = Metal Sulfide

Clear = Anhydrite Crystals

Tubeworms

Crabs

Rosebud Site, WHOI

Rose Garden, WHOI

Calyfield Site, WHOI

Clams

Extreme Environments and Complex Life

• Intelligence requires complexity, which is characteristic of eukaryotes

• As shown in the hydrothermal vents, eukaryotic life CAN survive in extreme conditions

• However, they cannot survive in AS extreme conditions, and they lack the metabolic versatility of the archaea

The complex machinery of eukaryotic life is its weakness – there are more “parts” of the

machine that break more easily

Origins of Life

• Evidence shows that our earliest tracable ancestors were hyperthermophiles

• This does not mean that the first life on Earth was hyperthermophilic

• Still, if the first life wasn’t hyperthermophilic, then it must have evolved to become so very quickly.

Conclusion

• The vast discoveries of extremophilic life on Earth has profound implications on the possibilities of discovering life elsewhere

• The evidence also shows us that life might be more difficult to detect, since it has so many varied forms and hard-to-reach habitats