Life in Alternate Environments

Life As We Know It

• the chauvinistic approach
• to survive, life requires the things humans need
  • oxygen (O₂), water, sunlight
• and requires the absence of things humans can't tolerate
  • ammonia, methane, UV radiation
• we define the BIOSPHERE as the envelope of land, air, and surface water on the Earth where "our kind" of life is found
• we define the CONTINUOUSLY HABITABLE ZONE (CHZ) as the region in space were a planet can support "our kind" of life
  • 0.95 - 1.5 AU around our sun
• we look for extraterrestrial life in places where we could live

The Origins of Life - Beginnings in a Harsh Environment

• from rock and fossil record, know the early Earth (>3.8 b.y. ago)
  • had little or no free O₂
  • no ozone screen to protect surface from UV radiation
• life began in this environment
  • using ammonia, methane, CO₂, water, UV radiation/lightning
  • need absence of either O₂ or water for life to start
  • eventually, life evolved and modified its environment
  
• first forms of life were anaerobes - microbes, bacteria, algae, etc.
  • don't need free O₂ for metabolic functions (O₂ is a poison)
  • by 3.0-3.8 b.y. ago, evolved photosynthesis - O₂-producing
  • start to poison their own environment
• evolved amphiaerobes - use O₂ when available (more efficient)
  • revert to anaerobic processes when O₂ not available
  • kept O₂ levels low for a time
• by 2.0 b.y. ago, had enough O₂ available in oceans and atmosphere for aerobes (strict O₂ users) to evolve - the Earth had been altered!

The Earth Continues to Amaze Us - Contemporary Harsh Environments

The Ocean Floor

• studies using submersibles and robots
• conditions at volcanic vents are "hostile"
  • high pressures (> 2km below sea level)
  • high temperatures - black smokers >150^oC
  • harmful chemicals - sulfur, CO₂
  • total darkness - sunlight doesn't penetrate to this depth
• found lush ecosystems around these types of vents
  • use heat and chemicals from vents
  • microbes that like extreme heat, eat hydrogen sulfide, start a food chain
  • tubal worms 8-10 feet long
• speculated as origins of life - hot and constant
• shows that "sterile" areas can actually be active

Extremophiles

• organisms that survive and thrive in extreme environments
• potential industrial usefulness - organisms have "survival kits" for coping
  • given us artificial sweeteners, "stonewash" jeans, genetic identification
• Thermophiles
  • like heat, >45^oC up to 150^oC
  • after 150^oC DNA chemical bonds start to dissolve
  • some microbes can live in boiling water
  • found in/near smokers, hydrothermal vents, hot springs
• Psychrophiles
  • cold lovers
  • found in arctic sea ice
• Acidophiles
  • like high acidity, pH<5       (water pH=7)
  • the acidity is strong enough to destroy DNA
  • organisms keep acid out of cell structure
  • found in hydrothermal vents, mine tailing and tailing ponds
• Alkaliphiles
  • like high alkalinity, pH>9       (water pH=7)
  • RNA breaks down at pH>8
  • organisms keep alkali out of cell structure
  • found in soda lakes (in African Rift Valley), carbonate soils
• Halophiles
  • love extremely salty water
  • in salt lakes, salt evaporation ponds

A Few Extreme Examples

• worms living on methane ice mounds in the Gulf of Mexico
  • mound of water and natural gas (methane is main component)
  • these freezes beneath the sediments and seep up as a solid
  • temp is 5^oC
  • water depth is 550 meters
  • pink, flat, centipede-like creatures 1-2 feet long, living in dense colonies
  • feed on bacteria, which feed on methane
• bacteria in the ground, living in pore spaces between rock particles
  • 1000's of meters below ground - at high pressure
  • reduce sulfates for energy
  • have a very slow metabolism - to endure starvation
  • cell division occurs on average once per century
  • can remain viable for geologically significant lengths of time

Possibilities of Life on Other Planets

Mars

• the Viking lander found no evidence for life
  • mass spectrometer found too little carbon
  • environment is highly oxidizing
• in past had wetter climate
  • early ocean due to warmer climate, denser atmosphere
  • was life possible then?
  • can we find fossils, or pockets where life survived?
  
• group of NASA scientists (Dave McKay and others) found possible fossils in a Martian meteorite
  • ALH84001 (Allan Hills) meteorite
  • meteorite from old Martian crust - 4.5 b.y. old
  • propose it contains biogenic minerals and microfossils
  • bacterially produced magnetite grains?
  • microfossils are much smaller than normally seen on Earth
• is this the origin of life on Earth?

Europa

• has the chemical requirements for life
• has a young icy surface
  • kept molten by tidal flexing
  • Galileo data shows linear features, rafts of broken ice?
  • look similar to fractures in sea ice in arctic areas of Earth
  • is the crust thin - 1km?
  • does it overly a liquid water or slushy asthenosphere?
• water asthenosphere may harbour primitive, microbial life
  • get energy from volcanic vents at bottom of asthenosphere
  • like ocean-floor vents on Earth but much deeper (60 km or more)
  • expect volcanic vents at least in early history of Europa

Enceladus

• most geologically active satellite of Saturn
  • kept active by tidal stresses
  • surface is relatively young
  • evidence for tectonic activity
• possibility for slushy asthenosphere at some time in body's history

Titan

• has nitrogen and methane atmosphere - similar to Earth except for O₂
  • can form organic molecules
• surface T is so low that probably have no liquid water
• impacts could melt ice locally - ice pools lasting up to 1000 yrs. may allow life-like chemical reactions to occur

Io

• is hot, and very geologically active
• has plenty of sulfur to sustain sulfur-consuming organisms

Jovian (gassy) planets

• speculation of massive gas-bag organisms (like jellyfish) in atmospheres of gas giant planets
• no corroboration for such speculation

Are We Star Stuff? - Extraterrestrial Origins for Life on Earth

• Mars - did life evolve on a warm wet Mars and "infect" Earth using Martian meteorites as the invasion fleet?
• Comets - contain all the chemicals required to manufacture organic molecules
  • did they bring the chemicals required to start life on Earth?
  • did they bring organic molecules which evolved into life on Earth?
  • do they bring viruses to Earth?
• Meteorites - some have been found to contain amino acids
  • did the building blocks of life in Earth evolve elsewhere?
  • were these responsible for the evolution of life on Earth?
  • could these have caused life to evolve on other planets?
  • Note: these amino acids aren't found in any living organisms

If you are interested in this topic...
Plan to attend the talk by

Jill Tartar
Mon. March 9, 1998
at the OISE building
Topic: Search for Extraterrestrial Intelligence (SETI) br>Previous: Lecture Eighteen

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