Astrobiology and The Origin of Life on Earth A Chemical Perspective

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Astrobiology and The Origin of Life on Earth- A
Chemical Perspective -

• Christopher Glein
• 2005 NASA Glenn Academy
• Mentor Al Hepp
• Photovoltaics and Space Environments Branch

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Introduction
Astrobiology - the study of the origins,
evolution, distribution, and future of life in
the universe.

• A multidisciplinary approach incorporating
  molecular biology, chemistry, ecology, planetary
  science, astronomy, information science, space
  exploration, and related disciplines.
• Asks three fundamental questions
• 1. How does life begin and evolve?
• 2. Does life exist elsewhere in the universe?
• 3. What is the future of life on Earth and
  beyond?

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Astrobiology is Not Science Fiction
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Goals of Astrobiology

• Understand the nature and distribution of
  habitable environments in the universe
• Explore for past and present habitable
  environments in the solar system
• Understand how life originates
• Understand how past life on Earth interacted with
  its environment

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Goals of Astrobiology

• Understand evolutionary and environmental limits
  of life
• Understand the principles that will shape the
  future of life, both on Earth and beyond
• Determine how to recognize biosignatures on other
  worlds

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Project Goals

• Investigate possible life environments in the
  solar system
• Apply thermodynamics to planetary and biological
  systems to determine life potential
• Search for the beginnings of metabolism
• Establish the connection between metal sulfides
  and the origin of life on Earth
• Perform experiments using simple model reactive
  sites
• Hypothesize on cold organometallic chemistry on
  Titan

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What is life?

• Definition
• A chemical system that
• undergoes Darwinian
• evolution and degrades
• high-quality energy from
• its environment in
• metabolism
• Common Assumptions
• Requires organic
• molecules and liquid water

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The First Living Entity

• The most popular hypothesis is that the first
  life form was a ribozyme a catalytic RNA
  molecule
• It can mimic with limited functionality both DNA
  and proteins

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The Origin of Life

• RNA molecules are complex molecules (contain
  1000s of atoms)
• Process Build from simpler precursor molecules
  that gradually self-assembled
• Question What molecules were present and how did
  synthesis occur?
• Consider two approaches
• - Thermodynamics
• - Experiments

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Thermodynamics

• The study of heat and energy and their
  relationship to material properties
• Define system of interest using state variables
  (pressure, temperature, composition)
• Quantitatively describe equilibrium directionality

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Systems
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The Solar System
Where is there life?
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Extreme Earth

• Terrestrial organisms can thrive in many extreme
  conditions
• - temperature (386 K),
• - pressure (1300 bar)
• - radiation (1000 J m-2)
• - desiccation
• - salinity (5 M NaCl)
• - pH (0-10.5)
• - oxygen fugacity
• - heavy metals
• - organic solvents

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Venus

• Hothouse world
• Greenhouse effect from dense CO2-rich atmosphere
• Surface temperature 735 K, Surface pressure
  92.1 bar
• Surface too hostile for life
• Clouds might have primitive life
• At 50 km, temperature 350 K, pressure 1 bar

• A disequilibrium atmosphere
• Sulfuric acid droplets with pH 0

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Mars

• Frigid, desert-like environment
• Tenuous atmosphere of CO2, N2, and trace gases
• Surface temperature 214 K, Surface pressure
  6.36 mbar
• Liquid water is not stable at the surface
• Large salt deposits found
• Possible hydrothermal life in subsurface water
  saturated with salts

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Europa

• A very cold place with no substantial atmosphere
• Surface temperature 103 K
• An icy crust 20 km thick covers a salty alkaline
  ocean (ionic strength 0.3, pH 10)
• Ocean depth 100 km (Mariana trench 11 km)
• Seafloor temperature 260 K, pressure 1.6 kbar
• Hydrothermal activity might support a viable
  biosphere

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Titan

• Icebox world
• Thick, mildly reducing atmosphere of N2, CH4, H2,
  and organics
• Surface temperature 94 K, Surface pressure 1.5
  bar
• Rivers and lakes of liquid methane
• Possible subsurface ocean of H2O-NH3
• Natural laboratory for assessing prebiotic
  chemistry

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Other Possible Abodes of Life
Enceladus
Triton
Mercury
Io
Ganymede
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A More Quantitative Look at Planetary scale
Thermodynamics

• Disequilibrium can be quantified using the Gibbs
  free energy
• Life creates disequilibrium by maintaining
  incompatible gases (i.e. CH4 and O2)
• Photosynthesis
• CO2 H2O ? CH2O O2
• Methanogenesis
• CO2 4H2 ? CH4 2H2O
• Combustion
• CH4 2O2 ? CO2 2H2O

?G ?G0 RT lnQ
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Entropy and Life
microbe open system of interest interior
irreversible chemical processes in cell Q heat
transfer matter matter transfer dS(microbe)
dS(from exterior exchange) dS(interior) dS(from
exterior exchange) dQ/T dS(matter) dS(microb
e) dQ/T dS(matter) dS(interior) dS(microbe)
0 (assume at steady state) -dS(interior)
dQ/T dS(matter)
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Entropy and Life

• 2nd Law The total entropy of the universe
  increases in spontaneous processes
• Exterior exchange helps cells stay in a state of
  low entropy at the expense of its surroundings.
• Life uses free energy from food to produce
  entropy and transfers it to the environment via
  heat (physical entropy) and metabolic byproducts
  (chemical entropy)

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Planetary Entropy
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Planetary Entropy

• Planets degrade low entropy solar energy to high
  entropy heat by physical and chemical processes
• Jupiters atmosphere is in a state of high
  chemical entropy and also has stable weather
  patterns
• Future Work Connect physical entropy, chemical
  entropy, and life.

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The Prebiotic World

• Iron-sulfur world hypothesis
• Life arose from reduced fluids reacting with
  metal sulfides
• Pyrite formation produces energy, ?G0 -38.4 kJ
  mol-1
• FeS H2S ? FeS2 H2
• Energy used for metabolism (make complex
  molecules)

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Protometablism

• Citric Acid Cycle is widespread in nature
• Metabolism came from an older, simpler version
• Sulfur intermediates were used
• Metal sulfides catalyze the reactions
• Lattice structure resembles modern enzymes
  (iron-sulfur clusters)

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Future Literature Work in Metabolism

• Search for prebiotic catalysts used in primitive
  bacteria and archea
• Find important catalyzed metabolic reactions.
  Include reactants, products, and metal active
  sites
• Search for target intermediates in metabolism

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Future Experimental Work in Metabolism

• Perform experiments at Cleveland State University
  
• Synthesize important metabolic intermediate
  compounds
• Determine relevant physical properties
• Write a concise report of my results and
  conclusions

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Organometallic Chemistry on Titan

• Collaborating with Chris McKay at NASA Ames
• A poorly investigated area of study
• Cold organic solvent system (liquid methane)
• Erosion and weathering observed
• Start with theoretical solubilities
• What kind of chemistry is going on???

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Acknowledgements

• Dr. Al Hepp
• Dr. Doug Ogrin
• Photovoltaics and Space Environments Branch
• 2005 NASA Glenn Academy
• Dr. M. David Kankam
• Office of University Programs
• Professor David Catling
• Dr. Chris McKay
• Washington NASA Space Grant
• Thank You!

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Questions