Astrobiology and The Origin of Life on Earth

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 Glenn Research Center at Lewis Field

Introduction Astrobiology - the study of the origins, evolution, distribution, and future of life in the universe. 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? Glenn Research Center at Lewis Field 2

Astrobiology is Not Science Fiction But a new science combining multiple disciplines Glenn Research Center at Lewis Field 3

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 • Consider Astrobiology on Titan Glenn Research Center at Lewis Field 4

What is life? Definition A chemical system that undergoes Darwinian evolution and degrades high-quality energy from its environment in metabolism Common Assumptions Requires: • Free energy • Organic molecules • Liquid water (maybe!? ) Glenn Research Center at Lewis Field 5

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 Glenn Research Center at Lewis Field 6

The Origin of Life • RNA molecules are complex molecules (contain 1000’s 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 Glenn Research Center at Lewis Field 7

Thermodynamics → Glenn Research Center at Lewis Field → Systems → • 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 → 8

The Solar System Where is life? Glenn Research Center at Lewis Field 9

Extreme Earth • Terrestrial life thrives in many extreme conditions - temperature (235. 4 ˚F), - pressure (1300 bar) - radiation (1000 J m-2) - desiccation (= dry) - salinity (5 M Na. Cl) - p. H (0 -10. 5) - oxygen abundance - heavy metals (lead) - organic solvents (benzene) Glenn Research Center at Lewis Field 10

Venus • Hothouse world • Dense CO 2 atmosphere → Greenhouse effect • Surface temperature ~735 K, Surface pressure ~92. 1 bar • Active volcanism on surface • Clouds might have life • A disequilibrium atmosphere (bacteria? ) • Clouds → T ~350 K, P • But, acid cloud droplets, p. H ~0 ~1 bar Glenn Research Center at Lewis Field 11

Mars • Frigid, desert-like environment • Thin atmosphere: CO 2, N 2, trace gases • Surface temperature ~214 K, Surface pressure ~6. 36 mbar • Liquid water not stable at surface • Lots of big salt deposits • Maybe hydrothermal life below ground in salty water Glenn Research Center at Lewis Field 12

Europa • A very cold place (T~103 K) • Hardly has an atmosphere • Icy crust ~20 km thick covers a salty, basic ocean (ionic strength ~0. 3, SW~0. 7; p. H ~10, SW~8. 1) • Ocean depth ~100 km (Mariana trench ~11 km) • Seafloor T~260 K, P~1. 6 kbar • Hydrothermal vents could support life Glenn Research Center at Lewis Field 13

Titan • Icebox world • Thick, mildly reducing atmosphere; N 2, CH 4, H 2, organics • Surface temperature ~94 K, Surface pressure ~1. 5 bar • Rivers and lakes of liquid methane? • Subsurface ocean? • Good planetary lab for assessing prebiotic chemistry Glenn Research Center at Lewis Field 14

Other Possible Homes of Life Enceladus Io Glenn Research Center at Lewis Field Triton Ganymede Mercury 15

A More Quantitative Look at Planetary scale Thermodynamics Planetary Body Venus Chemical Potential Energy, ΔG (J mol-1) 1 Earth 11, 000 Mars 105 Jupiter 0. 4 Titan 2 • Disequilibrium given by Gibbs free energy • Life creates disequilibrium • Photosynthesis CO 2 + H 2 O CH 2 O + O 2 • Methanogenesis CO 2 + 4 H 2 CH 4 + 2 H 2 O • Combustion CH 4 + 2 O 2 CO 2 + 2 H 2 O ΔG = ΔG 0 + RT ln. Q Glenn Research Center at Lewis Field 16

Entropy and Life microbe – system of interest interior – irreversible reactions in cell Q – heat transfer matter – matter transfer d. S(microbe) = d. S(from exterior exchange) + d. S(interior) d. S(from exterior exchange) = d. Q/T + d. S(matter) d. S(microbe) = d. Q/T + d. S(matter) + d. S(interior) d. S(microbe) = 0 (assume at steady state) -d. S(interior) = d. Q/T + d. S(matter) Glenn Research Center at Lewis Field 17

Entropy and Life • 2 nd Law: The total entropy of the universe increases in all processes that happen • 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 gets rid of it via heat (physical entropy) and metabolic byproducts (chemical entropy) Glenn Research Center at Lewis Field 18

Planetary Entropy Glenn Research Center at Lewis Field 19

Planetary Entropy • Planets convert low entropy sunlight to high entropy heat • Jupiter’s atmosphere is in a state of high chemical entropy and also has stable weather patterns • What’s the connection between physical entropy, chemical entropy, and life? Nobody knows… Glenn Research Center at Lewis Field 20

The Prebiotic World • Iron-sulfur world hypothesis • Life arose from reduced fluids reacting with metal sulfides • Pyrite formation produces energy, ΔG 0 = -38. 4 k. J mol-1 Fe. S + H 2 S → Fe. S 2 + H 2 • Use this energy for metabolism (make complex molecules) Glenn Research Center at Lewis Field 21

Protometablism • Citric Acid Cycle is everywhere in nature • Modern metabolism came from an older, simpler version • Sulfur was used a lot • Metal sulfides catalyze the reactions • Mineral structure looks like enzymes (iron-sulfur clusters) Glenn Research Center at Lewis Field 22

Literature Work in Metabolism • Prebiotic catalysts used in primitive bacteria and archea: Iron, Nickel, Tungsten Complexes • Important metabolic reactions Sulfur metabolism, Methanogensis • Target intermediates in metabolism Acetate, Pyruvate Glenn Research Center at Lewis Field 23

Astrobiology on Titan • Current area of study with arrival of Cassini • Liquid methane is Titan’s version of water • Erosion and weathering (i. e. rain, rivers, lakes) • What kind of chemistry is going on down there? ? ? Glenn Research Center at Lewis Field 24

Atmosphere and Surface • Atmospheric reactions: CH 4 + N 2 → C-N organics • Surface is dynamic = cryovolcanism • Mix C-N organics with cryolava, what happens? • Study Titan to learn more about prebiotic chemistry and the origin of life Glenn Research Center at Lewis Field 25

Don’t Get Scared, but…. What if there’s life on Titan!? • Free energy C 2 H 2 + H 2 → 2 CH 4 Reaction gives 334 k. J/mol, Life needs ~42 k. J/mol • Organic molecules C-N organics falling from the sky • Solvent for life, uh, ? Glenn Research Center at Lewis Field 26

Liquid Methane as a Solvent of Life • Can a cold, nonpolar solvent work for life? • Low Temperatures and Concentrations → slow reactions • Slow reactions not good for life • Possibly fix it using enzymes - catalysis - molecular cookie cutting Glenn Research Center at Lewis Field 27

Origin of Life in Liquid Methane Glenn Research Center at Lewis Field 28

Origin of Life in Liquid Methane (cont. ) Sorry, but no animals on Titan Glenn Research Center at Lewis Field • Geothermal heat dies down • Water that life lives in slowly freezes • If organisms don’t migrate to liquid methane, they freeze to death • Strong evolutionary pressure to evolve adaptations • Might be biochemically impossible 29

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. Christopher Mc. Kay Washington NASA Space Grant Thank You! Glenn Research Center at Lewis Field 30

Questions Glenn Research Center at Lewis Field 31