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Astrobiology

Stephan Hoyer Physics 120 Seminar 21 April 2008. Astrobiology. What does life look like?. Answers: Earth ???. Basic requirements for life. Solvent Liquid water Energy source Photosynthesis – 98% of energy Chemolithotrophic – chemical redox reactions

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Astrobiology

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  1. Stephan Hoyer Physics 120 Seminar 21 April 2008 Astrobiology

  2. What does life look like? Answers: • Earth • ???

  3. Basic requirements for life • Solvent • Liquid water • Energy source • Photosynthesis – 98% of energy • Chemolithotrophic – chemical redox reactions • Heterotrophic – other organisms • Elements necessary for life: • 98%: C,H, N, O, P, S • 2%: Na, Cl, K, F, Ca, Mg, B, Al, Si, Cr, Mg, Cu, Zn, Se, Sr, Mo, Ag, Sn, I, Pb, Ni, Br, Va

  4. Why water? • Some sort of liquid is necessary • Solid – no mixing • Gas – too light • Water is special • High heat capacity – stable temperatures • Expansion on freezing – keeps ice floating so it can eventually melt • High dielectric constant – keeps charged groups separate • Universal solvent – makes lots of reactions work

  5. Why carbon? • Structure is good for building complex molecules • Four bonds attaching to each C atom • Chirality • Far more common in the interstellar medium • 90 carbon containing molecules found • 9 silicon based molecules • The Earth is mostly silicon, but there’s carbon based life

  6. Animo acids in the lab Urey-Miller experiment: recreating primitive conditions of Earth Recently (2002): Bernstein et al create amino acids in conditions like interstellar medium at 15K

  7. Habilitability Too hot Just right (Mostly) too cold

  8. How does Earth stay habitable? • Run away positive feedback: • Snowball Earth • Greenhouse effect • Saved by negative feedback: • Carbonate-silicate cycle

  9. Carbonate-silicate cycle Hotter: faster weathering, more carbon gets trapped in the Earth Colder: slower weathering, more greenhouse gas Negative feedback Relies on volcanoes! From Kasting, J.F. and Catling, D. Annu. Rev. Astrophys., 41, 429-463 (2003)

  10. Habitability and temperature The “habitable” zone and the continuously habitable zone -> need to satisfy conditions for liquid water for sufficiently long time

  11. Limits of HZ: Europa Has a liquid water ocean under an ice crust Energy due to tidal forces from Jupiter Maybe there’s life down there?

  12. What sort of life should we look for? • Bacteria! • Only form of life for billions of years • Most abundent and diverse form of life • They use all sorts of energy sources • Extremophiles!

  13. Hot spring (Yellowstone)

  14. Grand Prismatic Spring (Yellowstone)

  15. Mud geyser (Iceland)

  16. Deep sea black smoker

  17. Extremophiles

  18. Survival vs. growth Surviving is way easier than growing

  19. Life from Mars? Bacteria like structures on meteorite fragment Source of life on Earth? 1996

  20. Acknowledgments These guys included powerpoints!

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