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A strobiology

A strobiology. Announcements. Homework #4 due on Thursday Quiz #2 on Thursday Closed book, closed note, no electronic devices Chapters 9, 10, and 11 Lecture material up through this Thursday. What is astrobiology?. NASA Astrobiology Program seeks to answer: How does life begin and evolve?

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A strobiology

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  1. Astrobiology

  2. Announcements • Homework #4 due on Thursday • Quiz #2 on Thursday • Closed book, closed note, no electronic devices • Chapters 9, 10, and 11 • Lecture material up through this Thursday Astrobiology 3/20/12

  3. What is astrobiology? • NASA Astrobiology Program seeks to answer: • How does life begin and evolve? • Does live exist elsewhere in the universe? How can we detect it? • What is the future of life on Earth and Beyond? Astrobiology 3/20/12

  4. Properties of life Astrobiology 3/20/12

  5. Properties of life Order, organization (organs, tissues, cells, molecules, atoms) Energy utilization and production (metabolism) Maintenance of internal constancy (homeostasis) Reproduction, growth, and development Response to the environment (react to stimuli) Evolutionary adaptation (slow change) Astrobiology 3/20/12

  6. Is it alive? Astrobiology 3/20/12

  7. Is it alive? Astrobiology 3/20/12

  8. Is it alive? Astrobiology 3/20/12

  9. Is it alive? Astrobiology 3/20/12

  10. Is it alive? Astrobiology 3/20/12

  11. Is it alive? Which is alive? Astrobiology 3/20/12

  12. Definition of life • “A system capable of evolution by natural selection” (Carl Sagan, 1970) • “A self-sustaining chemical system capable of undergoing Darwinian evolution” (NASA’s definition) Astrobiology 3/20/12

  13. Necessities of life • To search for life we need to know the requirements for life • These are based on our only reference system: Earth • Life requires: • Organic molecules: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur (CHONPS) • A source of energy • The presence of a solvent: liquid water • Suitable environmental conditions (for example temperature and pressure) Astrobiology 3/20/12

  14. Origin of life - Primordial soup theory Basic building blocks of life combined to form complex organic molecules such as amino acids, proteins, and an early version of RNA in a warm pond or ocean. Astrobiology 3/20/12

  15. Synthesis of small organic molecules – Atmosphere Miller-Urey Experiment: (1952) A spark (analogous to lightning) breaks apart C4H, NH3, and H2O components of the ancient atmosphere and the atoms recombine to form simple organic molecules. Astrobiology 3/20/12

  16. Problems of organic synthesis via Miller-Urey experiment The composition of the ancient atmosphere is not well known  might have had less C4H and NH3 than assumed by Miller and Urey Organic production by spark discharge is not very efficient in a CO2 rich atmosphere However, if CH4/CO2 < 0.1 very few organics are produced Astrobiology 3/20/12

  17. Synthesis of small organic molecules –Hydrothermal Vents • Problems: • Only very simple organics are generated • Complex organics are unstable at high temperatures Hydrothermal vents are fissures in a planet’s surface which geothermally heat water Near hydrothermal vents, silicate rocks, CO2, and H2O combine to form simple organic molecules Astrobiology 3/20/12

  18. Synthesis of small organic molecules – Extraterrestrial Problems: • Simple organics only • It’s hard to accumulate enough organics in one place Murchison (1969, Australia) Meteorites sometimes contain amino acids and other organic molecules Astrobiology 3/20/12

  19. The Dilution Problem • Earth’s early oceans were probably too dilute in simple organic molecules to form bigger molecules • Possible concentration mechanisms • Tidal pools (evaporation) • Freezing water • Mineral catalysts – small organic molecules could have stuck to the mineral surface in an organic film. Astrobiology 3/20/12

  20. Origin of life summary Astrobiology 3/20/12

  21. Extremophiles • Organisms that thrive in extreme conditions such as high or low temperature, high pressure, salty water, acidic water, low amounts of water, and/or high radiation environments • The earliest living organisms on Earth were extremophiles. • The atmosphere had very little oxygen, so there was no protection from UV radiation • The oceans were hot and probably acidic because of volcanism Astrobiology 3/20/12

  22. Temperature High temperature – proteins denature, chemical reactions slow down Pyrolobusfumarii – lives in hydrothermal vents. The upper limit for active growth is 121°C (250°F), but it can survive up to 130°C (266°F). Astrobiology 3/20/12

  23. Temperature Grylloblatids – ice bugs – body fluids act as antifreeze Snow algae – cold-tolerant algae grows on snow and ice Low temperature – water freezes which breaks cell membranes Current lower limit for active growth is -20°C Astrobiology 3/20/12

  24. Pressure Halomonassalaria High pressure can make cell membranes relatively impermeable for nutrients Current upper limit is > 1000 atm (pressure at Earth’s surface is 1 atm) Astrobiology 3/20/12

  25. Salinity Dunaliellasalina– pink micro-algae found in sea salt fields Proteins are less soluble at high salt concentrations Astrobiology 3/20/12

  26. Acidity (pH) Tinto river (Andalusia Spain) – pH ≈ 2 contains aerobic bacteria • pH = -log[H+] The amount of H+ measures the acidity of a solution (pH = 0 is most acidic; pH = 14 is most basic) • Current limits: • pH ≈ 0 Ferroplasma acidarnamus(acid mine drainage, CA) • pH ≈ 13 Plectonema (soda lakes) Astrobiology 3/20/12

  27. Water availability • Tardigrades – “water bears” • ~1mm • Anydrobiosis - their body desiccates and waits for moisture to return • While in anydrobiosis they can survive • -272.95°C for 20 hours • -200°C for 20 months • +120°C (above boiling) • Pressures of 1,000 atm • Pure vacuum Extreme desiccation can cause irreversible phase changes to lipids, proteins, and nucleic acids Astrobiology 3/20/12

  28. Radiation • DeinococcusRadiodurans • Can survive cold, dehydration, vacuum, and acid • Can survive 1000 times radiation amounts that would kill humans • Carries between 3 and 10 copies of its DNA, so it can make repairs after damage from radiation or dehydration Radiation damages DNA Astrobiology 3/20/12

  29. Endoliths Bacillus infernus– lives up to 3 km beneath Earth’s surface. Photo courtesy of US Dept. Energy Anaerobic organisms that survive by eating Fe, K, or S (rock) and live between the mineral grains of a rock Astrobiology 3/20/12

  30. Looking for life in the solar system • These ‘extreme’ environments on Earth may be ‘normal’ in other parts of the solar system • Life requires: • Organic molecules: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur (CHONPS) • A source of energy • The presence of a solvent: liquid water • Suitable environmental conditions (for example temperature and pressure) • NASA’s approach is: Follow the water! Astrobiology 3/20/12

  31. Why water? H and O are abundant in the universe It remains liquid over a wide range of temperatures Usually substances sink when frozen, but water ice floats (underwater life can survive freezing temperatures at the surface) It’s a polar molecule, so it can dissolve some substances but not cell membranes Astrobiology 3/20/12

  32. Mars Mars has a similar composition to Earth, but its water is mostly frozen, it has a thin atmosphere, no ozone layer, no magnetic field, and is less geologically active. It may have been warmer and wetter in the past. Deep subsurface permafrost could harbor endolith (in rock) communities today. Astrobiology 3/20/12

  33. Mars • ALH8401, a Martian meteorite, has structures that were briefly considered to be fossilized remains of bacteria-like life forms • But all the evidence for life could be explained without life too. Astrobiology 3/20/12

  34. Europa The subsurface ocean could harbor life, especially if there are hydrothermal vents at the ocean floor. Astrobiology 3/20/12

  35. Europa Cracks in the ice shell open and close periodically due to tidal flexing. Photosynthetic life might be able to live in the cracks.

  36. Titan Image from the decent of the Huygens probe Solid ice surface, methane rain and lakes, thick atmosphere. Geology is similar to Earth except for composition. Organisms could be consuming hydrogen, acetylene, and ethane to produce methane (Cassini/Huygens data is consistent with but does not prove this). Astrobiology 3/20/12

  37. Venus? Enceladus? Venus has stable cloud layers 50 km above the surface with hospitable climates and chemical disequilibrium, so some speculate that microbes could live there. Enceladus spews water into space with discharge rates similar to Old Faithful geyser in Yellowstone National Park. Somewhere else? Astrobiology 3/20/12

  38. Outside our solar system – Extrasolar planets 762 extrasolar planets have been discovered as of yesterday, 3/19/12 (http://exoplanet.eu/catalog.php) More on detection of extrasolar planets and the types of planets that have been found in a few weeks… Astrobiology 3/20/12

  39. Habitable zone Minimum and maximum estimates for the extent of the habitable zone in our solar system. The region around a star where a planet can maintain liquid water on its surface Changes with time as the star evolves An atmosphere (greenhouse effect) or geologic activity could warm planet Salt can lower the freezing point of water Astrobiology 3/20/12

  40. How can we tell if a planet can support life? Look for oxygen Look for liquid water Analyze the reflected light from the planet to see if it has an atmosphere Look for signs of biological activity (methane) And rule out other explanations! Astrobiology 3/20/12

  41. The search for life on Earth • Simultaneous presence of O2 or O3 and a reduced gas (CH4 or N2O) is the best evidence for life • The Galileo mission observed Earth during a fly by • It detected oxygen and methane • We could detect life on Earth! • We are beginning to try to do this for extrasolar planets Astrobiology 3/20/12

  42. SETI Search for ExtraTerrestrial Intelligence Started in early 1960s (institute was founded in 1984) Looks for non-random electromagnetic signals transmitted by intelligent civilizations SETI@home: volunteer use of internet connected computers to analyzed radio-telescope data It has not found any other civilizations yet Astrobiology 3/20/12

  43. The Drake equation What is the probability that we are not alone? The Drake equation attempts to estimate the number of civilizations capable of interstellar communication: N = Rs× fp× np× fL× fi× fc× Lc Rs= rate of sun-like star formation (best known factor: 1-10) fp = fraction of stars with planets (0.2-0.5) np= number of habitable planets per star (0.1- 5) fL = fraction of habitable planets with life (0.0001-1) fi = fraction of planets where intelligent life evolves (0.001-1) fc= fraction of intelligent civilizations capable of interstellar communication (0.01-1) Lc = average lifetime of those civilizations (60 yrs – ???) Astrobiology 3/20/12

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