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Life and Extremes

Discover the requirements, limitations, and diversity of life forms with insights into astrobiology's search for life beyond Earth. Learn about the importance of extremes and Earth's possible analogs for life in the universe. Key focus is placed on understanding habitability and defining life's boundaries.

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Life and Extremes

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  1. Life and Extremes Tori Hoehler NASA-Ames Research Center

  2. Astrobiology Seeks to Understand the Origins, Evolution, Distribution, and Destiny of Life in the Universe.

  3. Think Globally, Act Locally . . . In Astrobiology: Think as broadly as possible about our key questions (or risk missing something important) Be practical about where to look and what to look for (that’s the only way to design discerning missions)

  4. What is Life? Requirements and Limitations “Extremes”

  5. Capable of reproducing itself (Can carry out chemical reactions and synthesis) (Can harness energy from the environment to drive these chemical processes) Capable of Darwinian evolution (mutation and natural selection) So what is life, anyway? Some Commonly Cited Attributes:

  6. Does Something Keeps on Doing Something (Longer than if it were Not Alive) So what is life, anyway? Life According to Erwin Schrödinger (1944):

  7. Raw Materials Tools & Machinery A Blueprint Energy & Work The Factory Analogy for Life (cells are little factories that make more little factories) To build a new factory, we require:

  8. Blueprint, Machinery Doing anything with speed or specificity requires molecules that are very complex Big molecules required to store information

  9. Raw Materials (remember, we are talking about atomic materials) A basic building block that can be assembled into large, complex backbones Some interesting decorations to hang along the chain A way to connect the pieces together

  10. A lesson from Earth . . .

  11. Phosphorus & Nitrogen (backbone & decoration) Carbon (the backbone) Hydrogen (filler/ H-bonds) Sulfur, Oxygen (interesting decorations)

  12. These building blocks are connected together by chemical bonds Chemical bonds are made from electrons, of which life requires some source

  13. To do something, molecules need to interact This won’t happen (much) in the solid phase, because the molecules can’t come together across a significant distance. It could happen as a gas, but complex molecules are so big that they usually break down before they vaporize. So the molecules of life need to be dissolved in something. For Earth life, water is the solvent

  14. Energy Radiation (as visible light) Chemical Heat Mechanical

  15. Bottom Line Requirements for (our) Life Source of Energy Water Source of Carbon Nutrients Source of Electrons Microbiologists classify organisms based on how they fulfill these needs

  16. Life requires conditions that allow complex molecules to form and persist Possible Problems . . . Heat Radiation Strong Acid/Base Harsh Chemicals

  17. Any environment in which access to basic requirements is sketchy, or in which conditions threaten the stability of biomolecules, could be considered extreme Some extremes are absolute (universal to life), some are relative (specific to a particular kind of life) How can we define the limits for life?

  18. An Empirical Approach to Astrobiology Use the only life we know – life on Earth – as a guide to understanding the prospects for, and how to seek, life elsewhere in the universe.

  19. How valid is the Earth-analog approach? It’s the best we’ve got, so far . . . Demands a focus on common traits, avoidance of highly specific circumstances

  20. If we seek to broadly define life's capabilities and limits, microbes are the place to look

  21. Genetic Diversity

  22. Metabolic Diversity Macroscopic World Microbial World Aerobic (O2-based): Light Inorganic Chemicals Organic Matter Anaerobic: Light Inorganic Chemicals Organic Matter Plants Microbial Mat Animals

  23. Tolerance of Extremes . . . Hydrothermal Vent (T = 115 ºC) (Photo: NOAA) Halite-Saturated Ponds, SF Bay (Photo: NASA) Acid Drainage (pH -0.7), Iron Mountain, CA (Photo: C. Alpers & D. Nordstrom, USGS)

  24. High / Low pH Chemical Toxicity High / Low Temperature Desiccation / High Radiation (??) Some Yellowstone extremes

  25. Back to the Big Picture . . . Understanding extremes on Earth, especially with the broad example of microbes, helps us to define “habitability”. In a theoretical sense, this tells us how common life could be. In a practical sense, it tells us where and how to focus a search for life on other worlds.

  26. Questions?

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