Tori M. Hoehler NASA Ames Research Center

1. Adaptation and Survival on Planetary Scales Tori M. Hoehler NASA Ames Research Center

3. The Drake Equation: N = R* fp ne fl fi fc L N = The number of communicative civilizations R* = The rate of formation of suitable stars fp = The fraction of those stars with planets. ne = The number of Earth-like worlds per planetary system fl = The fraction of Earth-like planets where life actually develops fi = The fraction of life sites where intelligence develops fc = The fraction of communicative planets (those on which electromagnetic communications technology develops) L = The "lifetime" of communicating civilizations

4. Challenges Adaptability Once the origin of life occurs, how resilient is a biosphere to changes that occur over a planet’s lifetime? Our single example suggests that life can be resilient on time scales of at least 1/3 the age of the solar system

5. Any of the factors we identified as “extremes” could constitute a challenge to the long-term stability of life Resource Limitation Harsh conditions for biomolecules (energy, materials, solvent) (temperature extremes, radiation, pH, unsuitable chemistry)

6. Stars Evolve – as they do, their temperature, light emission, and even size change

7. Planets Evolve . . . (for one thing, they start hot and cool off)

8. Too Cold Too Hot Just Right? The Importance of Heat Flow Heat flow → volcanism, crustal turn-over

9. Volcanoes Bring Mantle Chemistry to the Surface

10. A chemically differentiated planet is like a battery . . . = (but the battery is only tapped when volcanoes and vents operate)

11. Climate Fluctuates, Sometimes Dramatically

12. Saltier Ultimately No Light Colder More Radiation? More Acidic? Mars Through Time?

13. “Stuff” Happens

14. Hiroshima Terrestrial Impact Frequency year Tunguska century Tsunami danger ten thousand yr. Global catastrophe “Armageddon” Impact (Texas-sized!) million yr. K/T billion yr. 0.01 1 100 10,000 million 100 million TNT equivalent yield (MT) (Credit: D. Morrison) “Catastrophic” depends on who you are and where you live . . .

15. 0 Heat-Sterilized Impact Heating Depth (km) 1 Geothermal Gradient 2 0 100 200 Temperature (°C) Surface-Sterilizing Impacts Habitable (Sleep & Zahnle, 1998)

16. Resource Recycling Energy Budget Chemistry Climate Life Alters its own Environment

17. Energy Balance (Used solar radiation to “charge up” the Earth’s chemical battery (by creating very oxidizing conditions at the Earth’s surface) Oxygen Production (Toxic for some, great for others – shifted the “balance of power”) Climate (Consumed CO2 and may have altered the production of other greenhouse gases (e.g., from methanogens, who are sensitive to O2) – this must have affected greenhouse warming and climate) Radiation Budget (Produce ozone (from O2), which created a shield for UV – less radiation = clement conditions for a greater variety of organisms) The Case of the Cyanobacteria . . .

18. How can life survive (thrive!), in the face of all these potential challenges, on time scales comparable to the lifetime of a solar system?

19. At an individual level, versatility is important Metabolism Tolerance to Extremes *These factors may sometimes be at odds

20. At the level of the whole biosphere, diversity is key

22. Sufficient Rates of Evolution Diversity of Niches, Into Which Organisms Can Evolve (these have worked on Earth for 3+ billion years) Technological Innovation (?)

23. Questions?