1. Micro fossil in a meteorite ? (R. Hoover 2011)

2. Lecture 7: Geologic History of Life Oldest signatures of life in sedimentary rocks: Microfossils Molecular fossils (mainly lipids) Stromatolites C and S isotopic signatures Pattern of nested similarity A fossil cyanobacterium in circa 1.5 Gyr old sedimentary rocks - (A. Knoll).

3. Microscopic fossils in ALH-84001 ?

4. Methane release on Mars - 2009

5. A hole on Mars ?

7. Lecture 9: Habitable zones 1.How do we define a habitable zone (HZ) ? 2.The habitable zone in the Solar System. 3.Life beyond the habitable zone ?

8. Defining a Habitable Zone: Range of distances from the star where the temperature on some of the surface of a rocky planet allows water to be liquid. (The planet must have enough mass to keep an atmosphere.)

10. Defining a Habitable Zone:

11. The phase diagram of pure water:

13. Three important properties of water: (1)Liquid in range of temperatures favorable to long-chain polymer forming; (2) Solid form (ice) floats in it own liquid - environmental stability; (3) Is a polar molecule - help membrane formation.

14. The Terrestrial Planets Mercury Venus Earth Mars

15. Mars - evidence for water

17. A changing Habitable Zone: The Sun, as all stars, evolves (burns its ‘fuel’ and changes structurally) - it will become cooler and larger. HZ: shaded - now, dashed - once.

18. A changing Habitable Zone:

20. Beyond the HZ: Radiant heating from a parent star is not the only way to provide an energy source: (1) Planetary interiors: radioactive & core heat Deep Biosphere Lab (Sweden): hyperthermophiles at depths of ~ 6 km (80 C). (2) Tidal heating

21. Beyond the HZ: Titan

22. Titan properties 50% silicates, 50% ices; probably differentiated Atmosphere is >90% N 2 and 2-5% CH 4 T s = 94K, P s = 1.5 bar : Titan :: : Earth Liquid CH 4 & Water ice Liquid H 2 O & Silicate rock Near triple point Similar mechanical strength

23. Lakes and channels on Titan!

24. Main points to take home: