1. Medium-Rare Earth

2. Rare Earth Right distance from star Right mass of star Stable planetary orbits Right planetary mass Jupiter-like neighbor Plate tectonics Ocean and continents Large moon Right tilt

3. Rare Earth Right number/size of giant impacts Right amount of carbon and iron Right atmospheric properties Right kind of galaxy Right position in galaxy Right orbit in galaxy Right history (Snowball Earth/ice age episodes)

4. Path toward complexity Is there only one evolutionary path to complex animals?

5. Radiative diffusion

6. Discussion Do you think evolution is a completely random process? Explain.

7. Example: Photosynthesis In order for photosynthesis to work, you need the right temperature blackbody curve and the right atmosphere.

9. Evolution Photosynthesis evolved on Earth to take advantage of the abundant energy supplied by the Sun. We only have one kind because that is the most efficient use of our Sun’s energy. The Sun didn’t just happen to have the perfect conditions to match photosynthesis

10. Convergent Evolution A number of different species evolve independently toward the same solution to optimize survival.

11. Does Earth have the perfect conditions and history for the formation and development of life, or did life though the process of evolution adapt to perfectly fit Earth’s conditions and history?

12. The Search for Extraterrestrial Intelligence

13. SETI Tesla – 1901 picked up signals “from Mars” on a large Tesla coil. Marconi – encouraged everyone to listen to Martian broadcast during the 1924 opposition with Mars.

15. Low energy radio waves Long wavelength radio waves get reflected from Earth’s ionosphere Early detections of extraterrestrial signals likely due to distant lightning strikes

17. Standard definition TV signal

18. Discussion Why are radio signals from natural sources not narrow, but very wide bandwidth?

20. Drake Equation N = R * × f planet × n e × f life × f intell × f civ × L

21. Discussion Do you think evolution, given enough time, will always produce intelligence? Explain.

22. Encephalization Quotient Plot of brain mass vs. body mass

26. Discussion Can you think of any reasons why evolution might favor animals with a lower EQ?

27. Discussion What do you think is meant by the expression “evolutionary arms race?”

28. Drake Equation N = 1/year × 1 × 1/10 × 1 × 1 × 1 × 100 years N = 10 civilizations in our galaxy that are currently able to communicate with us.

29. Distance between civilizations If N = 10, the average distance between communicating civilizations is about 9000 light years.

30. Signals from other civilizations 1.Radio/TV broadcasts 2.Interplanetary communications 3.Signal beacons

33. Interstellar de-coherence Charged particles in interstellar space tend to spread out or smear coherent radio signals. Interstellar radio messages may not be decipherable.

34. Discussion Are you in favor of the government funding SETI? Explain.

35. Current SETI searches 1.Targeted searches 2.Sky surveys 3.Serendipity

36. Allen Telescope Array 350 6-meter radio telescopes

41. WOW signal

42. Sagittarius

43. Discussion Despite repeated attempts a signal from this region of sky has never been detected again. Should we consider this evidence of extraterrestrial life?

44. Results After nearly 50 years of searching, no signals from alien civilizations have been detected.

45. Discussion SETI proponents argue that absence of proof is not proof of absence and we should continue SETI for thousands or millions of years if necessary. Do you agree, or is there a point at which we should give up?