1. Extra-Terrestrial Life (Chapter 20) Unlinked DNA under an electron microscope Fidelity Systems

2. Student Learning Objective Asses the probability of intelligent life elsewhere in the universe.

3. What defines life?  The primary condition that distinguishes living from non-living is DNA.  Chemical recipe for life  Can be copied (information passed to next generation)  May mutate to adapt to an environment  Life on Earth requires carbon, and water.

4. What are the theories for the origin of life on Earth? Outer Space Hypothesis  Reproducing molecules arrived here from space. Primordial Soup Hypothesis  Earth’s early oceans had organic compounds (carbon compounds) that developed into complex organic compounds.

5. Timeline for Life Fossils indicate life began in ocean Oldest simple organisms 3.4 billion years ago Complex organisms appeared 540 million years ago Humanoid species appeared about 4 million years ago Microbes Image Credit: Popular Science

6. Questions to Consider 1) If the oldest organisms found indicate when life started on Earth, how many years after formation of the planet did the first life appear? 2) Does the appearance of humanoids occur relatively early or late in Earth’s history? What does this indicate regarding the types of stars which could have life supporting planets?

7. How are astronomers searching for extra-terrestrial life?  Astronomers listen for radio waves (SETI)  Earth has been sending radio transmission into space since 1906.

8. What is the probability of life?  The Drake equation is the probability equation. N c = (N * )(f P )(n HZ )(f L )(f I )(f S ) N*N* number of stars in our galaxy fPfP fraction of stars that may have planets n HZ number of planets that may be in the habitable zone fLfL fraction of HZ planets that may be suitable for life fIfI fraction of f L planets where intelligent life may evolve fSfS fraction of a star’s life available during which intelligent life may utilize communication

9. Question What is the current estimate for the number of intelligent communicative civilizations in our galaxy? http://www.space.com/25219-drake-equation.html